c© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim10.1002/14356007.a03 421

Beer 1

Beer

Hans Michael Esslinger, Freiberger Brauhaus Aktiengesellschaft, Freiberg/Sachsen, Federal Republic ofGermany

Ludwig Narziss, Freising, Federal Republic of Germany

1. Introduction . . . . . . . . . . . . . . . 12. Raw Materials . . . . . . . . . . . . . . 32.1. Starch-Containing Raw Materials . 32.1.1. Malting Barley . . . . . . . . . . . . . . 32.1.2. Malting Wheat . . . . . . . . . . . . . . 42.1.3. Unmalted Grains . . . . . . . . . . . . . 42.1.4. Other Sources of Extract . . . . . . . . 52.2. Hops and Hop Products . . . . . . . . 62.2.1. Resins . . . . . . . . . . . . . . . . . . . . 62.2.2. Hop Oil . . . . . . . . . . . . . . . . . . . 72.2.3. Polyphenols . . . . . . . . . . . . . . . . 72.2.4. Processing of Hops and Hop Products 72.3. Brewing Water . . . . . . . . . . . . . . 92.3.1. Salts . . . . . . . . . . . . . . . . . . . . . 92.3.2. Brewing Water Treatment . . . . . . . 102.4. Beer Yeasts . . . . . . . . . . . . . . . . 122.5. Auxiliary Materials and Brewing

Aids . . . . . . . . . . . . . . . . . . . . . 123. Production Technology . . . . . . . . 143.1. Malting . . . . . . . . . . . . . . . . . . . 143.1.1. Steeping . . . . . . . . . . . . . . . . . . 153.1.2. Germination . . . . . . . . . . . . . . . . 163.1.3. Kilning . . . . . . . . . . . . . . . . . . . 183.2. Technology of Wort Production . . . 203.2.1. Grinding of the Malt . . . . . . . . . . . 213.2.2. Mashing . . . . . . . . . . . . . . . . . . 223.2.3. Separation of Wort . . . . . . . . . . . . 233.2.4. Wort Boiling and Hopping . . . . . . . 243.2.5. Wort Treatment . . . . . . . . . . . . . . 263.3. Bottom Fermentation . . . . . . . . . 27

3.3.1. Fermentation . . . . . . . . . . . . . . . 283.3.2. Maturation . . . . . . . . . . . . . . . . . 293.3.3. Cold Storage . . . . . . . . . . . . . . . . 313.3.4. Filtration . . . . . . . . . . . . . . . . . . 313.3.5. Stabilization . . . . . . . . . . . . . . . . 313.3.6. Types of Bottom-Fermented Beers . . 323.4. Top Fermentation . . . . . . . . . . . . 323.5. Special Production Methods . . . . . 343.5.1. Dietetic Beer . . . . . . . . . . . . . . . . 343.5.2. Nutrient Beer . . . . . . . . . . . . . . . 343.5.3. Low-Alcohol Beer and Alcohol-Free

Beer . . . . . . . . . . . . . . . . . . . . . 343.5.4. High-Gravity Brewing . . . . . . . . . . 343.6. Filling . . . . . . . . . . . . . . . . . . . . 353.7. Beer Dispensing . . . . . . . . . . . . . 364. Properties and Quality . . . . . . . . 365. Analysis . . . . . . . . . . . . . . . . . . 375.1. Analysis of Raw Materials . . . . . . 375.1.1. Water . . . . . . . . . . . . . . . . . . . . 375.1.2. Malt . . . . . . . . . . . . . . . . . . . . . 375.1.3. Hops and Hop Products . . . . . . . . . 375.2. Brewhouse Control . . . . . . . . . . . 375.3. Wort . . . . . . . . . . . . . . . . . . . . 375.4. Fermentation . . . . . . . . . . . . . . . 385.5. Microbiological Process Monitoring 385.6. Beer . . . . . . . . . . . . . . . . . . . . . 385.7. Legally Required Controls . . . . . . 396. Economic Importance . . . . . . . . . 407. Physiology and Toxicology . . . . . . 418. References . . . . . . . . . . . . . . . . . 42

1. Introduction

Beer is described as a beverage containing al-cohol, extract, and carbon dioxide. Beer is pre-pared from barley malt, raw hops or other hopproducts, brewing water, and top- or bottom-fermenting yeast. The alcohol must be producedexclusively from these ingredients, which areconverted to fermentable products during thebrewing process. Barley malt may be combinedwith wheat malt, unmalted cereal adjuncts (rawgrain), and other extract-containing materials.Legal regulations concerning raw materials and

additives as well as rules for listing these varyfrom one country to another.

To obtain barley malt, the grain is germi-nated under controlled conditions; the controlscomprisemoisture content, germination temper-ature, the ratio of oxygen to carbon dioxide in thegerminating grain, and germinating time.Greenmalt is formed once a certain increase in en-zyme activity and a partial degradation of thestarchy endosperm have taken place; this lat-ter process is called by the brewer modification.Green malt is then processed into kiln or brew-

2 Beer

ing malt by drying. This malt is subsequentlymilled (ground) and mixed with brewing water.During the subsequent procedure, called mash-ing, highmolecularmass components ofmalt aredegraded by enzymes at specific well-definedtemperatures (rest periods). The suspension isfiltered to separate the liquid, called wort, fromthe spent grains. This process is called lautering.The wort is subsequently boiled with the addi-tion of hops; this causes a coagulation of con-stituents, which are then called hot trub or break.They are separated together with the solids fromthe hops (hot trub removal). The clarified wortis subsequently cooled to the pitching temper-ature required by the fermentation method andthe yeast strain used. The fermentation processis initiated by pitching: this consists of saturatingthe cold wort with air and adding cultured yeast.The fermentable low molecular mass compo-nents of the wort are converted to ethanol andnumerous aroma compounds (fermentation by-products) according to the metabolism of theyeast strain. After maturing to taste and enrich-ing with carbon dioxide produced by fermenta-tion, the beer is filtered to clearness and bottled.

The extract of original wort (original extract;original gravity) is defined as the mass fractionof nonvolatile, dissolved extract substances inthe unfermented, cold pitching wort. During fer-mentation most of these substances are metabo-lized by the yeast, and the content of extract con-tinually decreases. The extract of original wortcan, however, be determined in samples takenduring fermentation and in thefinished beer, pro-vided that the alcohol concentration and the realextract (extract contained in the dealcoholizedbeer) are both known.

The degree of attenuation is defined as theratio of fermented extract to original extract, ex-pressed as a percentage. The attenuation limitindicates the maximum amount of extract thatthe yeast will ferment.

Furthermore a distinction has to be made bet-ween top- and bottom-fermenting types of beer.The top-fermenting yeast rises to the surfaceat the end of the main fermentation process,whereas the bottom-fermenting yeast settles atthe bottom. Both yeast types differ morphologi-cally, in their enzyme composition, and in theirphysiological behavior.

The nomenclature of beer types is determinedby their general production method (see Chap.

3). Typical beer designations have developedfrom the natural chemical composition of thewater in various regions, e.g., Pilsener, Munich,Dortmunder.

In the Federal Republic of Germany, teach-ing and research in the area of brewing is con-centrated at the technical universities of Berlinand of Munich-Weihenstephan. The universi-ties of other European countries and of Japanalso have formidable research capacities. Fur-thermore, in numerous countries there are re-search facilities operated jointly with the brew-ing industry. In addition, there are the labora-tories of the large brewing companies, whichhave contributed greatly to the level of knowl-edge currently available. Results of research arediscussed at scientific meetings in Europe (Eu-ropean Brewery Convention, EBC) and at in-ternational meetings in the United States, SouthAmerica, Australia, and Japan.

History. Theword beer comes from theLatinword “bibere” (to drink), which is the originof the Old English word “beor” (the brewed),akin to the Old High German word “bior”, fromwhich also the French word “biere”, the Italian”birra”, the East European ”pivo”, and the Span-ish “cerveza” developed.

The roots of beer production, however, goback much farther to the first agrarian soci-eties, the Sumerers. They used a variety of graincalled emmer (Triticum dicoccum) which wasdehusked and baked to give flat bread. Theflat breads were soaked in water and then al-lowed to ferment spontaneously through the ac-tion of wild yeasts. The Babylonians developedthe art of brewing further and distinguished bet-ween twenty different types of beer, in whichthe emmer and barley content as well as thestrength of the beer were closely regulated. The“Codex Hammurabi” contained regulations re-garding the quality of beer and described strictpunishment for beer adulterators.

The Egyptians refined further the art of beerbrewing and the legal requirements. They madethe grain germinate and eliminated the soakedpieces of bread by sieving.

The Jews, Greeks, Romans, and Germanicpeoples all knew beer, but partly preferred wineas a drink. From the seventh century,malting andbrewing processes were researched with greatexperimental zeal, mainly in German monas-

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teries. In the following centuries, brewing anddipensing rights were loaned out to severalmonasteries. Itwas also themonkswhofirst usedhops as a flavoring agent. From the fourteenthcentury, hops were generally accepted as an ad-ditive; earlier, tree bark, bitter herbs, and berrieswere added to the brew.

Until the sixteenth century, only the sponta-neous top fermentation, which occurs at highertemperature, was known; later, bottom fermen-tation also was discovered.

War changed drinking habits because of thedestruction of cultural values. Bavaria, for in-stance, became a beer country only after theThirty Years’ War, when its vineyards were de-stroyed.

Beer as it is known today was only madepossible through numerous inventions in tech-nology. Hot air kilns, steam engines, refrigerat-ing machines, and filtration equipment enabledbrewers to work throughout the year. Increas-ingly, more precise control of the brewing pro-cess also became available. The most signifi-cant improvement in quality was finally accom-plished after the invention of the microscope:yeasts were found to cause the alcoholic fer-mentation. At the end of the nineteenth century,yeasts were cultivated and introduced into thebrewery as pure strains.

Purity Law. Laws that regulate the produc-tion of beer have always been regarded as con-sumer protecting regulations. One of these statu-tory regulations was laid down by the BavariandukesWilhelm IVandLudwigXat theStatePar-liament at Ingolstadt on April 23, 1516; the lawwas accepted and is known today as the PurityLaw (Reinheitsgebot). It requires that only bar-ley (barley malt), hops, and water are to be usedfor the production of beer; yeast, as the fourthraw material, was only mentioned for the firsttime in1551. Germany,Greece, andSwitzerlandbrew according to this very strict law, the oldestin the world that pertains to food processing.

Other sources of extract and numerous addi-tives and brewing aids are permitted in countrieselsewhere. Because brewing technology doesnot require additives and chemicals for the pro-duction of beer of a consistently high quality, thePurity Law brewers insist on the maintenance ofthe Purity Law.

2. Raw Materials

2.1. Starch-Containing Raw Materials

For further information, see also the articles on→ Cereals and Cereals Products, and on →Starch.

2.1.1. Malting Barley

Barley belongs to the family of grasses(Gramineae) and is found in various forms.First, a distinction is made between summerbarley (spring sowing) and winter barley (latefall sowing), and second, between two-row andmultiple-row barleys, according to the numberof blossoms on the stalk. Multiple-row barleysproduce malts richer in husks, protein, and en-zymes,whichmay prove advantageouswhen us-ing unmalted grain adjuncts. Two-row barley isdivided into two main groups: the straight bar-ley, and the “nodding” barley, whose ear hangsdown during maturation. Two-row spring bar-ley (Hordeum distichum nutans) has the bestmalting and brewing properties; the most im-portant varieties of spring barley in Europe areBarke (Germany, Denmark), Chariot (UK), Op-tic (France,Denmark,UK), Pasadena (Germany,Denmark), Reggae (Netherlands), and Scar-lett (France, Germany, Denmark, Netherlands).Two-row winter barley varieties are Plaisant(France), Pipkin (UK), Tiffany (Germany), andVanessa (Germany). The advantages of barleyover other grains that could be used for malt-ing are the easier regulation and control of thegermination process, the superior taste of beermade with barley, and the brewing technologyavailable. Barley grows best in a humid climateand on soils with moderate contents of nutri-tients. The husks produce a filter bed for lau-tering, and the enzyme complement is advan-tageous for bringing about the desired modifi-cation. A similar uniform development of ker-nels as in the two-row spring barley can only beachieved in the newly-bred two-row winter bar-ley varieties. Mixtures of spring and winter bar-leys cause technological difficulties in the malt-ing process. Because the developmental rhythmsof the two types of barley are different, the ger-mination process occurs unevenly when pro-cessing mixed charges. These problems may be

4 Beer

overcome by using separate malting processes,but processing difficulties can be expected in thebrewery in connection with lautering, fermenta-tion, and the filterability of the beer; an impairedbeer stability can also be expected.

Quality Requirements. Minimum specifi-cations are laid down in the EC quality standard.Moreover, themaltster puts further requirementson his raw material:

Germinative ability > 98 %Screening: > 90 % > 2.5mm (Vollgerste)Raw protein content < 11.5 %Extract > 80 %Attenuation limit > 80 %

Smell, color, gloss, and husk fineness arechecked by manual appraisement. Further me-chanical, chemical, andphysiological inspectionmethods are listed in [29], [30].

The most important malting attribute of bar-ley lies in its germinative vitality, which is de-fined as the percentage of kernels that initi-ate germination in the very beginning of themalting process. Freshly harvested barley mustpass through a post-maturation period. This dor-mancymaybe shortenedbyphysical or chemicalmethods.

The germinative energy is a measure of ger-mination maturity: it indicates how many grainshave actually germinated after three days underconditions that are similar to those used in prac-tice. A further indicator of maltability is the sen-sitivity of the barley to an overexposure to waterduring steeping (water sensitivity); the impor-tance of this criterion has declined following theapplication of extended air rest periods duringsteeping.

The standardization of pilot-scale maltingmethods has become an indispensable aid for theassessment of barley and optimization of malt-ing technology parameters; furthermore thesemethods provide reliable criteria in the selectionof newly-bred barley varieties for planting.

Directions for the cultivation, storage, andphysiological preservation of brewing barley, aswell as detailed descriptions of its morphologyand breeding, may be found in the literature [8],[10], [12], [13].

Chemical Composition. The chemicalcomposition of brewing barley versus a pale

malt is shown in Table 1. The moisture content,which is especially relevant to the storage qual-ity of freshly harvested barley, may range from12 to 20 %; 10 to 12 % are optimal for storage.As shown in Table 2, the moisture content isthe limiting factor for storage. The α-glucans(amylose and amylopectin of the starch) are themost important carbohydrates in barley. Othercarbohydrate components include β-glucans(cellulose, hemicellulose, gums), pentosans, aswell as minute portions of low molecular masssugars. Proteins are especially important formaltability, yeast nutrition, foam, taste, and thestability of the beer. Lipids are only partiallyused up during malting, the remainder stayingmainly in the spent grains. Other important com-ponents are phosphates (about 0.3 %), minerals(2.5 – 3.5 %), vitamins (about 0.5× 10−3%),and phenolic substances (about 0.2 %). The en-zymes of barley and of malt, as well as theireffects during mashing, are shown in Table 4.

2.1.2. Malting Wheat

For some top-fermenting beers (see Section 3.4)wheat malt is added in order to achieve a spe-cial flavor quality.Brewingwheat should contain11.5 – 12.5 % protein. Its extract yield is in therange of 83 to 87 %.

2.1.3. Unmalted Grains

Economic reasons or insufficient supplies ofbrewing barley or brewing malt have resultedin obtaining part of the starch by the additionof other, unmalted grain types. These adjunctsmayaccount for up to 30%of the grist inEurope,and up to 50 % in the United States. However,the success of this practice requires the use ofvery high enzyme-containing and protein-richbarley malts. In many countries these adjunctsare defined as replacement material for brew-ing malt, which add mostly carbohydrates to thewort; their use must be legally permitted.Unmalted barley does not present any eco-

nomic advantage over barley malt. Lower yieldsare achieved and frequently insufficient conver-sion in the brewhouse has to be corrected byadding enzymes produced microbially. Beersproduced in this manner contain less nitrogen,

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Table 1. The chemical composition of brewing barley and malt (mass fractions in %)

Malting barley Malt

As is Dry matter As is Dry matter

Moisture 12 – 14 4 – 5Starch 55 – 57 64 – 66 56 – 58 58 – 60Other non-nitrogen extractcompounds

12 – 14 14 – 16 16 – 18 17 – 19

Protein 9 – 10.5 10 – 12 8.5 – 10 9 – 11Fiber 4 4.5 5 5.2Minerals 2.5 2.8 2.4 2.5Fat 2 2.3 2 2.1

Table 2.Maximum storage time for maintaining malting barley quality under different storage conditions

Storage temperature Seed moisture content

10 % 12 % 14 % 16 %

8 ◦C 7.5 years 2.5 years 1 year 170 days10 ◦C 6 years 2 years 300 days 140 days12 ◦C 5 years 1.6 years 240 days 110 days14 ◦C 3.8 years 1.3 years 190 days 85 days16 ◦C 3 years 1 year 150 days 65 days

have a lower attenuation limit, and display bet-ter head retention, but filtration is more difficult.Unmalted wheat. Partially unmaltedwheat is

sometimes added to the mash. Its composition issimilar to that of barley.With a moisture contentof 15 %, wheat contains 65 % starch and othercarbohydrates, 12 – 14 % protein, and 1.7 % fat.Rice is processed as broken rice. This by-

product of table rice production must be purewhite. The moisture content is 12 – 13 %; otherconcentrations (expressedon adrybasis) are: ex-tract 93 – 95 %, fat 0.5 – 0.7 %, protein 8 – 9 %.Rice starch gelatinizes at 65 – 70 ◦C, sometimesonly at about 80 ◦C. The co-processing of ricegenerally results in very light and dry beers.Corn (maize) is processed as corn starch,

flakes, or larger corn grits, and is popular be-cause extract yields range from 87 to 91 % af-ter the removal of the oil-rich embryo. Moisturecontent should not exceed 12 – 13 %; proteincontent (dry basis) is in the range of 8.5 – 9 %; aresidual fat content of less than 1% in the grits isnot harmful to head retention. Addition of cornresults in sweetish, full-bodied beers. Commer-cial corn starch is practically free from proteinand fat. The final yield is about 103 %, becauseof the addition of water during enzymatic hy-drolysisSorghum, as a malt additive, has only re-

gional importance in Africa.

