Cheese Re )

CRC PR ESSBoca Raton London New York Washington, D.C.

Cheese Rheolog yand Texture

Sundaram GunasekaranM. Mehmet Ak

2003 by CRC Press LLC

This book contains information obtained from authentic and highly regarded sources. Reprinted materialis quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonableefforts have been made to publish reliable data and information, but the authors and the publisher cannotassume responsibility for the validity of all materials or for the consequences of their use.

Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronicor mechanical, including photocopying, microfilming, and recording, or by any information storage orretrieval system, without prior permission in writing from the publisher.

The consent of CRC Press LLC does not extend to copying for general distribution, for promotion, forcreating new works, or for resale. Specific permission must be obtained in writing from CRC Press LLCfor such copying.

Direct all inquiries to CRC Press LLC, 2000 N.W. Corporate Blvd., Boca Raton, Florida 33431.

Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and areused only for identification and explanation, without intent to infringe.

Visit the CRC Press Web site at www.crcpress.com


No claim to original U.S. Government worksInternational Standard Book Number 1-58716-021-8

Library of Congress Card Number 2002034861Printed in the United States of America 1 2 3 4 5 6 7 8 9 0

Printed on acid-free paper

Library of Congress Cataloging-in-Publication Data

Gunasekaran, Sundaram, 1957-Cheese rheology and texture / Sundaram Gunasekaran, M. Mehmet Ak.

p. cm.Includes bibliographical references (p. ).ISBN 1-58716-021-8 (alk. paper)1. CheeseTexture. I. Ak, M. Mehmet. II. Title.

TX382 .G86 2002637.3dc21 2002034861


Dedication

To:

My parents, Raga Palanisamy Sundaram and Kamala Sundaram, for inspiring me to always strive for excellence.

My wife, Sujatha, and children, Suvai and Suman,for their love, support, and patience.

SG

My father, Haci Ak, and mother, Zeynep Ak,for giving me the opportunities they never had.

My wife, Nese, who continuously supported my efforts and patiently endured the time I spent working on this book.My daughter, Asli, and my son, Efe, who cheered me up

in times the situation looked hopeless.

MMA


ForewordTwo complex scientific areas, cheese and rheology, create an exponential increasein complexity when combined. This text makes a significant contribution to anunderstanding of this complexity. It underscores limitations and considerations inevaluating and conducting research on cheese rheology, points out some importantgaps in our understanding of cheese rheology, and thoroughly reviews methods,theories, and applications of rheology in general and specifically for cheese.Rheologists will gain a better understanding of the physicochemical properties ofcheese, and cheese researchers will be exposed to the wide range of rheologicalmethods and the theoretical bases of those methods. Both groups should realizethe need for collaborative research after exposure to the individual complexities ofcheese and rheology.

The diversity of observations, and seemingly contradictory observations, on thephysical and chemical properties of cheese that appear in this text should not besurprising since many of the observations were made before instruments wereimproved and were specifically adapted to deal with unique properties of cheeses.Also, confusion resulted from: cheese scientists who used techniques inadequateto definitively measure physical properties of cheese; rheologists who chose testsamples of cheese that did not possess comparable chemical properties except forthe property to be measured; and inadequately defining the chemical properties ofcheese. The authors have discussed unique characteristics of cheese that rheologistsshould be cognizant of in designing experiments. Comments on merits and deficien-cies of wide range of rheological test methods as applied to cheese should assistcheese scientists in appropriately using the procedures. The chronology of cheeserheology research outlined in this book is encouraging as evidenced by the increasein collaborative research groups or research groups with better understanding ofboth research areas.

The physicochemical properties of cheese have always been an important com-ponent in assessing cheese quality and value. The assessment was usually done bysensory evaluation, which was quite adequate because cheese was generally con-sumed in its original state. Development of heat-processed cheese products in theearly 1900s prompted some research on the physical properties of cheese, primarilyby modifying chemical properties, however, only limited research was done onrheological properties. The last several decades have greatly changed the forms anduses of cheese in the market place. Cheese has to be sliced or shredded by high-speed cutting devices; the melt and flow properties of cheeses have to be morecarefully controlled; flavor intensities and flavor profiles have to be modified withoutadversely affecting physical properties of cheese; and cheese products must possessadequate stability, often under wide ranges of environments. This myriad of desiredproperties greatly increases the need for procedures to independently control specificproperties and the need for adequate methods to measure the properties specifically


being controlled. The authors of this book have facilitated attainment of these goalsby their thorough review of the present status of cheese rheology research and byproviding guidance for further research efforts.

Norman F. OlsonDepartment of Food Science and Center for Dairy Research

University of Wisconsin-Madison


PrefaceRheology of cheese has been studied since the early 1950s. In fact, Cheese Rheologyis the name of a chapter in the 1958 FAO Report*. Since then, many advances havetaken place both in cheese technology and rheology. As cheese became an importantpart of the diet in many parts of world, the cheese industry responded by manufac-turing new types of cheeses with varying textures to suit varied needs and to promotecheese use both as a table cheese and as an ingredient food. This flurry of newcheeses and applications and cheesemaking technologies has also brought about anacute need to characterize the rheological and textural attributes of cheeses to ensuretheir high quality. Thus, for food rheologists and food scientists, cheese is amongthe most popular subjects of study.

