Maintaining Ideal Yeast Health: Nutrients Yeast Need

8/9/2019 Maintaining Ideal Yeast Health: Nutrients Yeast Need

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Maintaining Ideal Yeast Health:Nutrients Yeast Need


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What makes a great beer?

Fermentation. You put the yeast in, and then thefermentation takes about a week. A lot happens in that

week. The trick is to give the yeast exactly what it

wants. Its a mould and it wants to eat, and while it

eats, it makes alcohol and gas.

Interview with Eric Molson; Globe and Mail, May 29, 2009

Eric Molson


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General concept

Wort

nutrients

Yeast

Beer


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Importance of Yeast toBeer Characteristics

Around 950 compounds arethought to give beer its character

Of these, around 400 are producedby yeast!


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WORT(sugars, amino acids, etc.)

Acids (organic & fatty)

Alcohols (ethanol

& fusel oils)

Glycerol

Esters

Aldehydes & ketones

Sulphur compounds

Phenols

Yeast autolytic

compounds

CO2

More yeast!


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Elemental requirements for

growth of brewing yeast

H - cell water, organic materialO - respiration, cell water, organics

C - organic material

N -proteins, nucleic acids, coenzymes

S -proteins, coenzymes

P - nucleic acids, phosphoslipids

K - cell electrolyte, enzyme cofactor

Mg - enzyme cofactor, cell division

Ca - flocculationMn - enzyme cofactor

Fe - cytochromes

Zn - alcohol dehydrogenase

Co - vitamin B12, coenzymes

Cu, Ni, Mo - specialisedenzymes

Macroelements Microelements


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Yeast nutrients in wort Carbohydrates (fermentable sugars) Nitrogen sources (mainly amino acids)

Inorganic sources (P, S, Mg, Zn, other minerals)

Oxygen (need around 25% saturation of wort)

Yeast foods(vitamins, fatty acids, sterols)

NOTE: The level and availability of such nutrients is very

important in governing fermentation performance of brewingyeast


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Wort composition influences:

Rate of attenuation Degree of attenuation

Amount of yeast produced

Flocculation

Beer characteristics


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Carbon sources for brewingyeast Hexose sugars: glucose, fructose

Pentose sugars: no (but possibly xylulose)

Disaccharides: maltose, sucrose, melibiose

Trisaccahrides: maltotriose (slowly) Tetrasaccharides: maltotetraose (possibly some strains)

Oligosaccharides: maltodextrins (unfermented)

Polysaccharides: starch (unfermented)

Others: ethanol, acetate, glycerol (only respired)


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Nitrogen sources forbrewing yeast

Peptides Amino acids

Ammonium salts (little present inwort)


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Inorganic sources forbrewing yeasts

Phosphorus, sulphur and potassium generally

sufficient in wort

Metal cations may occasionally be deficient (andratios of metal ions may be sub-optimal)

Essential bulk ions: K, Mg

Essential trace ions: Zn, Ca, Fe, Mn

Toxic trace ions: Pb, Cd, Cr, Hg, Cu etc.


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Zinc Faster fermentation

Better flocculation

Stimulates uptake of maltose and maltotriose

Stimulation of protein synthesis and yeastgrowth

Protection of enzymes

Stabilisation of protein and membrane system


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Zinc Concentration in Wort

During wort preparation approx. 95 % of zincfrom malt are lost with spent grain

In modern stainless steel breweries the zinc

concentration is not sufficient (


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Zinc wort content is almostzero after 1 hour

Zn is entirely accumulated intocells which redistribute the metalamong growing yeast

LAGER strain-25C

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12 14 16 18 20 22 24

Time (h)

Zncellassociated(fg/cell)

0

0.06

0.12

0.18

0.24

0.3

0.36

0.42

0.48

0.54

0.6

Znsupernata

nt(ppml)

Cell Supernatant

LAGER strain-25C

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7

Time (h)

PercentageZncellassociated(%

)

Lager brewingyeast strain labconditions

G. Walker, ASBC 2007, Victoria, Canada


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Zn & fermentation performanceZn & fermentation performance

Low zinc (0.05 ppm)Low zinc (0.05 ppm)delaydelayeded sugar utilizationsugar utilization

High zinc (10 ppm) slightlyHigh zinc (10 ppm) slightly

delaydelayeded sugar utilizationsugar utilization

but same after 14 daysbut same after 14 days

fermentationfermentation

0.4 ppm0.4 ppm--1.0 ppm Zn1.0 ppm Zn

resultresulteded in fastestin fastestfermentation ratesfermentation rates

1.000

1.010

1.020

1.030

1.040

1.050

1.060

0 48 96 144 192 264

Time (hours)