2.1.4. Other Sources of Extract

Other sources of extract are processed starchpreparations and carbohydrates in fermentablelowmolecularmass form.Besides starchflour it-self, syrups frequently are used,which aremanu-factured from grain or starch flour by enzymaticor acidic hydrolysis. All syrups have an extractcontent of about 80 %, while their fermentabil-ity is in the range of 40 – 78 %. They are addedto the wort kettle. The concentration of the wortmay be increased in this manner to 15 – 18 %without affecting the further process develop-ment adversely (see Section 3.5.4).Sugar is added to the wort kettle shortly be-

fore the end of boiling in order to raise the pro-portion of fermentable extract. Amounts up to15 % yield very soft beers with a wine-like fla-vor. For malt beers and nutrient beers, sugar isadded to the filtered beer in order to achieve thedesired character and extract of original wort.Sugar is added as sucrose, as invert sugar, or asglucose. For nutrient beers caramelized brewingsugar may be added. The extract content of thesugar solution is between 65 and 85 %, depend-ing on consistency and quality.

6 Beer

2.2. Hops and Hop Products

Hops added to the wort are an indispensable in-gredient formany reasons [7], [9]. They impart abitter taste to the beer, a specific aroma, and pro-mote clarification. Furthermore, they are con-sidered to have foam-improving qualities. Hopsalso are believed to act as an antiseptic in beer.The hop plant,Humulus lupulus, is a hardy, dioe-cious, climbing plant, and belongs to the hempfamily. Only female vines are planted in hopfarms; propagation is carried out by perpetuat-ing vegetative clones. Hop cultivation requiresspecial climatic conditions and a soil varyingin texture from sandy to muddy. The hop conesare of primary interest to the brewer. They rep-resent clusters of blossoms on the female plantandgrowdespite an absence of pollination.Hopsare picked in August or September. Yellowish-green, sticky, cup-like glands (lupulin glands)are located on the inner sides of the inner andouter bracteoles; they contain the aromatic andbitter substances.

Hops are classified according to their originand type; for similar varieties, the influence oforigin dominates. The cultivated types have beenobtained by separation according to shape. Clas-sification by type in the EC is made on the basisof the content of compounds responsible for thebitter taste and flavor:

1) EC List A aroma hops: Hallertauer, Hers-brucker, Perle, Saazer, Spalter, Tettnanger

2) EC List B bitter hops: Brewers Gold, Mag-num, Northern Brewer, Nugget, Target, Tau-rus

According to the certification policy withinthe EC hop market law, since 1978 produc-ers of hops are required to designate varietiesand to indicate origin. The most important hop-producing countries, together with their quanti-ties harvested, are listed in Chapter 6. Hops canbe judged on the basis of manual classification(appearance, color, pest infestation), whereasbrewing values can only be determined by chem-ical analysis. Table 3 lists the most importantcomponents found in hops. The bitter acids (α-and β-acids) and the aroma substances (hopoils)are of great importance both from the viewpointof brewing technology and for the taste of thebeer.

Table 3. The chemical composition of hops (mass fraction in %)

As is Dry matter

Water 9 – 12α-Acids 2 – 17 2.2 – 13.5β-Acids 2 – 10 2.2 – 11.2Hop oils 0.5 – 2.5 0.6 – 2.8Non-nitrogen extractcompounds

4 – 9 4.5 – 10

Protein 15 – 21 13 – 22Fiber 10 – 17 11 – 19Polyphenols 3 – 8 4.5 – 16Minerals 7 – 11 8 – 12Lipids and waxes up to 3 up to 3.4Fatty acids 0.05 – 0.2 0.06 – 0.22

2.2.1. Resins

The bitter constituents of hops consist ofα-acids(humulones), β-acids (lupulones), soft resins,and the oxidation products of bitter acids, calledhard resins. The brewing value of the individualfractions varies and depends on their solubilityin beer andwort and on their bitterness potential.

The α-acids are the most important of thesebitter components because of their high bitter-ness potential.

The soft resins produce a lower bitternesslevel, about 10 – 33 % of the intensity producedby humulones. Hard resins are even less bitter.The β-acids are not bitter at all. The solubility oftheα-acids is very dependent on the pHvalue.Atthe pHof thewort, these substanceswill dissolveto only a limited degree. In beer itself, α-acidsare found only in very limited quantities, be-cause they are isomerized during the boiling pro-cess whereas the remaining acids are removedduring fermentation as part of the foam cover.The α-acids isomerize to iso-α-acids, e.g., cis-and trans-isohumulone. All α-acids and theirisomerization products have approximately thesame bitterness.

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The isomerization products are significantlymore soluble than the original α-acids, andare stable at the pH value of beer. Duringthe isomerization process the following α-acidderivatives also are formed: cis- and trans-alloisohumulones, abeoisohumulones (oxidizedisohumulones), antiisohumulones, spiroisohu-mulones, humulinic acids, and their various ho-mologues; for details, see [2].

The lupulones (β-acids) are insoluble at thenormal pH value of the wort. They do not iso-merize during boiling, and are largely removedwith the spent hops and the trub without beingutilized. Lupulone differs from humulone by aside chain on the C3 of the six-membered ring,and gives rise to the same homologues as humu-lone.During storage, lupulones oxidize toβ-softresins, which are soluble in the wort and in beerand also impart bitterness to the latter.

2.2.2. Hop Oil

The volatile and nonvolatile aromatic compo-nents of hops also determine hop quality. Thearomatic content of hops is influenced not onlyby the variety but also very much by the dryingand storing conditions and by processing.

The relative amounts of the almost insolublesesquiterpenes, such as humulenes, farnesenes,andβ-caryophyllenes, can be used to distinguishbetween the different varieties.

The mono- and sesquiterpenes become moresoluble by oxidation, i.e., they are converted toepoxides; during fermentation they are partlytransformed by the yeast to the correspondingsesquiterpene alcohols and can therefore con-tribute to the aroma of the beer.

Some volatile compounds (aldehydes, ke-tones, alcohols, and esters) are also producedduring aging of the hops by side-chain break-down of the bitter acids. Most of these, however,evaporate during wort boiling.

2.2.3. Polyphenols

Hops contain a number of phenolic componentsand derivatives of low molecular mass, such asphenolic acids (e.g., p-hydroxycoumaric, gallic,ferulic, protocatechinic, and caffeic acid), color-ing components (catechins, flavones, and antho-cyanidines), and polycondensated substanceswith strong tanning properties, which can origi-nate from procyanidines. Hop polyphenols playa role in the establishment of the intrinsic col-loidal stability of beer [21], [22]. The net resultof boiling is a dramatic change in the alreadycomplex polyphenol composition of wort. Partof the complexity can undoubtedly be ascribedto the ready oxidation and the ease of polymer-ization of many polyphenols. Most of the hoppolyphenols are removed during wort boilingby precipitation with proteins. The addition ofhop polyphenols does not alter the foam consis-tency and color of beer, but very high dosages ofhop polyphenols and long boiling times may ad-versely affect the colloidal stability. Lowmolec-ular mass polyphenols act as antioxidants andhence have a beneficial effect on beer flavor sta-bility. The positive effects of lowmolecularmasspolyphenols on human health are reported inChapter 7.

2.2.4. Processing of Hops and Hop Products

After harvesting, the hop cones must be driedfrom a moisture content of 75 – 80 % to a levelof 10 – 12 % using low temperature and strongair circulation. The hops are sulfurized beforebeing packed into bales or compressed into bal-lots. Hops should be stored in cool, dry, darkareas at about 0 ◦C to preserve their quality. Vac-uum packing followed by impregnation with aninert gas is necessary if prolonged storage ofthe hopproduct is anticipated.High temperature,oxygen, moisture, and light will cause changesin the oil fraction of hops; bitter acids becomeresins and lose part of their bitterness potential,whereas the polyphenols transform into highercondensed products [32–34].

Various hop products find acceptance nowa-days in the brewing industry because of theirimproved storage capacity, longer preservation

8 Beer

of quality, and simpler handling in the brewery.Regulations control the use of these products invarious countries. Hops products can be classi-fied into four general types:

Non-Isomerized Hop Products. In thistype of product the α-acids remain unchangedduring hop processing. To achieve sufficient iso-merization during wort production they must beadded to the kettle at the start of or during wortboiling. Products included in this category are:Double compressed whole hopsHop pellets type 90. By drying hops down toa moisture content of 6 – 9 % and grinding,a powder is obtained. The powder is usuallypelletized and packed under inert conditions.Because these pellets possess a larger surfacearea, their components are more readily sol-uble than those from raw hops. Therefore,the use of hop pellets type 90 offers savingsof 10 – 15 % in terms of α-acids. Pellets alsooccupy a considerable smaller volume thanraw hops.Hop pellets type 45. After drying, hops aredeep-frozen to about – 30 ◦C and ground.Lupulin is separated from the cones and fromother nonessential parts of the leaves by siev-ing at the same low temperature. This treat-ment also reduces the polyphenol concen-tration in the resulting hops, depending onthe extent of removal of nonessential com-ponents. Furthermore, the content of unde-sired components such as nitrate or pesti-cides is reduced. The powder, which usuallyis pelleted, offers savings in terms ofα-acidsof about 15 % when compared with naturalhops.Stabilized hop pellets are produced by blend-ing magnesium oxide or calcium oxide withthe hop powder prior to pelletization. Duringthe formation of the pellet, the α-acids reactwith magnesium ions to form salts, whichisomerize to iso-α-acids during storage.Hop Extracts. Solvents used for the extrac-tion of hops include ethanol and carbon diox-ide (supercritical or liquid). For the pro-duction of the extract the hops are ground,the valuable components are dissolved, andthe solution is separated from the solid sub-stances. In all production methods, the sol-vent is finally evaporated at 40 – 60 ◦C andreclaimed. The extracts are packed in cans.

Carbon dioxide and ethanol dissolve the α-acids quantitatively. During extraction with90%ethanol, isomerization of 10%of theα-acids takes place. Carbon dioxide dissolvesonly traces of the hard resins under the pre-vailing extraction conditions for the removalof bitter substances.The aroma-contributing components arequantitatively dissolved; losses causedby theevaporation of the solvent are minimal in thecase of carbon dioxide and substantial withethanol. In the process employing supercrit-ical carbon dioxide, the extraction condi-tions are controlled by pressure and tempera-ture. The composition of the resulting extractof aroma-contributing substances and resinscan be controlled by fractionation.Carbondioxide does not dissolve tannins andhop proteins. These may be obtained duringa secondary extraction step by the use of hotwater. During one-step procedures using eth-anol as solvent, a certtain proportion of tan-nins also is extracted, which can easily beremoved by centrifugation.All extract can be standardized to a definedα-acid content with hot water extracts ofhops or glucose syrup. The savings in bittersubstances when using extracts are aprroxi-mately 10 % in terms of the amount of theα-acid.

Isomerized Hop Extracts. In these prod-ucts, α-acids have been isomerized to iso-α-acids during processing. Unlike α-acid basedproducts, iso-α-acid products can be added ei-ther during wort boiling or after fermentation,depending on the composition of the product.Isomerized hop products include:

Isomerized Hop Pellets. The α-acids of sta-bilized hop pellets are converted easily andquantitatively into the corresponding iso-α-acids by heat treatment at temperatures be-low 60 ◦C.Isomerized Kettle Extracts. There are twobasic methods for the production of iso-merized kettle extracts. In the first methodpure resin extract is heated in contact withaqueous potassium carbonate-hydroxide so-lution. This gives an isomerized kettle ex-tract in which the iso-α-acids are present as

Beer 9

potassium salts. In the second method thepure resin extract is mixed and heated withmagnesium oxide. No water is added dur-ing the isomerization process. In the mag-nesium salt form the extract is very viscousand not easy to handle. By treatment with astrong acid, the magnesium iso-α-acid saltsare converted to the free acids. This extractcan be handled similarly to a conventionalpure resin extract.Isomerized hop extract is used for dosinginto cold, fermented beer and must thereforebe of high purity and essentially free of in-soluble hop resins.Reduced isomerized hop extracts comprisethree different reduced forms of iso-α-acids: extracts containing rho-iso-α-acids(dihydroiso-α-acids), those containing tetra-hydroiso-α-acids and those containing hexa-hydroiso-α-acids.

Hop oil products are specifically used toimpart aroma to beer. They include the followingpreparations:

Hop pellets type 100 are produced by simplecompression of whole hops. Waste materialsare removed, but the hops are not dried ormilled prior to compression. The pellets arevacuum packed in order to preserve the qual-ity of the oil during storage. Whole hop pel-lets are generally added to cask conditionedales in order to impart the beer ‘dry hop’aroma.Oil-Rich Hop Extract. An extract, that hasa higher than normal oil content, can beobtained by partial extraction with carbondioxide or fractionation during productionof pure resin extract with supercritical car-bon dioxide or by addition of pure hop oil topure resin extract.Pure Hop Oil. A common method for isolat-ing pure hop oil is a steam distillation of anextract under vacuum or atmospheric pres-sure.Hop oil emulsionsFractionated hop oils

Miscellaneous Hop Products. Specialtyhop products are available, which do not con-tribute significantly to beer bitterness, but areused instead to prevent overfoaming in the kettle

and ensure normal fermentation characteristics.These products include:

Base hop extractsPurified β-acid fractions

2.3. Brewing Water

Natural water always comes as a highly dilutedmineral salt solution; its chemical compositionand the concentrations of various constituentsusually are determined by the geology of thespecific region of origin. In addition, impurities,organic substances, and organisms may subse-quently enter the water. Because of their lowconcentration, the salts are almost completelydissociated into ions, which indirectly influencethe quality of the beer.

Today almost any water can be made suit-able for brewing but at a corresponding cost.Expensive water treatment is unavoidable if cer-tain ions are present in such high concentrationsas to be detrimental to the beer, e.g., an exces-sive amount of sodium chloride or more than30mg/L of nitrate ions.Nitrate is reduced duringfermentation to nitrite, which is toxic to yeasts.

2.3.1. Salts

The total solids content of natural water usu-ally is 50 – 2000mg/L, with an average of ca.500mg/L.The following ions are predominantlyfound in the water:

Cations: H+, Na+, K+, NH+4 , Ca

2+, Mg2+,Mn2+, Fe3+, Al3+

Anions: OH−, Cl−, HCO−3 , NO−

3 , NO−2 ,

CO2−3 , SO2−

4 , SiO2−3 , PO3−

4Calcium and magnesium salts are most com-

monly found in natural waters. The sum of thesetwo cations determines the total hardness of thewater, which is expressed in milliequivalentsper liter (mval/L). Carbonate, hydrogencarbon-ate (HCO−

3 ), and free carbon dioxide have to becontrolled carefully because of the corrosive na-ture of free carbon dioxide. The non-carbonatehardness is accounted for by salts of acids otherthan carbonic, e.g., sulfates. These salts remaindissolved during boiling [35].

10 Beer

Effects During Mashing. At the concentra-tions of mineral salts normally found in water,interactionswith soluble components of themaltas well as various effects on the enzymes ofthe malt and on the ingredients derived fromthe hops are of practical importance, especiallywith regard to the net effect on the solubility ofthe α-acids. It is essential to observe how differ-ent ions present in the water, together with themalt ingredients, influence the pH values of themash, the wort, and the beer. The phosphates ofsodium, calcium, and magnesium are most ef-fective in this regard. Further reactants includethe potassium and calcium salts of such organicacids as lactic, malic, and succinic. The vari-ous hydrogencarbonates influence the acidity tovarying extents, because the solubilities of thecorresponding secondary or tertiary phosphatesare different. Accordingly, the effect of mag-nesium hydrogencarbonate is greater than thatof calcium hydrogencarbonate, because the sec-ondary magnesium phosphate will remain in so-lution. The effect of sodium hydrogencarbonateis even more marked, because strongly alkalinetertiary sodium phosphate is formed, which re-mains in solution together with the secondarysodium phosphate. In addition, the precipitationof phosphates by calcium and magnesium ionsresults in a decreased buffering capacity of themash, so that the pHmay drop too rapidly duringfermentation.

The alkalinity of thewort caused by hydrogencarbonates also affects the solubility behavior ofthe bitter substances present in hops. On the onehand, when the pH is increased, the solubility isincreased, but an unpleasant, harsh bitterness iscreated in the beer. On the other hand, the ionsof the alkaline-earth metals are able to compen-sate for the increase in pH caused by hydrogen-carbonate. The following equation demonstratesthis effect:

3 Ca2+ + 4 HPO2−4 →Ca3(PO4)2 + 2 H2PO

−4

Calcium ions convert the secondary phosphateto the acidic primary phosphate. Magnesiumions are only half as effective by comparisonwith calcium ions.

Alkalinity. The termalkalinity is used to des-ignate the concentration of the hydrogencarbon-ate ions in water (→Water, Chap. 6.1.). The

“residual alkalinity” is calculated by subtractingthe effect of the acidity-improving alkaline-earthions from the effect of the acidity-destroying hy-drogencarbonate ions:

residual alkalinity = total alkalinity−(Ca hardness

3.5+

Mg hardness7

)

Hardness is given in degrees German hardness(dH). The total alkalinity is equal to the hard-ness linked to the presence of hydrogencarbon-ate ions.

The residual alkalinity indicates the suit-ability of the brewing water for the variousvarieties of beer. The residual alkalinity forpilsener should be below 35 ppm CaCO3, and90 – 110 ppm CaCO3 for pale beer. Decreas-ing the residual alkalinity by 90 ppm CaCO3will lower the mash pH by 0.15 units. Shouldthe residual alkalinity increase substantially,considerable disadvantages can be expected.The brewhouse yield is reduced by 2 %when the residual alkalinity is in the range of180 – 210 ppm CaCO3. Similarly, high valuesfor residual alkalinity resulting in a mash pH ofover 5.8 will reduce the effectiveness of most ofthe hydrolytic enzymes. As already mentioned,a high pH value causes a molecular solution ofthe α-acids, which will impair the bitter flavorof the beer. The release of polyphenols from thehusks of barley malt will occur with greater easein this pH range, and is acceptable only in thecase of dark beer.