In this book, we have attempted to summarize the vast literature available oncheese rheology and texture. Needless to say, the sheer volume of informationavailable and the complexity of both cheese and rheology made this a particularlydifficult task. Our goal was to bring together many of the dispersed publishedinformation on cheese rheology and texture in one book to serve as a comprehensivereference source. A unique aspect of this book is that it contains detailed descriptionsof several methods to study rheology of foods in general and cheese in particular.This is to provide the interested readers the necessary basic information on manytechniques reported in the literature which often do not have adequate explanation.

Chapter 1 provides an overview of cheesemaking technology. Fundamentalrheological test methods are described in much detail in Chapter 2. This chapterwill facilitate the readers to gain a deeper understanding of the various rheologicaltest methods. The uniaxial testing, one of the most widely used classes of rheologicaland texture testing methods, is the focus of Chapter 3. The fracture mechanics arean extension of the uniaxial test methods. These are discussed in Chapter 4. InChapter 5, linear viscoelastic methods are described. This is now among the mostpopular rheological test performed on cheeses, and is also known as dynamic testing.Both the theory and applications are discussed in a manner benefiting those whoare already familiar and those who are new to the subject. Chapter 6 focuses onnonlinear viscoelasticity of cheeses. This subject has not received much attentiondue to the lack of available instrumentation and the complexity of data analysis.This chapter will be more useful to those familiar with rheological analysis than tothe casual reader. The discussion on cheese texture in Chapter 7 is limited tomechanical texture of cheese, as it is more in line with rheological measurements.Cheese meltability and stretchability, two of the most important properties of cheeseused in prepared foods, are the topics of Chapters 8 and 9. The emphasis in thesechapters is on measurement methods. The effects of various factors on cheesefunctional properties are addressed in Chapter 10.

* Kosikowski, F.V. and G. Mocquot. 1958. Advances in Cheese Technology, FAO Studies No. 38. Foodand Agriculture Organization of the United Nations. Rome, Italy.


Acknowledgments

We would like to acknowledge many individuals who have contributed directly orindirectly toward making this book a reality. First and foremost, we would like toexpress gratitude to Professor Norman F. Olson, who was instrumental in helpingus to initiate our first project on cheese rheology in 1989, when S.G. was a newassistant professor and M.M.A. was a graduate research assistant. Since then, withhis expert knowledge and friendly personality, Professor Olson has been a sourceof great support. Thanks are also due to Dr. Mark Johnson, Dr. Rusty Bishop, JohnJaeggi, and other past and current staff at the Wisconsin Center for Dairy Research.These people are invaluable resources for cheese research. This book draws frommuch of the research performed in S.G.s laboratory. As such, the efforts of manygraduate students and post-doctoral research associates are deeply appreciated. Theyinclude: Chyung Ay, James Colby, Kexiang Ding, Chang Hwang, Sun Young Kim,Sanghoon Ko, Gul Konuklar, Meng-I Kuo, Laura Marschoun, Kasiviswanathan Muth-ukumarappan, Hongxu Ni, Ramesh Subramanian, Salman Tariq, Deepa Venkatesan,Ya-Chun Wang, and Chenxu Yu. Thanks are also due to S.G.s colleagues, ProfessorsA. Jeffrey Giacomin and Daniel Klingenberg at the Rheology Research Center,University of Wisconsin-Madison, and Professor Karsten B. Qvist of KVL, Den-mark. Thanks to Hallie Kirschner for typing parts of the manuscript. The financialsupport of Wisconsin Milk Marketing Board and Dairy Management Inc. for manyof S.G.s projects is also deeply appreciated.

M.M.A. wishes to thank each member of his family for their full support andpatience during the writing of this book. He expresses appreciation to the following:Suat Yasa and Murat Yasa of Aromsa Limited Company, for their interest in the book;friends Elsie and Warren Sveum, Sarah and Alvaro Quinones, Mar Garcimartin-Akgul, and Arzu and Yann LeBellour for their constant encouragement; and formerstudents Filiz Lokumcu and Metin Yavuz for their valuable assistance in gatheringsome of the publications.