Specificgravity

0 0.05 0.12 0.48 1.07 10.8 (Zn ppm)

0

1

2

3

4

5

6

7

48 96 144 192 264Time (hours)

Ethanol(%)

0 0.05 0.12 0.48 1.07 10.83 (Zn ppm)

Specific gravitySpecific gravity

EthanolEthanol

G. Walker, ASBC 2007, Victoria, Canada


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Vitamin sources forbrewing yeasts

Wort generally sufficient in folic acid,thiamine, riboflavin, pantothenic acid,niacin, inositol and biotin

Biotin, however, may occasionally bedeficient

Can supplement wort with yeast foods


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Typical levels of vitamins

in wortVITAMIN LEVEL IN

WORT /100mlMETABOLICROLES

Biotin 0.5g Carboxylations

Thiamin (B1) 60g Decarboxylations

Pantothenate (B5) ~50g Acetylations, CoA

Nicotinic acid (B3) 1000g Coenzymes

Riboflavin (B2) 50g Coenzymes

Pyridoxine (B6) 85g Amino acidmetabolism

Inositol 10mg Membranes


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Yeast transport strategies for

wort nutrients

WORT

NUTRIENTS

?

YEASTMETABOLITES

(beer)

?

Yeastcell


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Translocation of wortnutrients into brewing yeast

CELLULAR BARRIERScapsule, cell wall, periplasm, plasma membrane,

organelles

PHYSICO-CHEMICAL BARRIERS

chelation, adsorption, molecular size, binding

(e.g. nutrient unavailability in wort particles)


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PHYSICO-CHEMICAL

BARRIERS Zinc chelates with phytic acid, proteins &

polyphenols

These complex compounds are very stable

Only ionic zinc is available to yeast

Regular AAS is a destructive method, whichmeasures total zinc not available zinc

Ion-exchange separation separates complexand ionic zinc before AAS


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Derived from: Vecseri-Hegyes, B., P. Fodor, et al. (2005). "The Role of Zinc in Beer Production, I(Wort Production)." Acta Alimentaria 34(4): 373-380.

Total and complex zinc concentration of industrial wort samples

0

0.02

0.04

0.06

0.08

0.1

0.12

1 2 3 4 5 6

zincco

ncentration[mg/L]

total zinc

complex zinc

available zinc


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Consequences of low

assimilable nitrogen wort

Low available nitrogen, especially in

very high gravity wort, below athreshold of around 150mg/L, may

lead to stuck fermentations


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Amino acid uptake by brewing

yeast

GROUP A (fast)

Glu, Asp, Asn, Gln,

Ser, Thre, Lys, Arg

GROUP C (slow)

Gly, Phe, Tyr, Try,

Ala, NH3

GROUP B (intermediate)Val, Met, Leu, Isoleu, His

GROUP D (little or no)

Pro

NOTE: A variety of transport permeases

exist for (active) amino acid uptake by brewing yeast


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Yeast growth vs. Diacetyl Levels

Synthesis of valine/leucine required

acetolactate produced

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7

Days Fermentation

Yeast

Growth

0

0.1

0.2

0.3

0.4

0.5

0.6

0.70.8

0.9

1

Dia

cetyl

Degrees Plato

Yeast growth g/L

Diacetyl (mg/L)

Valine/Isoleucine synthesis required

-acetolactate produced


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Mechanisms for yeast food enhanced

reduction of diacetyl levels?

- acetolactate diacetyl

By-product of valine

and isoleucine synthesis

by yeast

acetoin

Oxidative

Decarboxylation

(Slow)

Yeast reductase - fast

Requires functioning cell membrane

to allow for uptake of diacetyl prior

to reduction

Amino acids supplied by yeast foodsMay reduce requirement for synthesis

of valine/isoleucine (and thus - acetolactate

and diacetyl production)?

Provision of usable nitrogen sourceplus other nutrients results in a more

vital cell that is enhancing diacetyl

uptake and reduction?


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Yeast nutritionpotential problems for fermentation

Spectrum/availability of wort sugars

e.g. High glucose worts may slow fermentation

Insufficient FAN

Stuck fermentation, change in flavour profile

Metal ion availabitiy e.g. Low Zn, excess Ca, insufficient Mg, toxic Cu

Vitamin deficiency(e.g. pantothenate - sulphur off-notes)

Stressed yeast - impaired nutrient uptake(ethanol, pH, CO2, temp., starvation, osmotic pressure.)