2.3.2. Brewing Water Treatment

Water used for brewing should correspond inquality to drinking water; it should be clear, col-orless, and neutral in taste and smell. It shouldnot contain heavy metals, especially iron andmanganese, and should not be corrosive. Naturalwaters originate from many different geologicalformations and therefore very rarely conform tothe quality required for brewing water. For thisreason treatment is required before water fromsuch sources can be used for brewing. The ac-tual extent of water conditioning is governed bythe concentrations of anions, the dissolved or-ganic substances, and the presence of aggressivegases in the untreatedwater. Processing of brew-ing water also depends on the specific needs of

Beer 11

the brewer and on the particular beer required.The selection of a treatment method also is in-fluenced by the prevailing laws.

Attention is directed to both the carbonatehardness and to the ratio of carbonate to non-carbonate hardness, which should be around 1 to2 – 2.5. Bearing profitability in mind, the treat-ment methods mentioned in the following canbe applied:

Heat Precipitation. Carbonates can be pre-cipitated by boiling. However, this method is noteconomical.

Decarbonation. The simplest procedure forthe precipitation of carbonates is to add milkof lime. The following components can be re-moved by Ca(OH)2: free CO2, Ca(HCO3)2,Mg(HCO3)2, and MgCO3. For the latter, how-ever, a pH of 10.5 – 11 is required. If the non-carbonate hardness in the raw water is higherthan the magnesium hardness, quick or pressuredecarbonation may be used. In this case, waterand milk of lime are intensively mixed in a re-action vessel, where calcium carbonate precipi-tates as a coarse product that sediments well.

Variations in magnesium hardness are moreproblematic. If themagnesiumhardness exceedsthe non-carbonate hardness, slimy magnesiumhydroxide will partly precipitate and clog thegravel filter bed; it can also contaminate thebrewing water. To overcome this problem, atwo-step precipitation – decarbonation processis used. In the first step, the calculated amount ofmilk of lime that is needed for the decarbonationand for the removal of magnesium is added to apartial stream of the rawwater (two thirds). Thisis done in a superliming reactor, where both cal-cium carbonate and magnesium hydroxide areprecipitated. This alkaline water subsequentlyreacts with the remaining one third of the rawwater stream in a refining reactor. In this reac-tor, the excess lime is used to precipitate calciumcarbonate whereas the magnesium carbonate ofthis 30 – 40 % stream remains in solution. Thetotal water is finally collected in a storage tankafter filtration through a gravel bed.

In order to control variability in the composi-tion of raw water hydrogen ion exchange facili-ties can be installed at the end. This equipmentwill automatically be activated whenever the pHrises above a predetermined value. The proce-

dure ensures extensive removal of the magne-sium hardness. The brewing water thus obtainedis very poor in carbonates, and does not containan excess of free carbon dioxide after irrigation.

Ion Exchange (→ Ion Exchange). Brewingwater can be readily deionized by using ion ex-change resins, which require little space and fa-cilitate a quicker throughput. The availability offood-grade ion exchange resins enables raw wa-ter to be processed to give water of any desiredcomposition.

Cation exchangers can be either weakly orstrongly acidic, depending on the anticipatedload.Weakly acidic exchangers remove only thehydrogencarbonates (of Ca2+ and Mg2+) fromthe rawwater.During this process a large amountof free, corrosive CO2 is liberated; this needsto be removed by blowing a countercurrent ofair through the water. The remaining CO2 reactswithmilk of lime ormarble to formCa(HCO3)2;in thisway slight hardening is achieved.Alterna-tively, the deionized water can be blended withraw water.

Strongly acidic ion exchangers operate in asimilar manner. All cations are removed fromthe rawwater, even those of the strong acids, andare replaced by hydrogen ions. These exchang-ers are especially effective with hardness causedby magnesium. The free mineral acids that arethus formed are neutralized with saturated milkof lime.

Anion exchange: SO2−4 , Cl−, and NO−

3 ionsmaybe removedwith anion exchangers; thiswilldecrease non-carbonate hardness. Even thoughtotal deionization is not desirable in the produc-tion of brewing water, complete ion exchangeenables the brewer to prepare brewing waterfrom sources with widely differing composi-tions.

Electroosmosis. For total deionization byelectroosmosis, investment and operating costsaremuch higher than in the treatment proceduresdescribed above. In addition, this proceduremaybe applied only if combinedwith other deioniza-tion methods. In a continuous-current field thesalts in the water migrate towards the electrodes,which are separated by membranes. The watertrapped between the membranes is appreciablylower in its salt content and can be run off.

12 Beer

Reverse Osmosis. Ions, molecules, andother small particles can also be removed fromwater by reverse osmosis. Additionally, tablewaters may be obtained from the resulting con-centrate by proper sterilizing and carbonatingprocedures, provided that the ionic compositionis appropriate.

Acid Addition. The addition of mineralacids, such as hydrochloric, sulfuric, or phos-phoric acid, changes the carbonate hardness intonon-carbonate hardness, but the total hardnessremains unaltered.

Other Processes. Another important treat-ment may become necessary if bad-smelling orbad-tasting substances have to be removed. Thiscan be achieved by installing an activated carbonfilter upstream of the deionization equipment.Suspended matter is removed with flocculantsand gravel bed filters, so as to avoid clogging ofthe downstream equipment.

Furthermore, such mineral salts as are foundin natural water may be added to brewing wa-ter. Acceptable food-grade salts are: CaCO3,MgCO3, CaCl2, CaSO4, and NaCl.

2.4. Beer Yeasts

Brewery yeasts belong to the family of Sac-charomycetaceae and the genus Saccharomyces.They have the main advantage that their cellspropagate by budding. For the production ofbottom-fermenting beers, Saccharomyces carls-bergensis are used, and for top-fermenting beers,Saccharomyces cerevisiae [36].

After the malt enzymes have been destroyedduring wort boiling, the yeast provides the orig-inal wort with its enzyme system. Wort is not anideal nutrient medium for yeast. In order to me-tabolize actively, the yeastmust synthesize thosesubstances it needs according to thewort compo-sition. Depending on the syntheses required, theamounts of themetabolic products that are foundin the fermenting substrate will differ. Refer-ences to taxonomic and technological structure,morphological characteristics, chemical compo-sition, propagation, metabolism, and yeast en-zymes can be found under the appropriate key-words: → Ethanol, Chap. 5.1.; →Yeasts.

The pitching yeast should be selected as care-fully as the other raw materials. Furthermore,its introduction into production, its crop afterfermentation, and its further handling should bemanaged with great care. Short-term storage ofyeast and aeration before pitching retains fer-menting power and keeps the yeast in good phys-iological condition. If an infection with organ-isms detrimental to beer occurs, the yeast mustbe removed quickly from the production process

2.5. Auxiliary Materials and BrewingAids

This group comprises all those chemicals thatcome into contact with the raw materials, thewort, and the beer; they are not essential for theproduction of beer, and are used for the correc-tion of deficiencies. No general directions existin the various countries where beer is brewedregarding the use of these materials.

Malting Auxiliaries. Various chemicalsmay be added to the steeping water. Hydro-gen peroxide decreases the sensitivity of barleyto water, and reduces the danger of mold for-mation. Alkaline additives, such as Ca(OH)2 orNaOH, will increase the leaching out of husktannins.

Gibberellic acid is an effective growth agent;it stimulates enzyme formation and acceleratesgermination. The amount of growth factor that isto be added to the final steepingwater should notexceed 0.05 – 0.1mg/kg of barley because of thedanger of overmodification and additional col-oration.

In order to avoid excessive losses of extractduring germination, it is possible to add growthinhibitors during the later stage of germination.For this purpose, dilute nitric acid, formalde-hyde, or, most commonly, potassium bromateare used.

Sprinkling the green malt towards the end ofthe germination phase with an aqueous glucosesolution will increase the amount of extract to agreater extent than would be expected from theamount of sugar used.

The addition of sulfur dioxide to the air flowduring kilning will result in a lighter color anda higher extract yield by lowering the pH value.

Beer 13

Other aids to water treatment are described inSection 2.3.

Brewhouse Auxiliaries. The first concern ofthe brewer is to eliminate differences in qual-ity of the raw materials which have remainedthrough insufficient modification in the malt-house and which could not be compensated forduring mashing. These cytolytic, proteolytic,and amylolytic deficiencies, or the use of an ex-cessively high proportion of adjuncts, will becompensated in the mash by adding enzymepreparations that originate from sources otherthan malt. The hard, raw aftertaste that fre-quently occurs in such beers can be reduced byadding mineral acid (HCl, H2SO4, H3PO4) orconcentrated lactic acid to the mash.

During wort boiling, protein-precipitatingsubstances such as formaldehyde, tannin, car-rageenan (Irish moss), or protein-stabilizingsubstances may be added in order to improvethe clarification process and stability of theend product. The addition of cross-linked poly-vinylpyrrolidone (polyvinylpolypyrrolidone;PVPP) reduces the polyphenol concentration.Synthetic additives based on polyester result ina compact separation of the unpleasant, coarse,and bitter-tasting hot trub.

Numerous advantages can be gained by us-ing a lactic acid culture propagated in the brew-ery (biologic acidification). The lactic acid bac-teria obtained from malt ferment at 45 – 47 ◦Cin 10 – 12 % unhopped first wort, and producelactic acid (concentration 0.8 – 1.2 %) within12 – 20 h. The culture is added in the brewhouseduring mashing or wort boiling to obtain the de-sired pH value.

Fermentation and Maturation Aids. Defi-ciencies in yeast nutrients can be counteractedby the addition of yeast food, which containsamino acids, minerals, vitamins, and zinc salts,to the substrate in order to achieve a vigor-ous fermentation. Because all enzymes of themalt are denatured during wort boiling, onemay wish to add enzymes with a wide activ-ity spectrum, which may additionally enhancethe clarification and filtration of the beer in thefermenting room. This will become necessaryif the naturally-occurring enzymes achieve an

insufficient hydrolysis of malt components witha high molecular mass.

If foam production is impaired by this enzy-matic action, which is rather difficult to control,foam stabilizers (alginates, poly(propylene gly-col), or polysiloxane) can be added.

After fermentation, bacterial 2-aceto-lactatedecarboxylase may be added to the fer-mentation substrate, which will transform di-acetyl directly to acetoin (see Section 3.3.2). Inthis way the maturation rate can be increasedconsiderably.

Antifoaming agents based on silicones havecome into use in order to reduce the headspaceneeded during warm fermentation in tall, cylin-drical vessels. A small amount (4 – 8 g/hL) ofthese agents is sufficient to prevent the forma-tion of a fermentation cover. The foam inhibitoris removed completely by kieselguhr filtration,so that the final foam quality of the beer will notbe impaired.

Clarification Aids. Before bottling, the beeris filtered through a filter cake. Proven materialsfor this purpose are kieselguhr (mud-free, cal-cined and screened diatomaceous earth) of var-ious particle size distribution, or perlite (groundand calcined glassy rock of volcanic origin.

Activated carbon may be used to correct amild off-taste; it is usually used in the treatmentof rest beers. Shortly beforefiltration, hydro- andxero-silica gels may be added, which selectivelyaffect the highmolecularmass nitrogen fraction,and which also contribute to the build-up of thefilter cake.

Stability Improvers. The stability of beer isdefined as the ability to preserve its charac-teristics from bottling to consumption. To en-sure an adequate biological stability in zones ofmoderate climate it is sufficient to clarify thebeer through kieselguhr and sheet filters, pro-vided that the beer is delivered to the consumerquickly.

Higher demands can only be met either bythe use of insoluble substances which act me-chanically or adsorptively, or by pasteurizing thebottled beer (with 12 – 14 pasteurization units),or by hot bottling at 68 – 75 ◦C. However, heattreatment results in early aging of the beer. Oxy-gen trapped during filling reacts quicklywith thebeer. As a result a nonbiological haze may form

14 Beer

sooner or later. This is derived either from tan-nins or from proteins. Tannins may be removedby adsorption onto polyvinylpolypyrrolidone,or by precipitation with formaldehyde. Haze-forming protein particles may be removed withsilica preparations or bentonite. Proteolytic en-zymes, such as papain, bromelain, or ficin, de-compose high molecular mass proteins to non-hazing components.

During the breakdown of proteins, two char-acteristics, stability and foam, again run counterto each other. Metal ions accelerate haze forma-tion; they can be complexedwith ethylenediami-notetraacetic acid.

During long-term storage beer becomesvulnerable to other dangers including flavorchanges, particularly through oxidation, differ-ent climatic and mechanical conditions, and ef-fects due to light. The most effective remedyis low-oxygen bottling; if this is not possible,the beer needs to be protected against oxidationby the addition of such antioxidants as ascorbicacid, sulfites, sugar reductones, or by enzymessuch as glucose oxidase or catalase. The influ-ence of oxygen during bottling can also be over-come by evacuating the bottles, by pressuriz-ing the bottleswith fermentation carbon dioxide,and by allowing fobbing. For additional safetythe cleaned beer barrels, kegs, or bottles canbe treated with peracetic acid or other productsbased on hydrogen peroxide, iodine-releasingchemicals, or sulfur dioxide.

3. Production Technology

3.1. Malting

Malting is defined as allowing grain to germi-nate under well-controlled conditions. Themainpurposes of malting are the development of en-zymes in the grain with simultaneous degrada-tion of high molecular substances in the cellwalls (modification), the achievement of a dis-tinctive character by color and aroma com-pounds, and removal of undesired aroma com-pounds (i. e. S-methylmethionine and dimethylsulfoxide). High extract yield and low maltingloss are economic goals. The schematic proce-dure of malt production is shown in Figure 1. Figure 1. Flowsheet of malt production

Additives that are shown in dotted ellipses are not necessary

Beer 15

Figure 2. Steeping

After thorough cleaning with various separa-tors and grading machines, the brewing barleyis dried to a moisture content of ca. 12 %, whichallows storage without damage to the embryo. Ifproper drying equipment is not available, cool-ing of the barley can help prevent its spoilageto a certain extent. Before malting is actuallystarted periodic aeration is necessary to removethe carbon dioxide emanating from the grains,so as to keep the germinating facilities healthyand to maintain germinative ability.

3.1.1. Steeping

Upon addition of water germination of the grainbegins. No particular requirements are placed onthe steeping water during malting, but it shouldbe of potable quality. In the beginning the wateruptake is an osmotic process and depends onwa-ter quality and temperature. The grains begin torespire. Respiration is continued during the en-tire steeping period. At 30 % moisture contentthe water is taken up via the micropyle (physio-logical process) and living tissue in the embryois formed.

Steeping Equipment. The round or rectan-gular steeping drums with conical bottoms (ca-pacity 2.2 – 2.4m3 per ton of barley) must beequipped with a water inlet and outlet, dischargevalves, overflow for floaters, a carbon dioxide

exhaust vent, and an air inlet for pressure aera-tion and recirculation. Recirculation pumps andsprayers are optional. The first cleaning is oftenperformed in washing drums.

Steeping Technology. Rapid water uptakeand enhanced germination is possible in pneu-matic steeping, inwhichwet steeping periods al-ternate with extended dry steeping periods (thelatter during 50 – 80 % of the total period). Firstof all, steeping provides a definite moisture con-tent appropriate to the physiological characteris-tics of the barley. During subsequent dry steep-ing (16 – 24 h) at a moisture content of 30 % thewater sensitivity of the barley declines.After fur-ther increasing the moisture content to 38 %, auniform germination of the kernels can be ex-pected within a period of 14 – 20 h. The mois-ture content is then raised to the final level inthe germination box by adequate spraying. Anexample of the steeping procedure and the nec-essary handling involved is shown in Figure 2.

When the temperature is raised from one wetsteeping period to the next, the temperature ofthe steeping materials is taken into account. Thecasting of steeped barley at 18 ◦C permits theuse of a germination procedure with decreasingtemperature as shown in Figure 3. Other steep-ing methods exist based on similar principles:the flushing procedure, the resteeping proce-dure, and the water-saving spray steeping.

16 Beer

Figure 3. Germination

3.1.2. Germination

Germination is a physiological process dur-ing which the embryo develops rootlets andacrospire. During this process, the nutrientsstored in the endosperm are partly consumed.The aim of controlled germination is to producea green malt of a definite composition, but notto allow the development of a new plant.

Germination Conditions. Germinationtakes place only under appropriate conditions inorder to achieve the desired metabolic changesduring the time necessary for germination. Pa-rameters are: moisture, temperature, ratio of airto carbon dioxide, and time. Steeping and ger-mination conditions have to be adapted to barleyvariety, harvest year, water sensitivity, vitality,and furthermore to the protein content and theexpected structure of the endospermmatrix. Themoisture content must not decrease during theentire germination period. Temperatures favor-able to uniform germination range from 14 to18 ◦C.

A sufficient supply of air must ensure bothnormal respiration and removal of carbon diox-ide. Germination will manifest itself first in no-ticeable changes in the appearance of the ker-nel. After “chitting” (breakthrough of the root-let), the rootlet divides into a main root and sec-ondary roots (forking). The acrospire also breaks

through the aleurone layer and pericarp, and be-gins to growunder the husk towards the tip of thekernel. During malting the development of thegerm buds is desirable only to a certain degree.

Besides these manifestations of growth,chemical transformations occur in the en-dosperm; stored materials are broken down byenzymes and changed into soluble matter. Theseare either used as an energy supply, or are builtinto new tissue in the germ buds. The growthfactors which develop during germination causethe formation of a number of enzymes in thescutellum and the aleurone layer.