Sundaram GunasekaranM. Mehmet Ak


Table of Contents

Chapter 1 Cheesemaking An Overview

Cheese TypesCheesemaking

Milk PretreatmentCoagulationSyneresisShaping and SaltingRipeningProcess Cheese

References

Chapter 2 Fundamental Rheological MethodsDefinition of RheologyBasic Concepts

StrainStressStrain Rate

Fundamental MethodsUniaxial CompressionUniaxial TensionBending Test

Specimen with a Rectangular Cross-SectionSpecimen with a Circular Cross-Section

Torsion TestVane MethodStress-Relaxation Test

Analysis of Relaxation BehaviorCreep Test

Analysis of Creep BehaviorShear Rheometry

Sliding-Plates GeometryConcentric-Cylinders GeometryCone-and-Plate GeometryParallel-Plate GeometryCapillary Rheometry

Extensional RheometryLubricated Squeezing FlowEquations for Different Fluids in Lubricating Squeezing Flow

References


Chapter 3 Uniaxial Testing of Cheese

Uniaxial Compression MeasurementsStructure and Composition EffectsStress-Relaxation MeasurementsTorsion MeasurementsTension MeasurementsCreep MeasurementsBending MeasurementsVane MeasurementsShear MeasurementsLubricated Squeezing Flow MeasurementsReferences

Chapter 4 Fracture Properties of CheeseFracture MechanicsBrittle FractureGriffith CriterionDetermination of KIFracture Tests on Cheese

Notch TestsCutting, Slicing, and ShreddingCutting with Wire and BladeEye/Slit Formation and GrowthReferences

Chapter 5 Linear Viscoelasticity of CheeseMathematical Relations in Linear ViscoelasticityTypes of SAOS Measurements

Strain (or Stress) SweepFrequency SweepTemperature SweepTime Sweep

TimeTemperature SuperpositionApplication of SAOS in Cheese Rheology

Linear Viscoelastic Region of CheesesCheddar CheeseGouda CheeseMozzarella CheeseMozzarella: TimeTemperature Superposition ExampleFeta CheeseImitation CheeseQuarg CheeseProcessed Cheese

CoxMerz RuleReferences


Chapter 6 Nonlinear Viscoelasticity of Cheese

Pipkin DiagramSliding Plate RheometerLarge Amplitude Oscillatory Shear FlowSpectral AnalysisDiscrete Fourier TransformDetermining Material PropertiesAmplitude SpectrumStressShear Rate LoopsEffect of Wall SlipConstitutive Model for CheeseRelaxation Modulus Obtained from SAOSRelaxation Modulus Conforming to LAOSReferences

Chapter 7 Cheese TextureTexture Development in Cheese

Cheese Manufacturing Factors that Affect TextureTextural Changes during Storage

Measurement of TextureTexture Profile AnalysisTPA Testing of Cheese

Uniaxial Tests for Cheese Texture MeasurementCompression TestWedge Fracture Test

Torsion Test and Vane RheometryTexture Map

Dynamic TestsEmpirical Tests

CrumblinessCone PenetrometerStringiness

References

Chapter 8 Measuring Cheese Melt and Flow PropertiesMeltabilityEmpirical TestsObjective Tests

Steady Shear ViscometryCapillary RheometrySqueeze-Flow RheometryUW MeltmeterViscoelasticity Index for Cheese MeltabilityDynamic Shear RheometryHelical Viscometry


Cheese Melt Profile MeasurementUW Melt ProfilerDetermination of Melt Profile Parameters

Graphical MethodModeling Melt Profile

Constant Temperature TestTransient Temperature Test

Conduction HeatingReferences

Chapter 9 Measuring Cheese Stretchability

Empirical MethodsInstrumented MethodsVertical ElongationHorizontal ExtensionCompression TestsHelical ViscometryFiber-Spinning TechniqueThe Weissenberg EffectReferences

Chapter 10 Factors Affecting Functional Properties of Cheese

Properties of MilkCheesemaking Procedures

Addition of Starter Culture and CoagulantsCurd HandlingCooking, Stretching, and Cooling

Cheese CompositionMoisture ContentFat ContentSalt ContentpH

Post-Manufacturing ProcessesAging/RipeningFreezing and Frozen StorageHeat ProcessingOther Factors

References

Cheesemaking An Overview

Cheese is one of the first and most popular manufactured food products. Whatperhaps started out as an accidental curdling of milk has been further refined intocheesemaking. Over several thousand years, cheesemaking has advanced from anart to near science. Cheese varieties have proliferated to suit varied conditions andrequirements, especially during the last decade or so. It is estimated that more than2000 varieties exist (Olson, 1995), and the list may still be growing. Cheese is nowan important part of foods consumed in many countries (Table 1.1). In a recentsurvey, after spices, cheese was named the top ingredient that makes cooks feel morecreative (Doeff, 1994). Several cheeses satisfy varied requirements in order to beused as suitable ingredients in various dishes from baby foods to baked products(Table 1.2). Battistotti et al. (1984) described the history of cheese and cheesemakingin much detail. This chapter provides a broad overview of cheesemaking. For furtherdetails, readers are referred to many recent books on the subject (Scott et al., 1998;Spreer, 1998; Law, 1999; Walstra et al., 1999; Fox et al., 2000).