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Yeast Foods


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Commercial Yeast Foods

Available Components Amino acids (FAN)- as protein hydrolysate or added as

individual amino acids

Low molecular weight peptides

NH4+

Growth factors (vitamins)

Protein (non-utilisable) active in CO2 nucleation? Sulphur/Phosphorous

Zn/Cu/Mn/Ca (enzymatic and structural roles)

Yeast hulls (broken cell walls) as sterol/FA source,nucleation site

Ergesterol expensive


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Typical Yeast Food Effects* Improved alcohol yield (increased extract

utilization)

Reduction in fermentation time (12-24h)

Enhanced yeast vitality Protect against stress

Enhanced diacetyl removal/consistent diacetylspecification

Control of undesirable flavour compounds

* Depending on the yeast food composition


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Nutrient Trial ResultsEastern European Brewery A

6.86.3

71

98

34.9 33.2

0

10

20

30

40

50

60

70

80

90

100

Primary Fermentation

Time (days)

VDK in specification at

time (%)

Average Diacetyl (ppb)

Control

Nutrient


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Nutrient Trial ResultsEastern European Brewery B

4 6

148

87

3.7 3.3

0

20

40

60

80

100

120

140

160

Primary Fermentation Rate

(degP/Day)

Final Diacetyl Level (ppb) Residual Extract

Control

Nutrient


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Servomyces

Weihenstephan Trials15L lab trials Sample 1: no zinc addition (O-wort)

Sample 2: addition of 0.3 mg/L ZnCl2

Sample 3: addition of 8 mg/L inactive yeast

Sample 4: addition of 8 mg/L SERVOMYCES

Sample 5: addition of 2.3 mg/L SERVOMYCES

Sample 6: addition of 8 mg/L inactive yeast + 0.3 mg/L ZnCl2 Initial yeast zinc pool: 4.1 mg/100 g

3.115.1311.612.634.152.67Crop yeast

[mg/100 g]

0.340.361.220.110.350.10Initial wort

[mg/L]

inactive yeast

+ ZnCl2

SERVOMYCES

Low Addition

SERVOMYCES

High Addition

inactive

yeastZnCl20-wort


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ServomycesWeihenstephan Trials

Fermentation in 15L CCT at 10 C

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7 8 9

fermentation days

Extract[

Plato]

ZnCl

inactive yeast

Servomyces - high addition

0-Wort

Servomyces - low addition

inactive Yeast + Zn Cl


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Servomyces Trial ResultsUS Brewery

4

5

6

7

8

9

10

11

12

13

14

0 1 2 3 4 5 6

Fermentation days

Extract[B

rix]

Servo addition A Servo addition B

No Servo A No Servo B


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Propagation With each cell division the internal zinc pool is

divided between mother and daughter cell

Fermentation 4-5 times biomass increase

Propagation 15-20 times biomass increase

=> very low internal zinc pool

Slower, less efficient propagation

Fermentation problems in 1. generation beer

Slower, stuck fermentation Longer diacetyl rest

Less flocculent yeast


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The Impact of Nutrients on

High Gravity/Adjunct Brew

60% malt / 40% adjunct / 18P / Gen 1

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0 1 2 3 4 5

time [day]

Extract[%w

/w

]

Control A F

B D C

E


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Serial Repitching Repeated stress for the yeast

Decline in yeast activity

Resistance to stress is strain

dependent

Contamination

Genetic drift/petite mutation

The Impact of Yeast Generation on the


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The Impact of Yeast Generation on the

Use of NutrientsHigh Gravity/Adjunct Brew

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0 1 2 3 4 5

time [day]

Extract[%

w/w]

Control A F

B D C

E

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0 1 2 3 4 5 6 7 8 9

time [day]

Extract[%

w/w]

Control A F

B D C

E

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

time [day]

Extract[%

w/w

]

Control A F

B D C

E

Gen 1 Gen 6

Gen 8


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Nucleation SitesEffect of dissolved CO2

Inhibits growth and metabolism

Decreases multiplication rate

Reduces biomass yield

Increases lag phase

Inhibition of nutrient uptake

Loss of cell division and bud formation


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Nucleation Sites Particles working as nucleation sites reduce the

solubility of CO2

Most nucleation in a fermenter occurred fromparticles that sedimented to its bottom

Particle size is a likely determinant of theparticles ability to be an effective CO2 nucleator

The more porous a particle is, the most efficient itis as a nucleation site

Soy flour may be ruled out due to allergen issues

N l i Si D i


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Nucleation Sites Degassing

Activityreleased CO2after 2.5 hours

Control Soy Flour A B C0

1

2

3

4

CO2[g/L

]


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Maintaining Ideal Yeast Health: Nutrients Yeast Need