Enzyme Formation. In addition to certainmodifications to the substances of the barley,the main purpose of malting is the induction andincrease in hydrolytic enzymes. The most im-portant groups of these are: hemicellulases, pro-teolytic enzymes, amylases, and phosphatases(see Table 4). Of the cytolytic enzymes, whichbreak down the hemicelluloses to lowmolecularmass materials, the β-glucanases are consider-ably more effective than the pentosanases. Thedegree of cytolysis may be determined empiri-cally by the continuous increase in friability ofthe endosperm; analytical measurements of thedifference between coarse and fine grind extractand the viscosity of the congress wort can bemade. Excellent cytolysis is achieved under con-

Beer 17

Table 4.Malt enzymes and their behavior during mashing

Enzyme CAS registry E.C. number Optimum conditions in mash Inactivation

number temperature,pH t, ◦C ◦C

OxidoreductasesPeroxidase [9003-99-0] 1.11.1.7 40 – 50 65Lipoxygenase [9029-60-1] 1.13.11.12 6.5 40 70Polyphenoloxidase 1.14.18.1 60 – 65 80

HydrolasesLipase [9001-62-1] 3.1.1.3 6.8 35 – 40 60Acid phosphatase [9001-77-8] 3.1.3.2 4.5 – 5.0 50 – 53 70α-Amylase [9000-90-2] 3.2.1.1 5.6 – 5.8 70 – 75 80β-Amylase [9000-91-3] 3.2.1.2 5.4 – 5.6 60 – 65 70endo-β (1→ 4)-Glucanase [9074-99-1] 3.2.1.8 4.7 – 5.0 40 – 50 55Cellulase [9012-54-8] 3.2.1.4 4.5 – 5.0 20 20Laminarinase [9025-37-0] 3.2.1.6 5.0 37 50Limit dextrinase [9025-70-1] 3.2.1.11 5.1 55 – 60 65Maltase [9001-42-7] 3.2.1.20 6.0 35 – 40 40β-Mannosidase [9025-43-8] 3.2.1.25 3 – 6 55 70Invertase [9001-57-4] 3.2.1.26 5.5 50 55exo- and endo-Xylanases 3.2.1.37 5.0 45endo-β-(1→ 3)-Glucanase [9044-93-3] 3.2.1.39 4.7 – 5.0 40 – 45 55exo-β-Glucanases 3.2.1 4.5 40 40Pullulanase [9012-47-9] 3.2.1.41 5.0 – 5.2 40 70Arabinosidase [9067-74-7] 3.2.1.55 4.6 – 4.7 40 60β-Glucan-solubilasewith esterase activity 3.2 6.6 – 7.0 62 73with carboxypeptidase activity 3.4 4.6 – 4.9 62 73

Aminopeptidases 3.4.1 7.2 40 – 45 55Carboxypeptidases 3.4.2 5.2 50 – 60 70Dipeptidases 3.4.3 7.2 – 8.2 40 – 45 55Endopeptidases 3.4.4 5.0 – 5.2 50 – 60 70

ditions of high moisture, average temperaturesof up to 18 ◦C, plenty of oxygen, and long ger-mination periods. Before the cell wall is brokendown, proteins must be hydrolyzed to a certainextent by proteolytic enzymes. The proteolysisis favored by high moisture content, low tem-perature, and an optimum germination period; ifgermination periods are too long, low-molecularprotein substanceswill be consumed for the syn-thesis of the rootlets and the acrospire. Themod-ification of the proteins can be quantified by thedegree of protein hydrolysis (ratio of soluble ni-trogen to total nitrogen) and by the total amountof soluble nitrogen.

The protein content of barley decreasessomewhat during germination, because theprotein-rich rootlets are removed after kilning.The modification of starch by the action of α-and β-amylases occurs to only a moderate de-gree. The liberation, activation, and formation ofthe β-amylase, as well as the de-novo formationof α-amylase during the germination process,are both important. α-Amylase can be formedonly in the presence of oxygen; its production is

favoredby ahighmoisture content duringgermi-nation, low germination temperatures, and longgermination periods.

Germination Technology Practice. Thecontrol of the batch is governed by the maltingsystem, and is also determined by the steepingmethod and by casting. Germination with in-creasing temperature proceeds between 12 and16 ◦C; for barley grown in hot, dry climates, thetemperature may rise as high as 20 ◦C towardsthe end of germination. Slow but even growth,slow enzyme formation, and low enzyme activ-ity characterize the germination process. Greenmalts are sometimes kept warm during the last24 h of the germination period in order to attainthe desired extent of cytolysis.

During germination at constant temperature,respiration and temperature increase are facili-tated; this results in a more active metabolismand in strong growth. Maintaining the grain bedat 14 – 15 ◦C results in most even modification.

With modern steeping and germinationequipment it has become common practice togerminate with decreasing temperature (Fig. 3).

18 Beer

The relatively warm initial germination phase ata still low moisture content favors quick hydrol-ysis and high enzyme activity. Enzyme forma-tion is further stimulated by quick cooling of thegrain bed and a simultaneous increase in mois-ture content. Because of the high moisture level,modification occurs satisfactorily in spite of thelow temperature. The embryo tries to maintainits original growth rate, and compensates for theimpaired living conditions by increased enzymeformation.

In the steep tank and during the early “bi-ological” phase of germination, sufficient oxy-genation of the grain bed is necessary for theformation of endo enzymes. In the subsequent“modification phase”, a moderate increase ofcarbon dioxide in the grain bed (up to 4 %) willinhibit too vigorous growth and improve cytol-ysis. Germination usually takes six days. Thedifferent modification properties of the varioustypes of malt can be compensated by varying thegermination parameters, especially the moisturecontent.

Malting Equipment. Floor malting is theoldest and simplest malting method, but it isfound only very rarely today. The metabolic ac-tivity of the steeped grain,which has been spreadon the floor, is controlled by the temperatureof the room, by the height of the grain bed,and by turning. The temperature is allowed torise steadily from the “young pile” through the“growth” and “matting pile” up to the “old pile”.

Allmethods that use aeration (pneumatic sys-tems) are characterized by malting in deep beds.The most important and most difficult task inthis type of malting is the constant maintenanceof effective cooling of the grain bed by meansof an air stream saturatedwithmoisture. Besidessupplying oxygen and removing carbon dioxideresulting from respiration, the air stream mustalso inhibit excessive loss of water during ger-mination. This is not easy to accomplish becausethe air in the grain bed warms up, and there-fore removes moisture. Each pneumatic germi-nation facility consists of aeration installationsequipped with temperature control and moistur-izing capabilities, ducts for fresh air, exhaust air,and recycled air, and fans. In addition the germi-nation box is fitted with perforated floors, turn-ing and spraying devices, and with dischargingequipment.

The various pneumatic malting installationsoriginate from drum or boxmalting. Drummalt-ing is practically only to be found in the var-ious forms of the Galland drum, or maltingbox drum. Box malting, with the further de-velopment of tower malting or moving grainbed (Wanderhaufen), is almost the only methodthat has survived. The specific load of a boxis 350 – 500 kg/m2; this corresponds to a depthof the green malt bed of 0.7 – 1.25m. Amongthe special malting systems, either the combinedgermination – kilning systemormalting systemswhere steeping, germination, and kilning occurin one combined installation are used in practice.

3.1.3. Kilning

In order to stop the chemical and biologicaltransformations that take place during germina-tion, the greenmalt is dried by kilning. This pro-cedure yields a storable product. Another func-tion of kilning is to remove the vegetable-likeflavor of the green malt and to impart to thekilned malt a specific aroma and a defined colorcharacteristic for the type of malt required. Fi-nally, the rootlets, which are very much valuedas nutritional feed for cattle, are also removed.

The control of drying processes (witheringand kilning), together with the quality and mod-ification of the green malt, determine the char-acter and color of the product.

Drying and Kilning. Moist green malt isvery sensitive to high temperature. In order tomake allowance for this sensitivity, whitheringis carried out at high aeration and low temper-ature. This step decreases the moisture contentfrom the green malt stage to the hygroscopicpoint (18 – 20 %).

Further drying is accomplished somewhatmore slowly, but is still relatively easy to han-dle up to the point of “breakthrough”, at whichthe temperature above the kiln floor is higherthan that of the wet bulb temperature. Break-through occurs when the moisture content is ca.10%.The subsequent dryingprocedure at highertemperature and low aeration becomes progres-sively more difficult, because the internal mois-ture must be conveyed from the interior of thegrain to the surface. The progress of whithering

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Figure 4. Drying and kilning of pale malt (single-floor kiln, no air recycling)

Figure 5. Drying and kilning of dark malt (single-floor kiln, air recycling)

and kilning for pale and dark malts in single-floor, high-capacity kilning equipment is shownschematically in Figures 4 and 5.

During the drying of malt the moisture con-tent, volume, weight, and color of the grainchange. The dehydration of the green malt low-ers themoisture content,which ranges accordingto the malting technique from 41 to 46 % (palegreen malt) and 48 to 50 % (dark green malt)initially, to 3.5 – 4 % for pale malt and 1.5 – 2 %for dark malt. Careful dehydration ensures thatthe original volume of the green malt remainsunaltered.

The chemical and biological changes encom-pass three stages with relatively different reac-tions: natural growth, breakdown, and build-up.The formation of aromatic and colored com-

pounds is most important (Maillard reaction).During initial drying most enzyme levels in-crease and then decrease during kilning, depend-ing on the temperature [8].

Malt Kilns. During malt kilning the grainbed is aerated with drying air. The most primi-tive, directly heated, single-floor kilns were fur-ther developed to the indirectly heated double-floor and triple-floor kilns. Later single-floor,high-capacity kilns were built.

The combined germination – kiln boxes havea specific loading capacity of 420 – 500 kg/m2.Indirect heating systems, which keep the for-mation of N-nitrosodimethylamines (NDMA)on a low level, require big heating ovens withlarge heat-exchange surfaces. Theuse of recircu-

20 Beer

lated air offers various technological and energy-saving advantages. New methods use a thin ver-tical or horizontal layer and accomplish dryingin 8.5 – 9.5 h. The technique exposes practicallyevery grain to the desired kilning temperaturewithout causing any shrinking of the kernels.

After cooling the kilned malt, the rootlets areremoved, and the malt is polished. The maltshould then be stored before use in the brew-house for at least four weeks.

Malt Loss. The changes in weight and vol-ume occurring during steeping, germination,and kilning are shown in Table 5.

Table 5. Volume and mass changes during malting

Moisturecontent, wt %

Volume, hL Mass,kg

Malting barley 14 100 100Steeped barley 41 145 145Green malt 48 220 147Kilned malt 3.5 118 79Stored malt 4.7 120 80

The maltster is mainly concerned with thequality of the malt and the costs of an adequatebarley supply [37]. The production costs are alsoinfluenced bymalt loss. Loss arises during steep-ing, respiration, and germination, and amountsto 16 – 25 % (average 20 %) and 5 – 12 % (av-erage 8 %) on a dry-weight basis. For qualitycontrol standards, see [8] and [23].

Special Malts. Wheat malt is produced ac-cording to the processes followed for barleymalt. Chit malt and short-grown malt are ex-posed to short germination periods and have alow degree of modification. Caramel malt ismade from kiln malt by resteeping and roasting;kiln malt is converted to black malt by roastingat a temperature as high as 220 ◦C and moistur-izing. Scalding malt is heated to 50 ◦C at the endof germination and is subsequently kilned. Acidmalt is enriched with lactic acid bacteria.

3.2. Technology of Wort ProductionThe high molecular mass substances of the maltand other adjuncts must be solubilized by grind-ing and mashing. The extract solution is subse-quently separated from the solids by lautering.The lautered wort is then boiled with hops, clari-fied, and cooled. The basic procedures are shownin Figure 6.

Figure 6. Flowsheet of wort preparationAdditives that are shown in dotted ellipses are not necessary

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3.2.1. Grinding of the Malt

The manner in which this purely mechanicalprocedure is carried out is of critical importanceboth to the chemical and biological transforma-tions during themashing process and to the com-position and yield of the wort. The husks shouldbe crushed as little as possible in order to preventthe undesirable solution of tannins, bitter com-pounds, and coloring substances, which couldhave an adverse effect on the taste of the beer.Furthermore, the husks must serve the specificpurpose of forming a filter layer during lauter-ing when a lauter tun is used. In contrast, the en-dosperm requires fine grinding, because it con-tains the extract components that are to be dis-solved.

Nonuniform modification and the resultingdifferences in hardness of the individual partsof the malt grains cause the products of grind-ing to differ in size, extract yield, and ease ofbreakdown. Particles located at the tip of the ker-nel are undermodified; they are therefore toughand hard, and result in a coarse grind. The por-tion near the embryo is more friable, and yieldsa finely ground flour. Grinding also is the ba-sis for wort preparation, because the fineness ofthe grist determines the grist volume, which inturn determines the volume of the spent grains.During lautering of the wort, the technique ofsparging and raking depends on the character-istics of the spent grains (see Section 3.2.3 andFigure 9). The extent of modification and themoisture content of the malt, the mashing pro-cedure, and the lautering equipment determinethe degree of grinding. Proper sampling is mostimportant when particle size is assessed by siev-ing.

Gristing Mills. The grinding of malt is ac-complished by using smooth or fluted cast-ironrollers which rotate either at the same or at dif-ferent speeds relative to each other. The grindingprocess may be accomplished in one step, or insuch a fashion that certain particles are subjectedto repeatedgrinding.Accordingly, the number ofrollers ranges from two to six.

The simplest grinding equipment consists ofthe two-roller mill, which, however, can be usedsatisfactorily only on malt that is well modified.When four rollers are used, the two upper rollersfunction as crushers, whereas the lower rollers

accomplish the final grinding. Modern types ofmills use shaking screens after the first pair ofrollers; smaller particles and husks are thus re-moved, and only the harder coarse particles areground twice.

Mills with three passages adjust best to thevariations in malt quality. To obtain higher ca-pacities, five- and six-rollermills are exclusivelyemployed (Fig. 7). After crushing, the grist isseparated into three main fractions: husks, grits,and flour. The husks are directed to the two-huskrollers, where they are freed of the rough parti-cles clinging to them. The coarse grits from thefirst and second grinding are finally milled inthe grits roller pair. Mills with five rollers worksimilarly. Mills with several milling stages alsopermit removal of the husks, which are added tothe mash at a later stage of mashing. Condition-ing of the malt with low-pressure steam or warmwater (increasing thewater content by 1 – 1.5%)during multiple-roller milling proved advanta-geous. In this way, the husks remain elastic andare not destroyed even with thorough grinding.

Figure 7. Six-roller malt milla) Feed roll; b) Pair of precrushing rolls; c) Pair of huskrolls; d) Sieve box; e) Pair of grits rolls; f) Sampler

In wet milling the malt is steeped and thenground in simple double or quadruple rollermills; in the older systems this is accomplishedin one vessel, whereby a moisture level of about30 % is reached within 10 or 20min at a watertemperature of 50 ◦C or 30 ◦C, respectively. Inmodern systems, moisturizing is accomplishedby the use of a worm drive, giving a moisturecontent of 20 – 22 %.

22 Beer

3.2.2. Mashing

During mashing the solid particles are solubi-lized by the action of the brewing water and theenzymes formed during malting. The optimumconditions at which these enzymes act on theindividual compounds are shown in Table 4.

Starch breakdown is most important duringmashing. The solubilization of the starch gran-ules during mixing with water and heating pro-ceeds in various steps. After swelling of thestarch kernels, gelatinization of the starch oc-curs as the enzymatic hydrolysis starts. Starchhydrolysis is allowed to continue until no moreα-glucans (dextrins), which give a color withiodine, are present, and the desired attenuationlimit is achieved.

Protein hydrolysis is as important as starchhydrolysis, even though smaller amounts aretransformed. During mashing, numerous endo-and certain exopeptidases (carboxypeptidases)attack the proteins that were already extensivelymodified during germination. Depending on thedegree of protein modification, the enzyme con-tent of the malt, and the mashing conditions,peptides and amino acids are formed, as wellas proteinaceous substances of high molecularmass; the latter are responsible for foam, palatefullness, and nonbiological haze.

The hemicelluloses and gums are hydrolyzedduring mashing only after they have been re-leased at temperatures up to 50 ◦C. The β-glucanases are no longer active above this tem-perature, so that substances of high molecularmass that are released later during wort prepara-tion by the action of another enzyme cannot bebroken down any further. For this reason, uni-formity and extent of cytolytic modification isof greatest importance.

The acid phosphatases which occur in themalt hydrolyze the organic phosphates; duringthis process phosphoric acid is released, whichdecreases the pH value and increases the buffer-ing capacity of the malt, wort, and beer. Exces-sive buffering, however, attenuates the drop inpH during fermentation.

Increasing the temperature of the mash andthe duration of mashing increases the release ofpolyphenols and anthocyanidines.

Mashing Parameters. The amount of brew-ingwater used for dissolving the grist and for the

chemical and biological transformations consti-tutes themash liquor; spargings are used to yieldthe residual extract compounds, which remain inthe spent grains after lautering the first wort. Theamount of brewing water employed is basicallydifferent for all-malt pale and dark beers. Forpale beers, a greater volume ofmashing-inwateris chosen in order to obtain thinner mashes andto speed up the enzymatic processes. The vol-ume of brewing water is about 4 – 5 hL per 100kg of malt for pale beers, and 3 – 3.5 hL per 100kg malt for dark beers (mash rates 1 : 4 – 5 and1 : 3 – 3.5, respectively). The spargings (4 – 5 hLper 100 kg malt) must be added in such a man-ner that the remaining extract can be yielded ascompletely and quickly as possible. The last run-nings (end of spargings) should always be ana-lyzed for economic usefulness and beer quality(tannins, boiling time).

The intensity of the mashing process is de-termined by the mashing-in temperature. Tem-peratures of 35 – 40 ◦C facilitate solution of thesubstrate and the enzymes, so that these can bemore effective at their optimum temperature. Ataround 50 ◦C the breakdown of proteins, gums,and phosphates is increased; thoroughly modi-fied malts can be mashed in even at 62 ◦C, theoptimum temperature for β-amylase.

The dissolution of the ingredients of thebrewing materials is already initiated by grind-ing. Further parameters include the rest periodsat different temperatures, the pH value of themash, and the choice between decoction mash-ing (boiling parts of the mash) and infusionmashing (no boiling of mash portions).