CHEESE TYPES

Todays wide array of cheeses may be classified according to the country of origin,manufacturing process, or some end-use property. Classifying cheeses based onmanufacturing and maturation processes by Olson (1979) produces a succinct list.A classification based on firmness and the maturation agent used produces a longerlist but may be more relevant if textural and rheological properties are important(Figure 1.1). A classification based on the distinctive manufacturing process involvedis also useful to understand the effect of the process on the cheese texture (Table 1.3).Other classifications of cheeses, e.g., according to milk source, overall appearance(color, size, shape), chemical analysis, etc., are also possible. Davis (1965) recog-nized the difficulty in classifying cheeses and attempted to group them based on thenature and extent of chemical breakdown during ripening or according to flavor.Such a classification is still not available. Fox (1993) proposed that the products ofproteolysis could be most useful for classification. One of the main difficulties whenusing classification schemes is that differences exist in the moisture range allowedwithin various categories published in the literature (Banks, 1998). Davis (1965)assigned some empirical texture/rheological parameter values to the terms from veryhard to soft (Table 1.4). The United States Code of Federal Regulations (CFR, 1998)stipulates certain standards of identity for cheeses classified according to theirconsistency, as listed in Table 1.5. The typical composition of milk and several cheesevarieties is given in Table 1.6. In the United States, the cheese market is dominated(almost equally) by Cheddar and Mozzarella cheeses. They comprise about two-thirds of the total cheese production over the past several years (Figure 1.2).

1


TABLE 1.1Consumption of Cheese in Selected Countries

Country

Consumption per Capita (kg)

1995 2000

a

North AmericaCanadaMexicoUnited States

10.861.47

12.26

10.761.61

13.75South America

ArgentinaBrazilVenezuela

10.352.823.48

11.062.722.76

Western EuropeDenmarkFranceGermanyIrelandItalyNetherlandsSpainSwedenSwitzerlandUnited Kingdom

16.8421.5111.905.54

18.6614.685.46

16.1414.288.75

16.2222.4912.506.70

20.3814.976.25

16.1214.319.88

Central EuropePoland 2.90 3.87

BalkansRomania 4.05 4.26

Eastern EuropeRussiaUkraine

2.031.26

1.410.79

North AfricaEgypt 5.27 5.83

Southern AsiaJapanSouth Korea

1.460.27

1.770.70

OceaniaAustraliaNew Zealand

8.258.17

11.108.48

a

Preliminary

Source:

After International Dairy Federation (www.dairyinfo.gc.ca/).


TABLE 1.2 Typical Requirements of Cheese as a Food Ingredient

Requirement Examples of Food ApplicationsExamples of Cheese or

Cheese-based Ingredient

Crumbles when rubbed Mixed saladsSoup

Feta, Cheshire, StiltonStilton

Sliceability Filled cheese rolls (finger foods)Sandwiches (filled, open, toasted)Cheese slices in burgersCheese slices on crackers

Swiss-type, Gouda, EdamSwiss-type, Cheddar, MozzarellaCheddarCheddar

Shreddability Consumer packs of sliced cheesePizza pie (frozen/fresh baked)Pasta dishes (lasagna, macaroni and cheese)

Swiss-type, Cheddar, MozzarellaMozzarella, Provolone, Cheddar, analog pizza cheese, Monterey

Cheddar, Romano, ProvoloneFlows freely when shaken Cheese sprinklings (on lasagna)

Snack coating (e.g., popcorn)Dry soup/sauce mixes

Grated Parmesan and RomanoCheese powdersCheese powders, enzyme-modified cheese

Flowability when blended with other raw materials

Fresh cheese desserts Quark, Fomage frias, Cream cheese

Ability to cream or to form a paste when sheared

CheesecakeTiramisuHomemade desserts

Cream cheese, RicottaMascarponeCream cheese

Nutritional value Baby foods Dried cheeses, esp. rennet-curd varieties (high in calcium)

Meltability upon grilling or baking

All cooked dishes (including sauces, fondues, pizza pie)

Mozzarella, Cheddar, Raclette,Swiss, Romano, analog pizza cheese, PCPs

a

Flowability upon grilling or baking

Most cooked dishes (e.g., pizza pie, cheese slices on burgers)

Chicken cordon-bleu

Mozzarella, Cheddar, Swiss, Romano, analog pizza cheese

PCPs, Cream cheeseFlow resistance upon deep-frying

Deep-fried breaded cheese sticksDeep-fried burgers with cheese inserts

Fried cheese dishes

PCPs, analog pizza cheese,custom-made

Mozzarella or string cheesePCPs, analog pizza cheesePaneer, acid-coagulated Queso Blanco

Stretchability when baked or grilled

Pizza pie Mozzarella, Kashkaval, young Cheddar, analog pizza cheese

Chewiness when baked or grilled

Pizza pie Halloumi, Mozzarella, Provolone,Kashkaval, young Cheddar

Limited oiling-off when baked or grilled

Pizza pie Mozzarella, Kashkaval

Limited browning when baked or grilled

Macaroni and cheeseLasagnaPizza pie

Cheddar, RomanoCheddar, Romano, ParmesanMozzarella, analog pizza cheese


CHEESEMAKING

Though there are numerous cheese varieties, the manufacturing processes of mostof them share several common steps. Variations at one or more steps during manu-facture produce cheeses of different textures and flavors. The essential steps incheesemaking and some variations for a few types of cheeses are schematicallyillustrated in Figure 1.3. These steps are as follows.

M

ILK

P

RETREATMENT

Milk used for cheesemaking is normally standardized and heat treated. In somecases, milk is homogenized. An acid-producing starter culture is then added.

The standardization of milk has become necessary to ensure that milk obtainedfrom several producers or dairies is of a standard composition and conditionthroughout the year. This is critical in cheesemaking because the legal standards ofvarious cheeses specify certain fat-to-protein ratios. The fat-to-protein ratio is deter-mined mainly by the fat-to-casein ratio in the milk (Fox et al., 2000) which can bemodified by removing fat or by adding cream or skim milk or skim milk powder,etc. It is also common to add color (annatto or carotene) and calcium (in the formof CaCl

2

) to the milk and to adjust milk pH to a desired level, known as preacidi-fication. Adding calcium speeds up coagulation or reduces the amount of rennetneeded and produces a firmer gel.

Heat treatment of milk is primarily intended to destroy the harmful microbialpopulation and enzymes in raw milk to assure product safety and quality. Pasteuri-zation is the most commonly used heat treatment (72C with 15 s holding time). It

Viscosity SoupsSaucesCheesecake

Cheese powders, PCPsCheese powders, Cheddar, Blue cheese, PCPs

Cream cheeseFlavor Most cheese dishes, soups

Baked productsSnack coatingsDressingsBaby foodReady-made meals

Cheddar, Romano, Swiss-type, Parmesan

Cheese powders, enzyme-modified cheese

Cheese powdersCheese powdersDried cheeseCheese powders

a

Pasteurized process cheese products.

Source:

After Fox et al., 2000. With permission.

TABLE 1.2 (continued)Typical Requirements of Cheese as a Food Ingredient

Requirement Examples of Food ApplicationsExamples of Cheese or

Cheese-based Ingredient


not only destroys most of the bacteria present, including lactic-acid bacteria, butalso inactivates many enzymes. A gentle heat treatment, known as thermization(60 to 65C with 15 to 30 s holding time) may also be used advantageously beforeor after pasteurization (Spreer, 1998). However, many cheeses are still producedfrom raw milk, especially in Europe (Fox et al., 2000). If the cheeses are made fromunpasteurized milk, they must be cured for at least 60 days at not less than 1.7C(35F), and the label should indicate the manufacturing date or state held for morethan 60 days. (NDC, 2000).

In traditional cheesemaking, the acid produced by microorganisms present inraw milk lowers the milk pH to a level sufficient for subsequent coagulation. How-ever, if the milk undergoes a heat treatment, selected cultures of lactic-acid bacteria

FIGURE 1.1

Natural cheeses classified according to the maturation agent used and firmness.(After Vedamuthu and Washam, 1983; Fox et al., 2000.)

TYPES OF NATURALCHEESESAcid Coagulated

Concentrated(from Whey)

Surface Ripened

Enzyme Coagulated

Mould RipenedInternal BacteriaRipened

Internal MouldSemi-soft

BlueDanablu

GorgonzolaRoquefort

HardStilton

Surface MouldSoftBrie

CamembertCoulommiersCarre de lEst

Very HardAsiagoGrana

ParmesanParmigiano

RomanoSabrinzSardo

SoftSalt-cured/

PickledDomiati

Feta

Semi-softCaerphilly

MahonMonterey Jack

Pasta filataMozzarellaProvolone

Caciocavallo

HardCaciocavallo

CheddarCheshire

ColbyGraviera

RasCheese with eyes

EdamEmmental (Swiss)

GoudaGruyere

MaasdamSamsoe

GjetostMyost

Primost

SoftCottageCreamQuark

Queso BlancoBakers

NeufchatelRicotta (Acid and heatcoagulated from whey)

Semi-softBrick

Bel PaeseHavarti

LimburgerMunster

OkaPort du Salut

St. PaulinTrappistTaleggioTilsiter

SoftLiderkranz


TABLE 1.3Classification of Cheeses by the Distinctive Manufacturing Process Involved

DistinctiveProcess Involved Characteristics Example Cheeses

Curd particles matted together Close texture, firm body CheddarCurd particles kept separate Slightly open texture Colby, Monterey JackBacteria-ripened throughout interior

Gas holes or eyes with eyeformation throughout cheese

Swiss (large eyes), Edam or Gouda (small eyes)

Prolonged curing period Granular texture; brittle body Parmesan, RomanoPasta filata Plastic curd; stringy texture Mozzarella, ProvoloneMold-ripened throughout interior

Visible veins of mold (blue-green or white); piquant, spicy flavor

Blue, Gorgonzola, Roquefort

Surface-ripened mainly by bacteria and yeasts

Surface growth; soft, smooth, waxy body; mild to robust flavor

Brick, Limburger

Surface-ripened mainly by mold Edible crust; soft, creamy interior; pungent flavor

Brie, Camembert

Curd coagulated mainly by acid Delicate soft curd Cottage, Cream, Neufchatel

Source:

After NDC, 2000. With permission.