Mashing Vessels. Formashing-in and for thestorage of partial mashes a heatable mash tun,equipped with an agitator, is used. In a similarmash kettle, which is usually smaller, the decoc-tion mashes are heated and boiled. In brewerieswith a two-vessel brewhouse, the lauter tun isalso used as mash tun, and the brewing kettle isalso used as mash kettle.

Mashing Procedure. The brewer deter-mines the composition of the various specificbeer types by the choice of the mashing proce-dure. All mashing methods can be derived fromthe three-mash decoction procedure shown inFigure 8. In two-mash procedures, one of thedecoction mashes is eliminated. Single-mash

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procedures can be accomplished with infusionbefore drawing off the decoction mash, withinfusion after drawing off the decoction mash,or as kettle-mash procedure (boiling of the to-tal mash, cooling, and saccharification with anenzyme extract that was drawn off at the begin-ning from the top liquid layer). When the maltis overmodified and enzyme-rich, then a high-temperature two-mash method can be used toadvantage. The infusion methods require goodmalt modification. Infusion-mash methods withdecreasing temperature have become popularfor extremely modified malts and certain beertypes such as ale. Mashing-in at 75 ◦C enhancesthe activity of α-amylase. During mashing-inthe temperature drops to 65 ◦C. Grist mash-ing methods are intended to treat the differentgrist fractions on the dual basis of their enzymecontent and their convertibility. In the processinvolving husk separation, the boiling of thehusks, and therefore their extensive leaching, isavoided.

Figure 8. Three-mash method—- Temperature of decoction mash- - - - Temperature of rest mash

Processing of Adjuncts. Unmalted cerealsmust be treated thermally before enzymaticbreakdown takes place, thus ensuring the con-version of extract-forming components. Maltamylases facilitate the gelatinization of thefinely ground adjuncts at low temperature. Thegrinding of the malt grist must correspond infineness to the grist part of the adjuncts, and theconcentration of themaltmashmust be kept very

high because a large amount of water is requiredfor optimum adjunct gelatinization (1 : 4 – 5).Corn is easier to process than rice, because it

gelatinizes at lower temperature. Up to 15 % ofadjunct can be added to the first decoction mashwithout any special treatment. If higher propor-tions of corn are added, a special adjunct mashwill be required, in which the ratio of corn tomalt is 2 : 1. When almost complete gelatiniza-tion and liquefaction have been achieved, theadjunct is boiled and subsequently added to themalt mash.

Some varieties of rice will gelatinize com-pletely only at 88 – 90 ◦C, even if malt is added.After gelatinization, sufficient malt mash held attemperatures of 30 – 40 ◦C is added; liquefactionthen takes place within 10 min at 78 ◦C. The liq-uefiedmaterial is subsequently boiled and addedto the actual malt mash. After that, the mashingprocedures described above can take place. Theprocessing of 10 – 15 % unmalted barley will bepossible only if the brewing malts are rich inenzymes. Higher proportions of unmalted bar-ley (30 – 40 %) require the addition of enzymeproducts.

3.2.3. Separation of Wort

After mashing wort is obtained in two steps: (1)lautering of the first wort by filtration, (2) leach-ing of the extract that remains in the spent grainswith hot water (sparging).

Lauter Tun. Commonly used lauter tunshave a total capacity of 8 hL/100 kg and spentgrain depths of 30 – 65 cm. They have a perfo-rated false bottom with an open surface repre-senting about 6 – 30 % of the plate area. Rotat-ing, height-adjustable raking machines loosenup the spent grain bed and a spray device deliversthe sparging water. During lautering aeration ofthe wort should be avoided. Themash should re-main homogeneous during pumping in, so that aloose, even filter cake can form. Finally, the wortthat runs off should be as clear as possible, sothat no particles which could disintegrate furtherduringwort boiling (filterability), and only smallamounts of the long-chain fatty acids, which de-stroy foam, can get into the kettle.

Because of the danger of washing out iodine-reactiveα-glucans, the spargewater should have

24 Beer

a maximum temperature of 78 ◦C. In order toavoid channelling, it should be delivered evenly.The ideal performance of a lautering process ina modern lauter tun is shown in Figure 9.

Mash Filter. In place of the lauter tun, sev-eral brewers employ mash filters to separate themash into solids and liquid. The total mash istransferred into a vertically arranged filter press.The frames are covered on both sides with filtercloth made of synthetic material. At the sametime, the air must escape quickly when the ho-mogeneous mash is pumped into the chambers.After yielding the first wort, water is pumpedin and the filter compartments of the filter pressare pressed togetherwith corrugated steel plates.Because very low volumes of sparging water(0.5 hL/100 kg) are necessary, this facility isvery suitable for high-gravity brewing.

Characteristic differences between well-automated mash filters and lauter tuns are thefollowing: (1) independence from the qualityof the malt and from the proportion of adjunct,(2) quicker lautering of the more highly concen-trated first wort, (3) higher yields, and (4)mostlya hazier filtrate.

Figure 9. Idealized lautering diagram using a lauter tun- - - - - - Extract concentration, wt%–·–·–·– Pressure under false bottom, mm– – – – Volume of wort, hL–�–�– Position raking mashine, mm

Strainmaster. The strainmaster consists of arectangular vessel, the bottom half of which isconically shaped. In the lower part of the vesselperforated sieve pipes of triangular cross sec-tion, which have an open surface area of 10 %,are arranged on top of each other. After pump-ing off the first wort the sparging water can bepumped in from the top and/or the bottom. A

very high first wort concentration of 20 – 23 %is necessary in order to achieve a homogeneousmash. Even with large amounts of sparging wa-ter it is not possible to achieve yields as high asthose obtained with the lautering systems pre-viously discussed, primarily because the spentgrains must be withdrawn while very wet. Themajor advantages of the strainmaster are its largecapacity and rapidity in action – lautering is fin-ished in 70 – 80min – and its simple, automaticoperation.

Continuous Lautering. Equipment that al-lows continuouswort lautering has not been suc-cessfully introduced into breweries because thewort that runs off is very hazy. The most im-portant features of such equipment include a ro-tary mash filter, a screen-conveyor centrifuge, abelt filter, a vacuum drum filter, the Pablo sys-tem with screen centrifuges and separators, andhydrocyclones.

Spent Grain Removal. Spent grain with amoisture content of 75 – 80 % is usually soldto farmers and provides a protein-rich nutrientfeed for cattle. Spent grains obtained from astrainmaster must first be demoisturized in ascrew press. Spent grains obtained from mashfilters have a moisture content of only 60 %.An amount of 100 kg of barley malt yields120 – 130 kg wet spent grains, whereas wheatmalt yields 10 – 15 % less. The dry matter con-sists of 23 – 28%protein, 5 – 9.5%fat, 40 – 47%nitrogen-free extract materials, 16 – 21 % crudefiber, and 4 – 6 % minerals.

3.2.4. Wort Boiling and Hopping

The wort obtained by lautering (full kettle wort)is boiled; during this time hops are added. Theprocess has several functions, namely: (1) evap-oration of excessive water in order to achieve thedesired wort concentration (original extract), (2)destruction of enzymes, (3) sterilization of thewort, (4) coagulation of the proteins (the flakyprecipitate is called hot break or hot trub), and(5) dissolution and isomerization of the bittersubstances of the hops in the wort. In addition,undesirable aroma components are removed, re-ducing substances are formed, color increases,and the pH value falls slightly.

Beer 25

Wort Boiling. The kettles must have a ca-pacity of 9 hL per 100 kg of malt grist in or-der to achieve the desired effect through boiling.The most important part of the kettle is its heat-ing mechanism. At first, direct firing was used;this was later changed to oil-heating, and thento steam-jacketed kettles with two-zone heatingand a cone-shaped central core.

Today hot water or saturated steam systems(internal or external heating) are frequently used.In conventional kettles the evaporation rate, rela-tive to the final volume, is 8 – 10% per hour. Fortechnological reasons, the boiling time shouldnot be less than 90min. The denaturation andsubsequent coagulation of proteins will leadto coarse, flaky precipitation products (break)and nonopalescent worts only if the finely di-vided protein complexes have sufficient chanceto come into contact with each other for ag-glutinization; this is achieved by using smallsteam bubbles and boiling movement. Boilingby means of various external heating systemsprovides proper rolling and control of the wort;it results in a high evaporation rate of 10 – 15 %per hour as well as a quick and extensive sep-aration of coagulable nitrogen, so that the boil-ing time can be shortened to 75min. Further de-crease of the boiling time is not possible becauseof the length of time required for the isomeriza-tion of the bitter substances. However, heatingat 108 – 112 ◦C enables the boiling time to befurther reduced to about 60min.Continuous Wort Boiling. Completely new

possibilities are offered by continuous high-temperature wort boiling systems. At a max-imum temperature of 135 ◦C, the hot holdingtime required is claimed to be only 150 – 160 s.At higher temperature, heterocyclic nitrogencompounds will increasingly form; these havea very low flavor threshold, and impart a bread-like or cracker-type aroma to beer [30]. Afterthe hot holding period, evaporation proceeds intandem flash evaporators, and should amount toat least 6 % of the original volume in order todrive off such undesirable aromatic substancesas aldehydes, ketones, hydrogen sulfide, anddimethyl sulfide. When these parameters arecarefully observed, beers can be produced withhigh-temperature wort boiling which are of thesame quality as those produced under normalboiling conditions [38].

Hopping. The dissolution of the bitter sub-stances is very dependent on pH. At a pH of 5.9,the α-acids are molecularly dispersed, partly assalts (humulates); their solubility is 480mg/L.However, at a pH of 5.2 only 84mg/L can bedissolved in a colloidal state. At the normal wortpH of 5.4 – 5.6, the colloidal solution prevails.During wort boiling, up to 40 – 60 % of humu-lone, cohumulone, and adhumulone isomerize;5 – 1 % remain unisomerized. A proportion ofthe bitter substances is oxidized, which also con-tributes to the bitterness of the beer. The majorpart of the loss must be attributed to incompleteextraction from the hop cone or hop products,and to precipitation. The remaining α-acids arerendered insoluble as a result of the fall in pHduring fermentation, and are expelled in the fer-mentation cover. The β-acids are not transferredto the wort, but the soft and hard resins are dis-solved during boiling, and also impart a certainbitter taste.

The isohumulones aremore soluble at lowpHvalues, e.g., about 2000mg/L at pH 5. Boilingand hot stand times are essential for isomeriza-tion. In addition, extraction speed, the age of thehops, the amount of α-acids added, and the wortpH all affect isomerization. If additional contactsurfaces are available (as in hop extract pow-ders), the isomerization will occur faster. Sepa-rate addition of tannin extracts at the beginningof boiling and of extracts of bitter substanceslater will result in a higher bitter substance yield,because the bitter substances otherwise adsorbonto the hot trub particles and are lost. In thebrewhouse, about 60 % of the bitter substancescan be transferred to the wort; only 30 % of theamount originally added remains in the finishedbeer because of further precipitation during fer-mentation.

The amount of bitter substance added is ex-pressed in mg α-acid per liter of finished wort,and varies according to the hop product used,and the beer type and variety. Pale beer containsabout 65mg/L, export 80mg/L, and pilsener80 – 160mg/L.

The addition of hops according to variety andtiming also influences the bitterness of the beer,but most of all the yield of aroma substances.

Color. Coloring and reducing substances areformed during kilning and mashing. Others de-velop during boiling of the wort. The numer-

26 Beer

ous amino acids react with reducing sugars toform intermediary products which undergo fur-ther transformation to brown melanoidines. Theproducts thus formed possess reducing proper-ties and give acid reactions. Polyphenols alsoadd to the color formation by nonenzymatic ox-idation and polymerization. Strong formation ofcoloring compounds leads to broad and harshtasting beers which age quickly.

The Finished Wort. The hopped beer wortobtained after boiling is designated as finishedwort (cast wort, hot wort). Its extract contentand volume needs to be analyzed. The brew-house yield can be determined from these val-ues; the extract yield is expressed as a percentageof the amount of malt used (range between 78and 81 %). Table 6 shows the composition of apale 12 % finished wort.

Table 6. The composition of pale lager wort (12 %) made frombarley malt

Carbohydrates (100 %):Hexoses 7 – 9 %Sucrose 3 %Maltose 43 – 47 %Maltotriose 11 – 13 %Lower dextrins 6 – 12 %Higher dextrins 19 – 24 %Pentosans 3 – 4 %Gums 0.2 %

Nitrogen compounds:Total nitrogen 950 – 1150mg/LHigh molecular mass nitrogen 200 – 300mg/LLow molecular mass nitrogen 550 – 700mg/LFree amino nitrogen 200 – 250mg/L

Bitter substances 25 – 35 EBCbitter units

Polyphenols:Total polyphenols 180 – 250mg/LAnthocyanidines 70 – 110mg/L

Minerals 15 – 20mg/L(80 % inorganic,20 % organic)

Zinc 0.1 – 0.25mg/LpH 5.0 – 5.7Viscosity (20 ◦C) 1.7 – 2.0mPa · s

Wort Concentrates. In some countries it ispermitted to manufacture hopped wort concen-trates and unhopped malt extracts from wortmade by the usual brewing method. Concentra-tion to 70 – 80% drymatter is achieved either byvacuum evaporation or by lyophilization. Theseconcentrates can be diluted back to the desiredextract content in the kettle; they are processedsubsequently in the normal manner.

3.2.5. Wort Treatment

Hot Trub Separation. The hot trub containsthe nitrogen compounds that coagulate duringboiling. These must be removed completely be-fore fermentation, or else the beer will tastewort-like, bitter, and even harsh. The hot trubconsists of 40 – 70%protein, 7 – 15%bitter sub-stances, 20 – 30 % of other organic compounds,such as polyphenols, and mineral substances.Hot trub yield is between 400 and 800mg ofextract-free dry matter per liter of finished wort.When whole hops are used, the cast wort mustfirst be cleared of spent hops by passing itthrough a hop back. In the past, the wort waspumped into the flat coolship, where it wouldcool, and the hot trub and part of the cold trubwould sediment. Because of the danger of infec-tion on the large surface of the coolship, the heatloss, and the great expenditure of work, othermethods of hot trub separation have been devel-oped.

The settling tank (hot wort receiver) permitsa good separation of the trub and spent hops, butthe amount of sludge collecting on the bottomof the vessel creates problems because 2 – 5 %of the wort is trapped in this sludge. It can, how-ever, be recovered by centrifuging themixture oftrub, spent hops, and wort employing a chamberor plate centrifuge. The wort recovered in thisway can be added to the same batch of wort orto the next brew.

The total hot wort is frequently clarified bymeans of efficient, self-cleaning centrifuges;these, however, will only work reliably if thewort – trub mixture is added homogeneously.This can usually be achieved by means of anintermediate hot wort tank with a stirring mech-anism. The most thorough removal of trub andspent hops can be achieved by filtering the hotwort through kieselguhr.

An inexpensive solution is the whirlpooltank, where the wort is pumped tangentially intoa cylindrical vessel. This creates an even, rotat-ing stream. The solid particles suspended in therotating liquid will separate due to friction (teacup effect), migrate to the bottom center, andcoalesce to form a cake. It is also possible toachieve this effect in whirlpool kettles, whereboth boiling and trub separation take place, pro-vided that the bottom of the kettle is appropri-ately shaped.

Beer 27

Wort Cooling. The wort, which has beenfreed of hot trub, is cooled to 4 – 7 ◦C for coldbottom fermentation, to 10 – 15 ◦C for acceler-ated bottom fermentation, and to 12 – 18 ◦C fortop fermentation.

Cold Trub Removal. The very fine flakedcold trub appears at temperatures of 70 – 55 ◦C.It consists of around 50 % protein, combinedwith 15 – 25 % polyphenols and 20 – 30 % car-bohydrates of high molecular mass. At 0 ◦Cabout 150 – 300mg/L of cold trub is formed.Opinions are divided regarding the necessity ofcold trub separation. The presence of cold trubcan, under certain circumstances, accelerate fer-mentation because of the presence of long-chainunsaturated fatty acids. The yeast will contain ahigher level of impurities and the filterability ofbeer brewed in this manner may be poor.

A fairly good separation of the cold trub canbe obtained in the starting vessel by sedimen-tation after pitching. Even more effective are:cold sedimentation with or without the additionof kieselguhr, cold centrifugation, and, very ele-gantly, flotation not only with aeration but the si-multaneous addition of pitching yeast. Filtrationof the wort removes the cold trub quantitatively;however, a deficiency ofminerals and fatty acidscould be created by thismethod. Blending of un-filtered wort can be helpful in this case.

Aeration. The oxygen necessary for yeastpropagation (7 – 8mg/L, corresponding to 80 %saturation of the wort with O2) is usually intro-duced in the form of air at the pitching temper-ature. If pure oxygen is used, it must be addedcarefully, so that the oxygen level does not ex-ceed 15mg/L; a higher level is detrimental to theyeast. Optimum aeration can compensate for thedisadvantages of an extensive wort clarification.All closed cooling systems require separate aer-ation of the wort. During normal wort aeration5 – 15 L of air per hectoliter of wort is needed;flotation requires 40 – 60 L/hL.

Sterile air may be introduced on the coldwortside of the plate cooler with even dispersion byair nozzles or venturi jets, or in the hot wort cen-trifuge, provided thewort is cooled immediately.A combined hot and cold aeration in the ratio of1 : 5 also is possible.

3.3. Bottom Fermentation

The flow sheet of Figure 10 describes the basicoperations for popular beer varieties from fer-mentation to finished beer.