TABLE 1.4Empirical Texture/Rheological Parameter Values Used in Cheese Classification

Cheese Type Moisture (%)

Logarithmic Scale Values

Viscosity Factor Elasticity Factor Springiness Factor

Very Hard < 25 > 9 > 6.3 > 2.3Hard 2536 89 5.86.3 22.3Semihard 3640 7.48 < 5.8 1.82Soft > 40 < 7.4 < 5.8 < 1.8

Source:

After Davis, 1965.

TABLE 1.5United States Federal Standards for the Maximum Moisture and Minimum Milk Fat for Classes of Cheese Designated by Consistency

ConsistencyMaximum moisture

content (%)Minimum milk fat

in solids (%)

Hard grating 34 32Hard 39 50Semisoft 50 (>39) 50Semisoft part skim 50 45 (

TABLE 1.6Typical Composition (% by Weight) of Milk and Some Cheese Varieties

Type and Cheese Moisture Protein TotalFat

TotalCarbohydrate

Fat in DryMatter Ash Calcium Phosphorus Salt pH

a

Milk

CowGoatSheepBuffalo

87.387.780.782.8

3.42.94.54.8

3.74.57.47.5

4.84.14.84.8

29.136.638.341.7

0.70.81.00.8

0.12

0.900.951.100.85

6.7

Acid Coagulated

Dry curd cottageCreamed cottageQuarkCreamNeufchatel

79.879.072.053.762.2

17.312.518.07.5

10.0

0.424.58.0

34.923.4

1.82.73.02.72.9

2.121.428.575.462.0

0.71.4

1.21.5

0.030.060.030.080.07

0.100.130.350.100.13

nil1.00

0.730.75

5.05.04.54.64.6

Heat-Acid Coagulated

ChhanaQueso Blanca, acidRicotta from 3%-fat milkRicotone from whey and milk

53.055.072.282.5

17.019.711.211.3

25.020.412.70.5

2.03.03.01.5

53.244.845.72.9

3.00

TABLE 1.6 (continued)Typical Composition (% by Weight) of Milk and Some Cheese Varieties

Type and Cheese Moisture Protein TotalFat

TotalCarbohydrate

Fat in DryMatter Ash Calcium Phosphorus Salt pH

a

Soft Ripened High Acid

CamembertFetaBlueGorgonzola

51.855.242.036.0

19.814.221.026.0

24.321.329.032.0

0.5

2.3

50.347.550.050.0

3.75.25.15.0

0.390.490.53

0.350.340.39

2.10

3.50

6.94.46.5

Semihard Washed

ColbyGoudaEdamFontinaHavarti-DanishMunster

40.041.541.442.843.541.8

25.025.025.024.224.723.4

31.027.427.825.526.530.0

2.02.21.4

1.1

51.746.947.644.646.951.6

3.43.94.23.32.83.7

0.680.700.73

0.72

0.460.550.54

0.47

0.650.820.961.202.201.80

5.35.85.75.65.96.2

Hard Cheese Low Temperature

CheddarManchego, SpainProvoloneMozzarella

36.737.940.954.1

24.928.125.619.4

33.126.926.621.6

1.3

2.12.2

52.445.245.147.1

3.93.64.72.6

0.72

0.760.52

0.51

0.500.37

1.801.502.201.00

5.55.85.45.3

Hard Cheese High Temperature

ParmesanRomanoSwissKaflatyri, Greece

29.230.937.234.2

35.731.828.424.8

25.826.927.428.3

3.23.63.4

36.539.043.7

6.06.73.54.7

1.181.060.96

0.690.760.60

3.003.001.20

5.45.45.65.2

a

pH at time of retailing.

Source:

After Hill, 1995; Fox et al., 2000.


must be added. The type of bacteria added depends on the cheese type and cheese-making protocol used. These bacteria break down the milk sugar, lactose. Lacticacid produced during this process lowers the pH. An alternative to adding starterculture is to acidify the milk directly by adding lactic acid or hydrochloric acid orgluconic acid-

-lactone, an acidogen. Though this direct acidification allows bettercontrol, starter culture remains active in the cheese during ripening, months aftercheese manufacture, and contributes to cheese flavor. Therefore, direct acidificationis used primarily when manufacturing cheese varieties for which texture is moreimportant than flavor, e.g., cottage cheese, quark, Mozzarella, etc. (Fox et al., 2000).

Walstra and Jenness (1984) reported an increase in cheese yield when usingpasteurized milk. This is due to caseinwhey protein interaction and greater moistureretention. One disadvantage of pasteurization, however, is that aged cheeses developtheir flavors more slowly and to a lesser extent than cheeses made with raw milk(Kristoffersen, 1985). This has led many cheesemakers to use milk heated to 60 to68.5C for 15 s or less instead of pasteurized milk (Johnson, 1998).

C

OAGULATION

Since pretreating milk is a fairly recent practice relative to the history of cheese-making, many consider coagulation as the first and most important step in cheese-making. Coagulation is the step during which milk undergoes a profound physicaland rheological change, that is gelation. Milk gel is formed by aggregation of milkprotein, the caseins. This can be accomplished by:

1. The action of a proteolytic enzyme2. Lowering the pH below the isoelectric point of protein (~ 4.6)3. Heating to about 90C at a pH of about 5.2 (i.e., higher than the isoelectric point)

FIGURE 1.2

United States total (excludes cottage cheese) and Cheddar and Mozzarellacheese production trends. (After Annual Summary of Dairy Market Statistics of years 1997through 2001. Agricultural Marketing Service, USDA. Mozzarella data from University ofWisconsin Dairy Marketing Web site: www.aae.wisc.edu/future.)


Among these, enzymatic coagulation is the most popular. Acid coagulation viafood-grade acidulants is used to manufacture quark, cottage, and cream cheeses.Heat coagulation is used for Ricotta and Queso Blanco cheeses (Johnson and Law,1999; Fox et al., 2000).

Enzymatic coagulation is accomplished by enzymes from animal (e.g., calfrennet, porcine pepsin), plant (e.g., Cynara Cardunculus from Cardom, Circium and

FIGURE 1.3

Major steps in cheesemaking (actual steps and/or conditions for a particularcheese may vary). (After Scott et al., 1998; Fox et al., 2000.)

Pasta Filata Cheese(e.g., Mozzarella)

Pretreatment(Standardization, Homogenization, Heat treatment, Starter addition)

Coagulation(Rennet /Coagulant addition)

Syneresis(Cutting, Stirring, Scalding/cooking, Whey removal)

Milk

Hard Cheese(e.g., Cheddar)

Soft Cheese(e.g., Camembert)

Semi Hard Cheese(e.g., Gouda)

Moulding

Brining

Storage

Turning

Packing

Hot waterWashing

Pressing &Moulding

Brine Salting

Waxing &Wrapping

Cheddaring

Milling

Dry Salting

Ripening

Heating &Stretching

Moulding

Brine Salting


Carlina Spp. from thistle), or microbial (e.g.,

Endothia parasitica

,

Rhizomucor miehei

)origin. Enzymatic coagulation consists of two phases. During the first or primaryphase, the hydrophilic hairy structure, stabilized by steric hindrance, of

-casein iscleaved off at Phe105-Met106 bond. The secondary or clotting phase is initiated as85 to 90% of the

-casein is cleaved and results in the aggregation of the alteredprotein micelles. The

-casein loses its ability to stabilize the remainder of thecaseinate complex. The result is soluble glycomacropeptides (residues 106169),and hydrophobic, para-

-casein (residues 1105). As the protein micelles continueto aggregate, a loose network forms, entrapping fat globules, water, and water-solublematerials. The para-

-casein left on the micelle is still connected to

- and

-casein,but it is highly hydrophobic and basic, leading to destabilization of the micelle.

Gel formation by association of the modified micelles in the secondary phaseis highly dependent on the milks temperature and calcium content. The coagulationrate is also highly dependent on the concentration and activity of the enzyme solution.Increases in both of these factors shorten coagulation time and increase firmness.Although it is not clear how the micelles aggregate, there are two hypotheses. Oneis that hydrophobic bonding occurs between the para-

-casein. The other is thatcalcium and calcium phosphate bonding occurs in

- and

-caseins.Other factors that affect aggregation are casein concentration and milk pH. The

aggregation rate is proportional to the square of casein concentration (Lomholt and Qvist,1999). As discussed previously, the effect of renneting action strongly depends on milkpH. Each milk-clotting enzyme has an optimum pH at which it is most active. Extremesin acid or base also denature the enzymes but not as irreversibly as high temperatures.Lowering the pH leads to a decrease in coagulation time mainly due to increasedenzyme activity, but rate of aggregation is also affected (Lomholt and Qvist, 1999).

The aggregation of casein micelles forms strands of casein particles of aboutthree particles wide and 10 particles long, alternated by some thicker nodes ofparticles (Walstra et al., 1999). After this, the aggregates grow more compact (Baueret al., 1995). The time when aggregates become visible is known as the flocculationtime or rennet coagulation time (RCT). When the flocs grow to occupy the entirevolume, the gel is said to have been formed. The gel network is very irregular, withmany pores several micrometers in width (Walstra et al., 1999). Aggregation ofcasein micelles into chains, then into strands and clusters, and eventually into anamorphous mass has been observed by microscopic evaluation in both acid- andenzyme-coagulated systems (Kimber et al., 1974; Glaser et al., 1980).

From a rheological standpoint, casein aggregation and gel formation representan increase in viscosity and gel modulus, respectively. The viscosity increase inrenneted milk, however, is observed after an initial lag time (~ 60% RCT) duringwhich the viscosity may actually decrease slightly due to a decrease in voluminosityof the casein micelles following the release of macropeptides (Fox et al., 2000). Afterthis, the viscosity increases exponentially up to the onset of gelation (i.e., 100% RCT).The viscosity increase and the concomitant change in physical properties have beenused to identify the RCT (Kopelman and Cogan, 1976; Ay and Gunasekaran, 1994;Fox and McSweeney, 1998; Konuklar and Gunasekaran, 2002).