Figure 10. Flowsheet of beer fermentation from pitchingto final productSubstances that are shown in dotted ellipses are not neces-sary

28 Beer

3.3.1. Fermentation

The fermentation process is initiated by the addi-tion of 0.5 – 0.7 L of a heavy yeast slurry per hec-toliter of wort, corresponding to 15 – 20× 106

yeast cells per milliliter of cooled and aeratedwort. This procedure is called pitching. Thebatchwise addition of original wort to ferment-ing greenbeer is calleddoubling. Themain prod-ucts resulting from the fermentation are etha-nol and carbon dioxide. Other reaction prod-ucts include: higher aliphatic and aromatic alco-hols, esters, organic acids, carbonyl compounds,sulfur-containing compounds, and polyhydricalcohols, all of which are important for the prop-erties and quality of the resulting beer (for detailson alcoholic fermentation, see →Ethanol). Allthe compounds formed have different taste andodor thresholds. Their combined contributionsmake up the flavor or off-flavor of the beer; theamounts produced can be influenced to some de-gree by brewing technology. Further changes inthe wort are caused by the fall in the pH value(see below). The pH drop leads to the precipi-tation of nitrogen compounds of high molecularmass, of polyphenols, and of bitter agents. Theresult is a decrease in color and a debitteringeffect.

Yeast has the ability to adjust its metabolismto aerobic aswell as to anaerobic conditions. Theyeast doubles or triples its mass during fermen-tation. For the build-up of cell substance (pro-teins and enzymes) the yeast needsmostly aminoacids,which it either takes from the fermentationsubstrate or must synthesize by itself. Besidesproteins, lipids are also synthesized for yeastpropagation because they are important compo-nents of the cell wall, and are needed for the up-take of nutrients. For the synthesis of these lipidsfrom acetyl coenzyme A, molecular oxygen isneeded; after lautering, wort itself contains onlyfew lipids. Finally, the yeast also requires min-erals for the stabilization of its enzyme systems.

Fermentation Byproducts. During themain fermentation, the pH value decreases byone unit because volatile (acetic, formic) andnonvolatile organic acids (pyruvic, malic, cit-ric, lactic) are formed. The pH of beer rangesfrom 4.3 – 4.6. The intensity and speed of acidformation is determined by the buffering actionof the wort, the amount of easily assimilated

nitrogen, the yeast strain, and the fermentationschedule used. If the pH drops quickly, gumsthat retard filtration will precipitate, but valu-able colloids also are lost. The pH has a directeffect on the flavor and the liveliness (sparkle)of the beer. Short-chain fatty acids are formedduring the fatty acid synthesis at the beginningof the main fermentation process: butyric, iso-valeric, hexanoic, octanoic, and decanoic acid.Their amounts can be controlled by the wortcomposition, aeration, yeast strain, and generalfermentation conditions. During pressure fer-mentation, increased levels of these compoundscan be expected during maturation. Even in verylow concentrations, they cause a yeasty odor andimpair head retention.

The higher aliphatic alcohols (1-propanol, 2-methyl-1-propanol, 2-methyl-1-butanol, and 3-methyl-1-butanol) and aromatic alcohols (espe-cially 2-phenyl-1-ethanol) represent the largestfraction of the compounds responsible for thearoma of the beer; at concentrations which aretoo high, they will adversely affect taste andquality. Their levels can be controlled to someextent by manipulating the content of free ami-no nitrogen, wort concentration, pitching rate,yeast strain, pitching temperature, and fermen-tation temperature.

Because of their low taste threshold values,esters strongly influence the organoleptic prop-erties of the beer. Esters are products of en-zymatic catalysis and their formation is veryclosely related to yeast propagation and lipidmetabolism. Wort aeration, pitching rate, fer-mentation temperature, the yeast strain, and thecounterpressure during fermentation all havegreat influence on ester formation. Measures in-tended to intensify yeast propagation will lowerester concentration.Sulfur compounds (hydrogen sulfide, sul-

fur dioxide, dimethyl sulfide, 3-methylthio-1-propanol, and thiols) are not desirable in beerbecause of their specific odor and taste. Besidesefficient trub removal the most important factorin the formation and reduction of these flavor-active substances is the yeast strain.Glycerol (1300 – 2000mg/L) is formed as a

byproduct during glycolysis; its concentrationdepends on the amount of fermented sugars.Aldehydes and ketones are responsible for

the aroma of green beer and for the stale fla-vor. Acetaldehyde formed in the green beer does

Beer 29

not present any technological difficulties. Off-flavors in beer are usually caused by a high levelof diacetyl and 2,3-pentanedione; these com-pounds are responsible for unfavorable, butteryflavor in the beer. The taste threshold of di-acetyl depends on beer type, and ranges from0.10 to 0.12mg/L; that of 2,3-pentanedione is0.5 – 0.6mg/L.

3.3.2. Maturation

The total diacetyl concentration is used to judgethe maturity of purged beer, and must be de-creased below the flavor threshold by means ofbrewing technology. The diacetyl precursor 2-acetolactate is called “potential diacetyl”, be-cause it transforms into free diacetyl only in thefiltered, yeast-free beer, and can then not be bro-ken down any further. In calculating the totaldiacetyl concentration, 2-acetolactate must beadded to the amount of free diacetyl.Diacetyl Metabolism. During the propaga-

tion phase the yeast cells need numerous ni-trogen compounds for the formation of yeastprotein. If there is not sufficient fixed nitro-gen present in the wort in the form of com-pounds which can be assimilated, the yeast willuse a combination of carbohydrate and proteinmetabolism.During the valine synthesis diacetylcan be formed via 2-acetolactate by oxidativedecarboxylation as shown in Figure 11. Thisstep, which is catalyzed by yeast enzymes, ishighly temperature-dependent, and occurs veryslowly below 10 ◦C. Diacetyl itself is presentin very small quantities in fermentation samplesand in green beer, because its reduction to ace-toin is much faster than its formation. The fi-nal product 2,3-butanediol is, as far as taste isconcerned, unobjectionable; its concentration inbeer never exceeds its flavor threshold. Bacteria,which may occur in the brewery as infections,also are likely to promote the formation of di-acetyl by the route shown in Figure 11. Sometypes of bacteria contain an enzyme which candecarboxylate 2-acetolactate directly to acetoinwhile avoiding the limiting maturation step.

Fermentation Conditions. The formationand reduction of 1,2-diketones is dependent on(1) a sufficient supply of free amino nitrogenand other yeast nutrients, (2) proper pitching

and doubling conditions (sufficient aeration, lowpitching temperature, optimization of pitchingrate regarding yeast quantity and timing), (3) acareful selection of the yeast (yeast strain, phys-iological condition of the yeast, no infection),and (4) control of the fermentation and matu-ration conditions favorable for the degradationof diacetyl. The most effective parameter in thisrespect is temperature control during fermenta-tion and maturation, which is the basis for thefermentation procedure shown in Figure 12.

Using the combination of cold fermentation –cold maturation, a tasty beer can be produced bysimplemeans. It is advantageous to removemostof the yeast at the end of fermentation and toachieve secondary fermentation by the additionof “krausen” (green beer in its initial fermentingstage).

If the combination of warm fermentation –warm maturation is considered, the formationof fermentation byproducts is increased at theprevailing high fermentation temperatures. Therapid pH drop results in losses of bitter sub-stances, decreased foam stability, and an unsatis-factory yeasty flavor. Pressure fermentation us-ing carbon dioxide is a remedy. Thiswill slightlydecrease the fermentation rate and control yeastpropagation, thus curbing the formation of fer-mentation byproducts.

The combination cold fermentation – warmmaturation avoids the formation of undesirableflavors and decreases the level of diacetyl safely;it leads to beer of constant quality. In this case,temperature control is optimally adjusted to themetabolism of the yeast. In programmed matu-ration, heat exchangers are used in order to raisethe temperature to 20 ◦C. The addition of 10 %“krausen” with an apparent degree of attenua-tion of 20 – 30 % is practiced at the beginning ofthis maturation phase. Accelerated fermentationand maturation are also achieved by stirring fer-mentations and then maintaining a maturationstep and subsequently purging green beer withcarbon dioxide. However, an excess of fermen-tation byproducts is formed by this method.

Fermenters. Fermentation and maturationare carried out in open or closed fermenters, hor-izontal tanks, or vertical fermentation tanks withconical bottoms [39]. In two-tank processes, fer-mentation, maturation, and storage occur sepa-

30 Beer

Figure 11. Synthesis of diacetyl by yeast and bacteria

Figure 12. Fermentation in practiceA) Cold fermentation – cold maturation. B) Warm fermentation – warm maturation. C) Cold fermentation – warm maturation

Beer 31

rately; vertical tanks with conical bottoms areused in this case.

The capacity of the cooling equipment andheat exchange surface of the tanks should be de-signed for maximum heat development or, in thecase of single-tank processes, for a maximumcooling rate.

Fermentation Stages. The brewer identifiesthe changes occurring in the green beer bycarefully observing the individual fermentationstages: the creaming, the head formation, therocky head, and the decreasing of head at theend of fermentation. Extract decrease and tem-perature level must be checked constantly. At-tenuation also is indicated by a fall in pH value,by a phase of cell propagation and cell sedimen-tation (turbidity), by a decrease in coloration,and by a lowering in redox potential.

The carbon dioxide formed during fermenta-tion amounts to 2 – 2.5 kg per hectoliter of beer.It is collected and can be used for carbonation ofsoft drinks or for low-oxygen bottling and rack-ing.

3.3.3. Cold Storage

During cold storage the beer must be carbon-ated to the desired CO2 level (0.48 % for draftbeer, 0.50 % for canned beer, 0.55 % for bottledbeer). This can be achieved in the conventionalprocedure by using a definite bunging overpres-sure of 0.2 – 0.6 bar, depending on hydrostaticpressure and temperature. Beers that underwentwarm maturation require either higher pressure,or carbon dioxide to be added during transferfrom warm to cold storage tanks. During stor-age, the beer must clarify by allowing the yeastand other haze-causing materials to settle, andits taste must refine and round off. In order toachieve these requirements, the beer must bestored at 0 to− 2 ◦C during the last week or two.When warm maturation is practiced, the storageperiod cannot be as easily defined. Frequentlyfermentation, maturation, and storage take placein the same vessel (one-tank process).

By using separate tanks for the sedimenta-tion of the yeast after fermentation (flocculationtanks), yeast content and degree of attenuationare further balanced. During transfer to the coldstorage tanks krausen is added. Separate storage

tanks also are used when the beer is stabilizedwith bentonite during the second half of the stor-age period.

Continuous fermentation may be accom-plished by through-flowor by tributary-flow sys-tems or in a bioreactor. Thesemethods are rarelyfound in large production facilities.

3.3.4. Filtration

For filtration theory and beer filtration, see [40].Besides an impeccable taste, perfect clarity

is expected of a stored and matured beer. Solidand hazy particles still present in the beer (yeast,protein – tannin particles, and hop resins) are re-moved by filtration. Filtration also improves bi-ological and chemical-physical stability. Filtra-tion is carried out at low temperature (possiblyat 0 to − 2 ◦C) under a counterpressure of car-bon dioxide above its saturation level, and withminimum uptake of oxygen [42].

Filtration systems used for pre-clarificationwere formerly pulp filters; today brewers usemostly plate and frame filters, pressure leaf fil-ters, or candle filters for cake filtration with a fil-ter aid (diatomaceous earth [41], perlite), or cen-trifuges. For subsequent final clarification andsterile filtration, sheet filters made from cellu-lose and diatomaceous earth are used. For sterilefiltration filter membranes made from celluloseesters of definite pore size may be used.

The choice of the clarification method de-pends on capacity, technical considerations, andeconomic conditions. Another factor is the filter-ability of the beer, which is not always propor-tional to the viscosity, but also depends upon thenature and amount of filtration-retardant materi-als present, such as α- and β-glucans, proteins,and a high yeast content.

3.3.5. Stabilization

In bright beer high molecular proteins and tan-nins tend to aggregate and form haze. This pro-cess can be delayed by removing one of thesefractions which improves the chemical-physicalshelf life of the product. Most common is theremoval of part of the tannins by adding poly-vinylyrrolidone (10 – 50 g/hL) as an adsorbent.Polyvinylpyrrolidone is dosed in the filtered

32 Beer

beer and retained in a pressure leaf filter. Theloaded polyvinylpyrrolidone is subsequently re-processed and reused.

3.3.6. Types of Bottom-Fermented Beers

In many countries, bottom-fermented beer isdesignated as lager beer [43]. Its extract of orig-inal wort varies according to local laws (tax clas-sification) from 7 to 14 %. Lager beers are themost popular, with an average bitter substancecontent of 20 EBC bitter units (see Table 7 andSection 5.3).

Table 7.The composition of bottom-fermented pale lager beer (12%extract of original wort)

Extract of original wort 12.0wt % (125.6 g/L)Attenuation limit (apparent) 78 – 85 %Real degree of attenuation 65 – 80 %Apparent residual extract 1.7 – 3.0wt %Real residual extract 2.0 – 3.5wt %Alcohol concentration 3.5 – 4.5wt %Total nitrogen 700 – 900mg/LCoagulable nitrogen 8 – 28mg/LHigh molecular mass nitrogen 150 – 250mg/LLow molecular mass nitrogen 300 – 600mg/LFree amino nitrogen 80 – 160mg/LBitter substances 16 – 25 EBC bitter unitsTotal polyphenols 130 – 180mg/LAnthocyanidines 40 – 80mg/LpH 4.3 – 4.6Viscosity (20 ◦C) 1.4 – 1.7mPa · s

Beer with an Extract of Original Wort of10 – 14 %. This range comprises an extraordi-narily large variety of beer types, including paleand dark beers, export beers (more than 12 %extract of original wort), Marzen beers, specialbeers, and festival beers (13 – 14 % extract oforiginal wort). Within these limits there are suchdifferent beer types as Pilsener, Dortmunder,Munich, as well as smoky-flavor beers and cel-lar beers; these are however restricted to cer-tain localities. The upper gravity limits for spe-cial beers differ from country to country: for in-stance, In Germany 14 %, in Austria 13 %, inItaly 14 %, and in France 15 %.Strong Beer. In Italy, pale and dark beers of

more than 15% extract of original wort are clas-sified as strong beers; in Austria and Germanybeers from 16 % up to a maximum of 28 % ex-tract of original wort also belong to this class.

3.4. Top Fermentation

Top-fermented beers differ from bottom-fermented beers by their special aroma whichis primarily induced by the top-fermenting yeaststrains of Saccharomyces cerevisiae. The partic-ular yeast strain employed has a higher optimumfermentation temperature, and therefore the fer-mentation proceeds between 12 and 25 ◦C. Dur-ing fermentation, the yeast rises and can beskimmed off the top. In large vessels, espe-cially the cylindrical fermentation tanks withconical bottoms, the yeast is, however, croppedin the same manner as in bottom fermentation.The number of yeast generations is consider-ably greater. At the higher fermentation temper-ature, the amount of diacetyl is usually easilydecreased. Because of the fast rate at which fer-mentation proceeds, a relatively low pH value of4.1 – 4.3 results.

Types and Production of Top-FermentedBeers.Wheat Beer [44]. The extract of original wort

in wheat beer is 11 – 14 %; the wheat malt por-tion can range from at least 50 to 100 %. An in-tensive two-mash decoction procedure is neededin the brewhouse in order to ensure a satisfac-tory proteinmodification, because an increase inwheatmalt proportionally decreases the concen-tration of assimilable nitrogen compounds in thewort. Because of the higher pitching temperature(12 – 18 ◦C), the pitching rate required will belower (0.3 – 0.5 L of yeast per hectoliter of orig-inal wort, corresponding to 7 – 15× 106 yeastcells per mL). The aeration should ensure anoxygen concentration of 6 – 8mg/L. The initialfermentation stage is characterized by the riseof trub particles and hop resins to the surface.After their removal, yeast rises to the top andcan be cropped; this continues until the end offermentation. The special wheat beer yeast canbe repitched as often as 200 – 500 times. Wheatbeer is characterized by a typical spectrum offermentation byproducts, such as 4-vinylphenoland 4-vinylguaiacol; these two compounds areresponsible for the typical aroma of wheat beer.A more rapid and extensive pH drop, an in-creased formation of higher alcohols and esters,together with a greater decrease in nitrogen andbitter compounds,mark the course ofwheat beer

Beer 33

fermentation as comparedwith lager beer proce-dures. A higher bunging pressure during storageensures a carbon dioxide concentration in wheatbeer of 0.7 – 0.9 %. If wheat beer is marketedas “naturally hazy”, the secondary fermentationcan be accomplished in the bottle by adding un-fermented wort and bottom-fermenting yeast orbottom-fermented krausen. Crystal-clear wheatbeer remains in the tank until mature and is sub-sequently filtered and bottled.Alt beer also has an extract of original wort

of 11 – 14 %. Methods vary widely for the pro-duction of the dark Alt beer which gives read-ings of 25 – 40 EBC coloring units: the wortmay be produced from pale malt with the addi-tion of caramel coloring or colored beer, 100 %dark malt, or 90 % pale malt and 10 % darkcaramel malt. A proportion of 10 – 15 % palewheat malt sometimes is used to round off thetaste. The black malt which is used as a sub-stitute for caramel may also be produced fromwheat. The bitter substance concentration of Altbeer amounts to 28 – 40 EBC bitter units. Thefermentation temperature is 12 – 22 ◦C.Kolsch beer (extract of original wort

11 – 14 %) may be produced only in the townof Cologne. It is brewed with pale barley maltby adding up to 10 – 20 % wheat malt, andfermented at 12 – 22 ◦C, but sometimes up to28 ◦C. The character of Kolsch and Alt, for-merly designated as top-fermented bitter beers,is strongly determined by the properties of thespecific yeasts; a large variety of flavors results.Berliner Weisse (White) also is named after

its place of origin; it has an extract of origi-nal wort of 7 – 8 %. Its very low pH value of3.2 – 3.4 originates from the combined yeast andlactic acid fermentation. A degree of attenuationsometimes exceeding 100%results in an alcoholconcentration of 2.5 – 3 % and a lactic acid con-centration of 0.25 – 0.8 %. The bitter substancecontent amounts to 4 – 6 EBC units, whereas thecarbon dioxide concentration lies between 0.6and 0.8 %. The beer has an acidic taste, whichis marked by a pleasant estery – flowery quality,dependingon theproductionmethodand thepar-ticular type of beer; it is frequently served withraspberry or woodcruff syrup.Malt Beer. Sugar and sugar syrup may be

used in the production of top-fermented nutri-ent beers. The beers are brewed with 7 – 8 %extract of original wort, and are enriched after

filtration with sugar until an extract of originalwort of 12 % results. The alcohol concentrationof malt beer must be under 0.5 %. The pH liesbetween 4.5 and 4.9 depending upon the methodofwort production and the degree of attenuation;the carbon dioxide concentration is 0.4 – 0.5 %,the color rating ranges from 50 to 80 ECB units(65 – 80% dark malt, 3 – 5% dark caramel malt,3 – 5 % acid malt, and the remainder pale malt)and the bitter substance content is 6 – 10 EBCunits. Malt beers are pasteurized on account oftheir high content of fermentable sugar.British Ales. British ales have an extract of

original wort of 7 – 13 %, according to the taxcategory. Depending on the type of malt chargeand adjunct (mostly corn), on the choice of top-fermenting yeast strains, as well as on the “prim-ings” added in the cold storage tank (caramelcoloring), various types are obtained such as ale,brown ale, and bitter ale. The so-called “best bit-ter” is remarkably bitter due to special hoppingmethods; it also possesses a strong hop aroma.Bottled and canned beers are filtered, carbon-ated, and stabilized, according to the demandsof the market. The original draft ale is clarifiedwith gelatine or isinglass, and dry-hopped in thebarrel or keg.Stout is a dark, strongly hopped beer, with

an extract of original wort between 11 and18 %. The weaker stouts also are called porter.Some of these are treated with a specialpost-fermentation yeast (Saccharomyces bret-tanomyces), which imparts a typical aroma tothe product.Geuze and Lambic are Belgian sponta-

neously fermenting beerswith an extract of orig-inal wort of 11 – 12 % [45]. They are producedfrom certain admixtures of raw materials otherthan malt. The hop content varies widely, asdoes the method of wort production. Fermen-tation is not caused by a definite yeast strain, butby the airborne organisms of the fermentationrooms and vessels. Because of this spontaneousfermentation, the beers vary not only in theiralcohol level, but also in their lactic acid con-centration. According to the amount of acidity,the beers are either left in a natural state andconsumed with added sweeteners, or a specificamount of sweet mash is added.Top-fermented strong beers with an extract

of original wort of more than 16 % include the

34 Beer

German pale and darkWeizenbock beers as wellas the different varieties of stout.

3.5. Special Production Methods

A number of special production methods havebeen designed to produce beers with very spe-cific properties. The legal regulations coveringsuch products differ in various countries.

3.5.1. Dietetic Beer

Dietetic Beers are pale beers of Pilsener brewingtype; in Germany they may contain only 0.75 gbioavailable carbohydrates and 0.5 g protein per100 g of beer. In order to achieve these figures,wort of 11 – 12%extractmust be fermenteduntilthe apparent degree of attenuation is more than100 %. Brewhouse procedures are adapted to-wards achieving this aim by employingmashingwith extended rest periods at 60 – 66 ◦C. Duringcold fermentation (7 – 12 ◦C), a small propor-tion of malt extract that has been drawn from themash at 50 ◦C is added. This causes breakdownof the remaining high molecular mass carbohy-drates and proteins. The addition of malt flouralso has proved successful in obtaining the prop-erties of dietetic beer. The beer must be care-fully stabilized because the addition of unboiledextracts increases considerably the amount ofcoagulable nitrogen compounds. Almost com-plete breakdown and fermentation of the ex-tract results in the alcohol concentration risingto 4.8 – 5 %. This is partly viewed as a disad-vantage. Thus, the alcohol concentration is sub-sequently lowered by either distillation in filmevaporators or reverse osmosis. It is much easierto produce dietary beer with a lower extract oforiginal wort because the control of both alcoholconcentration and fermentation is simpler. Theintensive fermentation leads to pH values in therange of 4.1 – 4.5; the bitter substance contentvaries between 22 and 40 EBC units.

3.5.2. Nutrient Beer

Nutrient beers are bottom-fermented beerswhich are brewed with 100 % malt. They are

classified either as “low-alcohol” (alcohol con-centration under 1.5 %) or as “alcohol-free” (al-cohol concentration under 0.5 %). The extractof original wort of these very dark beers (60 – 80EBC coloring units) is between 11.5 and 12.7%;the apparent degree of attenuation is 25 – 30% inthe low-alcohol beer and 8 – 10% in the alcohol-free beer. The pH is 4.7 – 4.9, according to thedegree of attenuation and other technologicalsteps (acid malt); the bitter substance contentis low (6 – 10 EBC units). The flavor of alcohol-free nutrient beers may be improved by increas-ing the alcohol concentration to 0.7 % and thenblending with first-wort extract before filtration.It is also possible to remove the alcohol partly.Complete pasteurization of such beers ismanda-tory.

3.5.3. Low-Alcohol Beer and Alcohol-FreeBeer

The many varieties of low-alcohol beers may bedivided into three groups:

1) Beers where the fermentation is stopped byfiltration and pasteurization. An alternativeto heat treatment is a cold shock process,during which a beer that has just started toferment is rapidly cooled in a thin film. Thisproduces a spectrumof fermentationbyprod-ucts similar to that of normal beer.

2) Beers that are fermented with a special yeaststrain, e.g., Saccharomyces ludwigii; theseyeasts metabolize only hexoses and sucrose.The major fraction of the malt sugars, suchas maltose and maltotriose, remains unfer-mented.

3) Beers that are fermented almost normally,but where part of the alcohol is later with-drawn by thin-film evaporation, vacuum dis-tillation, reverse osmosis, or dialysis.

They latter two methods are currently the mostcommon ones, because the taste of the dealcol-ized beer is more similar to that of normal beer.

3.5.4. High-Gravity Brewing

This procedure is popular because existing in-stallations can be better utilized and because ahigher capacity can be achieved without new in-vestment [43]. In general, the wort is brewed

Beer 35

as strongly as the brewhouse equipment willpermit, e.g., with 13 – 18 % extract of origi-nal wort instead of 11 – 12 %. Concentrationsof 16 – 18 % are only attainable without loss ofyield if syrups are added at the end of wort boil-ing. After fermentation and maturation, thesestronger beers are adjusted to the desired extractof original wort with carefully processed wa-ter (deaerated, carbonated, and sterilized). Thewort concentrations are usually no higher than14 – 1 5% so as to maintain the ratio and level ofbyproducts and, thereby, the normal beer taste.High-gravity beers always have a poor head re-tention.

3.6. Filling

After filtration, all operationsmust be directed tomaintain the quality of the beer. Mistakes madeat this point are very hard to rectify and willonly become noticeable much later (re-infectionand aged taste caused by a high oxygen concen-tration). Furthermore, the beer must be bottledunder an appropriate pressure to prevent the es-cape of carbon dioxide. Filling and packagingare subject to various legal regulations just asthe production of beer itself. These regulationspertain to labeling, container capacity, and vol-ume tolerance.

The amount of beer lost depends on the pro-duction facilities, and to a certain extent on ca-pacity, and ranges between 3 and 10 %. Exami-nation of beer loss provides an insight into lossof volume, which occurs from casting to the ac-tual process of bottling, and into loss of extract.

Kegging. Barrels are manufactured of oakwood, aluminum alloys, stainless steel, or syn-thetic materials lined with stainless steel; theirsize ranges from 10 to 250 L. After the barrelhas been thoroughly cleaned, it is purged withcarbon dioxide or, less advantageously, with air,and filled under counterpressure (isobaromet-ric). Bowless filling units not only avoid the dan-ger of infection, but they also protect the beerfrom extensive contamination with oxygen.

Barrels with a cylindrical edge are calledkegs or system barrels; they have a permanentlyinstalled fitting for cleaning, sterilization, fill-ing, and tapping. With such a device, the bar-rel remains sealed and under a pressure of car-

bon dioxide even after it has been emptied. Inthis fashion the drying-up of beer remnants isavoided, and cleaning is facilitated. Cleaningand filling under sterile conditions are easily au-tomated. Kegs and fittings are standardized.

Cellar Tanks. For larger distributors station-ary draft beer tanks which hold 10 to 30 hL canbe installed. The beer is delivered from the brew-ery in large tank trucks. The cellar tanks areequipped with cooling devices. They are linedwith disposable polyethylene bags,whichmakesit possible to store the beer under impeccablesanitary conditions without the need to cleanthe cellar tank. The excess pressure necessaryto dispense the beer is created by gas which isadmitted between the inner wall of the tank andthe polyethylene bag.

Bottling. Bottles may be made of glassor plastics [poly(ethylene terephthalate), PET,or poly(ethylene naphthalate, PEN)]. Whereasglass is diffusion-proof, not only can carbondioxide escape fromplastic bottles, but also oxy-gen can diffuse into the beverage, and cause anundesirable oxidation taste. A metal crown withsynthetic liner is widely preferred over othermeans of sealing the bottles. Returnable bottlesmust be cleaned to a microbiologically impec-cable standard before refilling. The step can bepreceded by a steam treatment. Disposable bot-tles are relatively expensive because their man-ufacture requires more energy and raw materialthan multiple-use bottles.

Isobarometric bottling of glass bottles is bestcarried out by pre-evacuation of the bottles, in-termediate puging with carbon dioxide, secondevacuation, counterpressurizing and then fill-ing. After filling fobbing is induced by vari-ous means; this provides for a maximum dis-placement of air. The crown closure machinepresses the crimped edges of the crown aroundthemouth of the bottle, which is then labeled au-tomatically. Modern bottling machines fill up to120000 bottles per hour. Brown glass bottles arepreferred to those made of green glass, becausebrown bottles protect the beer better against lightof short wavelengths, which causes photodegra-dation of the bitter acids of hops, and hence givesrise to a “light stroke”.

36 Beer

Canning. Cylindrical cans of aluminum ortinplate are closed with a flat lid equipped witha ring pull-tab.Anonporous synthetic resin coat-ing is applied to the inside of the can so as to pre-vent a chemical reaction occurring between themetal and the liquid. Pre-evacuation is only pos-sible with stable tinplate cans. Otherwise cansare purged with an inert gas and carbon dioxideis blown under the lid of the can before sealing.

3.7. Beer Dispensing

After filling and transportation the beer shouldbe stored at a temperature of 6 – 9 ◦C withoutmovement. Bottled beer should be stored in thedark. For draft beer it is important tomaintain thecarbon dioxide level established in the breweryright up to the end of dispensing, and moreoverto transfer the carbonation into the glass with-out loss. This is achieved by dispensing the beerwith a carbon dioxide pressure higher than thatof the saturation pressure in combination witha pressure compensator [46]. The clean, thin-walled glasses used exclusively for beer drink-ing should be rinsed with fresh, cold water justbefore the beer is tapped so as to equalize thetemperature. Special care should be taken in thecleaning of beer glasses in order to remove tracesof fat which might otherwise cause prematurecollapse of the sensitive foam, and also to main-tain the good flavor of the beer.

4. Properties and Quality

Foam. More than any other beverage, beeris marked by its natural ability to form foam[46]. The release of carbon dioxide during tap-ping is responsible for foam stability whereasthe sparkling of carbon dioxide bubbles in thetapped beer is responsible for head retention.Both foam stability and head retention, as wellas the liveliness of the beer, depend largelyon the carbon dioxide concentration. A foam-stabilizing effect is ascribed to colloids, such asglycoproteins, tannins,β-glucans, and isohumu-lone complexes; on the other hand, fatty acids,glycerides, and ethanol in an amount in excessof 7 – 8wt % destabilize foam.

Color. The color of beer is first of all de-termined by the malt type. During the brew-ing process an increase in color is caused bytemperature-dependent, nonenzymatic color re-actions of the Maillard type; these occur es-pecially during kilning of overmodified greenmalts treated with gibberellic acid. The beer isfurther darkened during boiling of mash por-tions and of wort, during the thermal stand ofthe wort, and also by oxidation reactions duringwort preparation and bottling. A paling of thebeer color occurs during fermentation, as wellas later during filtration.

Buffering and Reduction Potential. Thebuffering substances present in the beer arechiefly weak acids and their salts, primary andsecondary phosphates, and proteins. Dependingon their chemical identities and concentrations,they can counteract the pH changes that occurduring malting and during wort preparation, andthey can attenuate the pH drop during fermen-tation. The reductones that are formed duringmalt, wort, and beer production are of great im-portance for the stability of the beer. By addingantioxidants, the reduction potential can be in-creased further.

Sensory Qualities. The odor and the taste ofthe beer, as well as the mouthfeel, are evaluatedwith regard to quality and intensity by taste ex-perts. The temperature of the beer during tast-ing should be 6 – 10 ◦C. In a taste evaluationone differentiates between the initial impres-sion, for which the aroma and palatefullness aremainly responsible, the tingle or sparkle, wherethe impression of freshness emerges (a functionof carbon dioxide release and the organic acidspresent), and the aftertaste, where the qualityand intensity of the bitterness are put to the test.Taste expertsmust be selected carefully and theirsensory skills constantly practiced [22]. An in-ternational nomenclature with guidelines for thedescription of the impressions of beer flavor hasbeen developed [47], [48]. Five basic types offlavor evaluation methods exist [47]:

Differentiation tests are used to find out (a)if there is a difference between two or moresamples, or (b) if two or more samples areidentical to each other.

Beer 37

Descriptive tests are applied to “measure”the sensory quality of one or more samplesusing a vocabulary of flavor terms.Scaling tests rank the intensity of oneormorebeer flavor attributesPreference tests are performed by consumersto generate a simplified determination ofbeer flavor or to assess a preference.Drinkablity tests indicate the relation bet-ween the brewing process and the con-sumer’s judgement of drinkability.

Flavor Stability. After bottling the beer, nu-merous changes in its original properties occur.The changes in palatefullness and in livelinessare caused by an agglomeration of colloidal par-ticles, which in turn is facilitated by oxygen andby changes in temperature. Palatefullness de-clines, and the bitterness becomes coarser andbroader. Beer aroma undergoes a change due tonumerous reactions contributing to an “aged”quality, which is also described as oxidation orbready flavor [49], [50].

5. Analysis

5.1. Analysis of Raw Materials

5.1.1. Water

In the food-processing industry, drinking andprocess water must comply with certain qual-ity standards from the bacteriological, hygienic,and chemical point of view. The hardness of wa-ter can be determined by complexometric titra-tion, which gives an idea of the concentrationsof carbonate, hydrogen carbonate, and hydrox-ide in the water. The calcium and magnesiumhardnesses must be determined to estimate theresidual alkalinity.

5.1.2. Malt

The congress mashing method is used to studythe parameters that determine the modificationproperties of the malt. In this method, groundmalt is subjected to a simple infusion mash pro-cesswhereby the temperaturemust first bemain-tained at 45 ◦C for half an hour, and is then grad-ually increased at the rate of 1K/min to 70 ◦C;

this temperature is finally maintained for onehour.

The fine – coarse difference is calculatedfrom the drymatter extract of finely and coarselyground malt. The degree of protein modificationis the ratio of the amount of dissolved nitrogencompounds to the total nitrogen content of themalt (as determined by the Kjeldahl method).

Microscopic staining in combination withstatistical methods is being increasingly used toestimate the uniformity of modification. Otherqualitative characteristics are the enzyme poten-tial, friability, and purity of the barley variety.

5.1.3. Hops and Hop Products

The bitter ingredients can be isolated by the frac-tionation of resins or by using HPLC. Duringthe fractionation of resins, hop ingredients aredistributed between an acidic aqueous methanolphase and diethyl ether. The bitter ingredients,which are extracted into the ether phase, are clas-sified according to their solubility in methanoland hexane into total resins, soft resins, and hardresins. Depending on their ability to form leadsalts the soft resins are further classified into α-and β-fractions. Using the HPLC method eachof the homologues of the α- and β-acids andtheir oxidation products can be separated [3].

5.2. Brewhouse Control

The yield of the as-is extract (air-dried) fromthe congress mashing method is a measure ofthe yield achieved in the brewhouse during thelarge-scale preparation of the wort. For this theextract of original wort and the quantity of thecast wort must be determined.

5.3. Wort

The chemical composition of the wort is also ofinterest; amylolytic degradation and saccharifi-cation of starch components should be advancedin such a manner that only very few compoundsthat are stainable with iodine remain in the wort. When turbid lautering occurs, further stainablestarch particles are solubilized during wort boil-ing. Furthermore, turbid lautering also leads to

38 Beer

an increase in the long-chain fatty acids contentin the wort.

The gum content of the wort (determined byprecipitation with salts, or precipitating agentsor after isolation, using gel permeation chro-matography) can only slightly be influenced bythe choice of the mashing procedure. It dependsmainly on the initial gum content of the barleyand on the modification of the malt.

The degree of protein degradation duringmashing can be measured from the contents ofamino acids and dipeptides in the wort and froma fractionation of the nitrogen compounds. Theamount of coagulable nitrogen and the quantityof precipitated trub give information on the in-tensity of wort boiling. An idea of the variousMaillard reactions,which take place during boil-ing, is given by the concentrations of the aromacompounds in the wort (carbonyl compounds,alcohols, Maillard products), which are quanti-tatively determined using GC.

The isohumulones are themost important bit-ter compounds in the finished wort and in thebeer. They are extracted from the acidified sam-ple with isooctane, and their concentration is de-termined by spectrophotometry. The extinctionof the isooctane extract at 275 nm is multipliedby 50; the value thus obtained is taken as thebitterness (in EBC bitter units) according to thestandards of the European Brewery Convention(EBC) and the American Society of BrewingChemists (ASBC).

The attenuation limit is determined by fer-menting a wort sample with an excess of yeastat room temperature.

5.4. Fermentation

The most important parameters during fermen-tation are the decrease in extract, the pH, and thetemperature. The practice of keeping a record ofthe yeast cell concentration from pitching to theend of fermentation using the electronic Coultercounter or microscopic count methods (Thomachamber) is gaining increasing importance.

Gas chromatographic methods have provedto be useful in estimating the aroma compo-nents. Whereas the more concentrated fermen-tation byproducts in the ppm-range can be usedto judge the fermentation and eventually occur-ring organoleptic deviations, certain trace com-

ponents in the ppb-range can serve as indicatorsubstances for the identification of the processtechnology. The acetoin concentration is usedas an indicator for the vitality of the yeast. Aftera relatively simple work-up method (steam dis-tillation of the sample followed by extraction ofthe distillate with dichloromethane) about 60 in-dividual components can be detected in a singlerun using modern GC and high-resolution cap-illary columns. Along with selective detectors(sulfur detector, nitrogen detector), this figurecan be increased considerably.

5.5. Microbiological Process Monitoring

In a brewery the main contaminants are lac-tobacilli, Pediococcus cerevisiae, and “wildyeasts” (Saccharomyces species). Gram-negative bacteria (genusMegasphaera or Pecti-natus) may also be dangerous [24].

Direct viewing under themicroscope, biolog-ical shelf life tests, and enrichment methods areused. Shelf life tests show microbiological sta-bility of the beer during a storage at 27 ◦C. Theyeast sediments of samples taken from the fer-mentation and the storage cellars are observedunder the microscope after a period of about 20days. In the case of filtered samples, trace in-fections are detected by enrichment on a solidor liquid nutrient medium. By using membranefiltration techniques, the microorganisms on thefilter are incubated anaerobically under optimalgrowth conditions on solid agar. The samplescan be evaluated after an incubation period oftwodayswith aerobic incubation (wort agar) andfive days (NBB agar; NBB= culture medium forbacteria harmful to beer) with anaerobic incuba-tion. Color changes in liquid NBB broth or solidNBB agar indicate the presence of harmful bac-teria.

The number of biological controls and thechoice of culture media depend on such factorsas selectivity, specificity, and output of the brew-ery. As a routine procedure, the pitching yeast aswell as bottled beer stored for a specific periodshould be analyzed.

5.6. Beer

The extract of original wort of the finished prod-uct can be calculated from the density and re-

Beer 39

Table 8. Beer production, exports, imports, consumption and per capita consumption in 2000 (countries are ranked in the order of decreasingoverall consumption

Production, Exports, Imports, Consumption, Per capitaconsumption,

106 hL/a 106 hL/a 106 hL/a 106 hL/a L/a

1. United States 213.1 2.7 23.3 235.9 86.12. China 223.1 0.8 0.8 223.1 17.23. Germany 113.3 11.1 3.2 105.4 128.04. Brazil 86.6 0.5 0.1 86.2 51.25. Japan 71.1 0.5 0.9 71.5 56.26. United Kingdom 55.2 3.7 5.5 57.0 95.97. Mexico 57.8 7.9 0.5 50.4 48.98. Russia 48.8 0.3 0.4 48.9 33.69. Spain 26.4 0.6 2.7 28.5 72.010. South Africa 24.2 0.3 0.5 24.4 55.516. Czech Republic 18.0 1.7 0.2 16.5 160.621. Netherlands 25.1 12.9 0.9 13.1 82.827. Austria 8.8 0.5 0.5 8.9 110.534. Denmark 8.1 2.6 0.1 5.6 106.135. Ireland 8.0 3.1 0.7 5.6 150.5

Americas 473.8 57.3Europe 463.6 53.2Asia/Pacific 384.9 11.2Africa 64.1 6.4

World total 1386.3 22.6

fractive index of the decarbonated beer or fromthe densities of beer distillate and the distillationresidue.

Themethods described in Section 5.3 are alsoused for beer. The carbon dioxide content is de-termined by measuring the total pressure of beerafter vigorous shaking at a specific temperature.

The physicochemical stability of the beer isestimated from an accelerated aging process. Inthis method filled beer bottles are kept alter-nately at 40 ◦C (or at 60 ◦C for stabilized beer)and at 0 ◦C until an increase of turbidity by 2EBC formazine units occurs after cooling. Bymultiplying the obtained stability period – ex-pressed as 40 ◦C- (or 60 ◦C-)warm days – witha factor that is specific to each brewery, one cancalculate the period of time during which thebeerwould not become turbid under normal stor-age conditions.

The carbon dioxide content of the beer deter-mines its foaming capacity. The head retentionis dependent on the composition of the beer. Themethods of foammeasurement are classified ac-cording to the way the foam is generated: (1)free fall, (2) shaking, (3) bubbling of a gas, and(4) catalytic release of carbon dioxide.

Color can either be measured by visual com-parison under defined conditions or spectropho-tometrically by measuring the extinction of the

sample at 430 nm and that at 700 nm; this differ-ence, multiplied by 25.5, is defined as the colorin EBC color units.

5.7. Legally Required Controls

In order to comply with the requirements of thefood laws, the extract of original wort or thealcohol content must be within certain limits.Further, the filling volume in the bottles mustbe within required tolerances. Nevertheless, itis still indispensable that the brewmaster is re-sponsible for determining by taste test whetherthe beer is ready for filling and before it leavesthe brewery.

In the last years breweries introduced inte-grated management systems and had them val-idated by a external accredited and recognizedcertification body. The following systems havebeen introduced [51], [52]:

Quality Management Systems in accordancewith DIN EN ISO 9001 (design, develop-ment, production, installation, and mainte-nance),Environmental Management System in ac-cordance with DIN EN ISO14001,Working Security System, and

40 Beer

Table 9. Top world breweries

Production, 106 hL/a Regional ranking Leading brands

Names Output, 106 hL/a

1. Anheuser – Busch (USA)124.1 Americas no. 1 Budweiser 51.9

Bud 39.9Busch 17.1

2. Heineken (Netherlands)74.8 Europe no. 1 Heineken 21.6

Africa no. 2 Amstel 10.83. Interbrew (Belgium) 64.1 Europe no. 3 Stella Artois 7.0

4. Brahma/AmBev (Brazil)62.4 Americas no. 2 Skol 25.4

Brahma Chopp 20.9Antarctica 20.9

5. South African 61.3 Africa no. 1 Castle Lager 14.4Europe no. 5

6. Carlsberg (Denmark)60.9 Europe no. 2 Carlsberg 10.0

Baltika 8.07. Miller (USA) 50.6 Americas no. 3 Miller LITE 19.6

Miller Genuine Draft 9.18. Kirin (Japan) 38.5 Asia/Pacific no. 1 Kirin Lager 11.1

Tanrei –Nama 8.49. S&N-Kronenbourg (France) 36.8 Europe no. 4 Kronenbourg 6.610. Modelo (Mexico) 36.6 Americas no. 4 Corona 24.1

Hazard Analysis Critical Control Points (hy-giene in food producing companies)

6. Economic Importance

During the period of 1991 – 2000 beer outputincreased by more than 20 % worldwide. De-spite stagnation in several large beer consumingnations the total market size of 1386× 106 hLreached a new peak in 2000. The per capita con-sumption increased only marginally, to reach22.6 L in 2000 [27].

Themost popular product is the pale, bottom-fermented lager of typically 4.5 – 5.5 vol% alco-hol. Worldwide 65 % of the beer is marketed inbottles, 22 % in cans and 13 % in kegs or barrels(draught beer).

Because the cereals produced in the individ-ual countries are not exclusively used formaltingand brewing, it is not possible to list which andhow much of the different cerials are used. Theworld crop of hops in 2001 was 97 730 t (62 %bitter hops, 38 % aroma hops). The content ofα-acids was about 8 % on average, so 7928 tof α-acids were harvested. Production and con-sumption figures are given in Table 8, Table 9lists the top brewers of the world and their lead-ing brands.

A survey of the productivity and quantitiesof energy and water consumed in breweries ofdifferent sizes is given in Table 10.

Table 10. Productivity and specific energy and water comsumptionas an function of brewery size

Breweries with an annual output of

> 106 hL > 105 hL > 104 hL

Productivity, hLper employee

7000 3000 1000

Currentconsumption,kWh/hL

8 10 13

Heatconsumption,kWh/hL

30 40 50

Waterconsumption,hL/hL

4 6 8

Taxation. The varieties of beer are classifiedinto various tax groups on the basis of their ex-tract of original wort or alcohol content. Thegroups differ from country to country. Thereare different means of tax collection: (1) raw-material taxation, which is based on weight orvolume of the brewing materials used; (2) in-termediate product taxation, which is assessedaccording to the volume of the wort, and (3) fin-ished product taxation, which is levied on salesbeer.

Beer 41

7. Physiology and Toxicology

According to standard definitions, beer is clas-sified as a food. In addition, it acts as a stim-ulant. The calorific content of beer as a nutri-ent may be calculated from its concentrationsof protein, carbohydrate, and alcohol, as well asorganic acids. A rough estimate in kJ/L can beobtained by multiplying the extract of originalwort (in wt %) by a factor of 150. Hence beerswith 10 – 14 % extract of original wort have anapproximate calorific value of 1500 – 2100 kJ/L.From a nutritional point of view, the aminoacids (on an average 140mg/L) and vitamins(20 – 25mg/L) are especially valuable. One literof beer contains about 40µg thiamine, 400µgriboflavin, 7500µg niacin, 650µg pyridoxine,1500µg pantothenic acid, and 800µg folic acid.

The consumption value of beer may bederived from its ingredients. Thirst quench-ing is accomplished by its high water con-tent and its mineral concentration (total around1000mg/L, consisting of: sodium 20 – 30mg/L,potassium 500mg/L, calcium 30mg/L, phos-phorus 300mg/L, and magnesium 100mg/L).Carbon dioxide (4 – 8 g/L) and organic acids (upto 600mg/L) have a relaxing, calming and, at thesame time, stimulating effect. The dietetic effectof the beer is based mainly on its low sodiumconcentration. Because it also is free of fats, itwill promote urination.

Pathogenic and toxic bacteria cannot survivein beer because of the presence of alcohol, car-bon dioxide, bitter substances, and the low pH.A proper balance between alcohol and assim-ilable carbohydrates, proteins, phosphates, andvitamins results in a lower increase in blood al-cohol levels by comparison with other alcoholicbeverages. The toxicology of ethanol is treatedelsewhere (→Ethanol, Chap. 11.).

Benefits of Moderate Beer Consumption.Beer as a wholesome beverage has formed a sta-ple part of human diet for thousands of years.When consumed moderately and regularly beeris not only enjoyable to drink, but also benefi-cial to health. A daily consumption of 60 – 80 galcohol (corresponding to 1.5 to 2 L of beer) bya healthy, adult male, or 40 – 60 g alcohol by anadult woman is not harmful. These guidelinesvary according to body weight, age and nutri-tional habits as well as physiological condition.

Rules for reasonable beer consumption are givenin [53], [54].

It has been shown inmany studies throughouttheworld thatmoderate consumption of beer – incontrast to heavy drinking or abstention – is pro-tective against cardiovascular diseases such asheart attack and some forms of stroke [55]. Oneexplanation for this effect is that beer increasesthe level of “goodHDL cholesterol” in the blood[56], another explanation is that alcohol reducesblood coagulation [57]. Beer is reported to pro-tect against gallstone formation [58], diabetes[59], and even osteoporosis [60]. Hops containactive compounds which prevent calcium de-pletion of bones. Beer drinkers are protectedagainst Heliobacter pylori bacteria [61], whichcause stomach ulcers and may increase the riskof stomach cancer. Beer is also a source of solu-ble fiber (5 – 10mg/L), originating from the cellwalls ofmalted barley.A liter of beer contains onaverage 20 % of the recommended daily intakeof fiber. Fibers do not only support a healthybowel function, they also retard the digestionand adsorption of food, and lower cholesterollevels, whichmay help to reduce the risk of heartdiseases [62].

Beer is also a source of antioxidants(200 – 600mg phenolic carboxylic acids,flavonoids and tannoids per liter of beer), whichshow a cancerostatic activity [63–65]. Addi-tional research has shown that the antioxidantspresent in beer are more readily available tothe body than those from solid foods [66]. Fur-thermore, beer contains a large amount of di-etetically valuable silicon as orthosilicate, itsbiologically available form. The silicon contentof the human body has a direct effect on themineralization of the bones and the density ofthe bonemarrow. Beer contains 10 – 40mg SiO2per liter, which is absorbed to more than 50 %by the human body. Thus beer is one of the mostimportant dietetic silicon sources.

Harmful Substances. Numerous nutritionalregulations require the amount of additives inbeer to be kept to a minimum.Heavy metals derived from rawmaterials are

mostly removed during the malting and brew-ing process; beer is one of the beverages low-est in heavy metals (lead, 1 – 3µg/kg; cad-mium, 0.1 – 0.5µg/kg;mercury, always less than0.1µg/kg). Mycotoxins and insecticides have

42 Beer

not been found in beer until now. Fungicidesprays, especially dithiocarbamates, are usedin hop growing. The residues contained in thehops are metabolized during wort boiling toethylenethiourea and propylenethiourea, whichare only partially removed in the further brew-ing process and remain in the beer. The neces-sary sprayings could be reduced considerablyby breeding spore-resistant types as well as byan early warning system. The concentrations ofresidue can also be cut to less than 5mg/kg byallowing a time lapse of several weeks betweenthe last spraying and the actual harvesting. Vari-ous hop extraction procedures also can lower theconcentration of dithiocarbamates.

The World Health Organization (WHO) rec-ommends a limit of nitrates of 50mg per liter ofdrinking water. The nitrate in the wort originatesmainly from water and hops. Nitrate is reducedto nitrite, which is poisonous to yeast. However,its concentration is much below the thresholdconsidered critical by theWHO. The concentra-tion of nitrate in beer corresponds to that of thebrewing water. Nitrate can be most effectivelyremoved from the water by anion exchange.

The concentration of highly carcinogenic N-nitrosodimethylamines is virtually negligible,because kilns are fired indirectly nowadays.With average values of less than 0.5µg/kg, beerproduced today is no longer significant as a po-tential source of nitrosoamines.

The byproducts formed during fermentation,such as higher alcohols, esters, and aldehydes,are of more importance for the aroma of the beerthan for its wholesomeness. No connection canbe found between the level of higher alcohols,fats, and aldehydes and the incidence of hang-over.Sulfur dioxide is a true fermentation byprod-

uct. Bottom-fermented lager or pilsener contain0 – 10mg/kg, top-fermented beers 0 – 5mg/kg,whereas strong beers may contain more than10mg/kg of the gas. The source cannot be tracedback to the sulfur content of the malt, the hops,or the brewing water.Histamine, a metabolite of histidine, occurs

in beer in amounts of under 0.5mg/kg, and hasno toxic effect at this level. The nucleic acidcomponents of beer originate from the raw ma-terials. The yeast needs adenine and guanine forits growth and removes part of these substancesduring fermentation. The purines of the finished

beer are broken down to uric acid in the humanbody, which can cause gout if the amount ex-ceeds the solubility in blood. Bottom-fermentedlager beers contain 70 – 130mg purine per kilo-gram; in wheat beers the figure is around80mg/kg [67].

8. References

General References1. B. E. Briggs: Malts and Malting, Chapman &

Hall, Andover 1997.2. H. J. Barth, C. Klinke, C. Schmidt: Der großeHopfenatlas/The great hopatlas, Verlag HansCarl, Nurnberg 1994.

3. M. Verzele, D. De Keukeleire: Chemistry andAnalysis of Hop an Beer Bitter Acids, ElsevierScience Publishers B.V., Amsterdam 1991.

4. J. L. Benitez et al.: Hops and Hop Products,Verlag Carl Hanser, Nurnberg 1997.

5. G. Reed, T. Nagodawithana: Yeast Technology,2nd ed., Van Nostrand Reinhold, New York1991.

6. C. P. Kurtzman, J.W. Fell: The Yeasts, 4th ed.,Elsevier Science Publishers B.V., Amsterdam1998.

7. L. Narziß: Abriß der Bierbrauerei, 6th ed., F.Enke Verlag, Stuttgart 1995.

8. L. Narziß: Technologie der Malzbereitung, 7thed., F. Enke Verlag, Stuttgart 1999.

9. L. Narziß: Technologie der Wurzebereitung,7th ed., F. Enke Verlag, Stuttgart 1992.

10. K.U. Heyse (ed.): Handbuch derBrauereipraxis, 3rd ed., Verlag Hans Carl,Nurnberg 1994.

11. K.U. Heyse (ed.): Praxishandbuch derBrauerei, B. Behr’s Verlag GmbH & Co.,Hamburg 2000 and supplements.

12. W. Kunze: Technologie Brauer und Malzer,8th ed., Verlag der VLB Berlin, Berlin 1998.

13. W. Kunze: Technology Brewing and Malting,2nd ed., Verlag der VLB Berlin 1999.

14. T. Wainright: Basic Brewing Science,Wainright, Reigate 1998.

15. European Brewery Convention Monographs:Separations Process 1990, Packaging 1990,Wort Boiling and Clarification 1992, WasteReduction in Brewery Operations 1992,Instrumentation and Measurement 1992,Process Hygiene 1994, Hops 1994, MaltingTechnology 1994, Immobilized YeastApplications in the Brewing Industry 1995,Draught Beer ∗Packaging∗ Dispense 1996,

Beer 43

Quality Issues & HACCP 1997, Beer FoamQuality 1998, Yeast Physiology – a new Era ofOpportunity 1999, Assuring Product Safety inthe Brewing Industry 2000. Verlag Hans Carl,Nurnberg.

16. European Brewery Convention Proceedings:23rd Congress, Lisbon 1991, 24th Congress,Oslo 1993, 25th Congress, Brussels 1995, 26thCongress, Maastricht 1997, 27th Congress,Cannes 1999, 28th Congress, Budapest 2001,University Press, Oxford.

17. N. Buchner: Verpackung vonLebensmitteln – Lebensmitteltechnologische,verpackungstechnische und mikrobiologischeGrundlagen, Springer Verlag, Berlin,Heidelberg 1999.

18. O.G. Piringer, A. L. Baner: Plastic PackagingMaterials for Food, Wiley-VCH, Weinheim2000.

19. Deutscher Brauerbund: Leitfaden“Schankanlagen” (1997).

20. P. Dilly: Qualitatssicherung in der Brau- undGetrankewirtschaft, B. Behr’s Verlag,Hamburg 1990.

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Bentonite → ClaysBenzal Chloride → Chlorinated Hydrocarbons