The modulus of the gel increases markedly at gelation time. In fact, gelationtime is defined as the time at which the gel modulus increases rapidly. The initial


increase in modulus is due to the increase in number of contacts between micelles.Subsequently, the strengthening of intermicellar bonds translates into increased gelmodulus (Walstra et al., 1999). It has been premised that the increase in gel firmnessis due to the increase in the number of bonds with time (Lomholt and Qvist, 1999).This premise was based on the observation that, though the modulus continues toincrease, the phase angle stays relatively constant, i.e., the nature of the bonds doesnot change (Dejmek, 1987; Lopez et al., 1998). Figure 1.4 shows a typical plotdepicting changes in viscoelastic moduli and the phase angle of the coagulating milkgel system. As more micelles aggregate, they may fuse together and strengthen thebonds (Lomholt and Qvist, 1999). The modulus continues to increase for severalhours after gelation time, signifying gel firming. The microstructure of the gel hasbeen observed to become coarser with larger pores and thicker strands (Lomholtand Qvist, 1999). Carlson et al. (1987) presented a detailed analysis of all aspectsof milk coagulation kinetics in a four-part series of papers.

S

YNERESIS

Due to its porous nature, the coagulum has the propensity to contract and expelentrapped liquid. This is known as syneresis, an important step in concentratingthe milk. To a great extent, the success of the remaining cheesemaking steps dependson satisfactorily draining the whey. Also, most of the lactose, a substrate forpostproduction microbial activity, is lost in the whey, which helps to prevent some

FIGURE 1.4

Changes in storage (G

) and loss (G

) moduli and phase angle (

) of therennetted milk during coagulation. The gel point is identified at G

G

crossover which occursat

= 45. (After Uludogan, 1999.)

104

103

102

101

100

101

102

G, G

(P

a)

350030002500200015001000500Time (s)

80

70

60

50

40

30

20

()gel point

G G


adverse effects (Scott et al., 1998). In an undisturbed gel, however, syneresis occursvery slowly. Therefore, during cheesemaking, syneresis is accelerated by cuttingthe coagulum into small cubes, which increases the surface area and reduces thedistance for the diffusion process to facilitate whey removal. Syneresis can also beenhanced by decreasing the pH or increasing the temperature of the coagulum(Walstra et al., 1999).

Cutting the coagulum to facilitate faster whey removal must be timed precisely.If the coagulum is cut too soon, some milk solids leave the curd along with whey.Whey normally carries water-soluble components including lactose, whey proteins,salts, peptides, and other nonprotein nitrogenous substances (Scott et al., 1998). If itis cut too late, more water gets trapped in the matrix, resulting in high-moisturecheese. Therefore, cheesemakers have been striving for many years to identify thecorrect curd-cutting time. Since the coagulum firmness continues to increaseuneventfully over several hours, it is hard to determine an optimal curd-cutting time.Many instrumented and so-called objective curd-cutting-time predictions have beenmade (Hori, 1985; Payne et al., 1993; Gunasekaran and Ay, 1996; OCallahan et al.,1999). Some commercial units are available based on some of these techniques (Foxand McSweeney, 1998; OCallahan et al., 1999). However, there is still no universalprocedure to identify optimal curd-cutting time. Most large factories apply a set timeschedule, depending on the cheese type, to cut the curd after adding the rennet. Inmany smaller cheesemaking facilities, cutting time is still determined by the sub-jective judgment of the cheesemaker. Recently, Konuklar and Gunasekaran (2002)reported a novel rheological technique for identifying the curd-cutting time. Theyobserved that the viscosity versus time curves during coagulation under continuoussteady shear exhibit several abrupt peaks. The first peak over 40 kPa.s coincideswith cutting time determined by an experienced cheesemaker during Cheddar, Swiss,and Gouda cheesemaking (Figure 1.5.)

Syneresis is the process that a cheesemaker can use to closely control themoisture content of the cheese and hence the microbial and enzymatic activity inthe cheese, which affects ripening, stability, and quality of the cheese (Fox et al., 2000).Therefore, it is specific to a particular cheese type or cheese family. Walstra et al.(1999) listed the following factors as affecting syneresis: firmness of gel at cutting;surface area of the curd; any applied pressure; acidity; temperature; composition ofthe milk; and other variables. Pearse and Mackinlay (1989) discussed the mechanismand biochemical aspects of syneresis.

Stirring exerts pressure, causing curd particles to collide, and facilitates theircompression for a short time. Stirring also keeps the curd from settling in the vat.For Cheddar- and Swiss-type cheeses, the cut coagulum is not stirred immediatelyafter cutting. The curdwhey mixture is cooked (at about 40C for Cheddar-typeand 50C for Swiss-type) and vigorously agitated during cooking. For soft cheeses,the curd is ladled and hooped which allows whey to drain without stirring. Cookingthe curd, also known as scalding, enhances syneresis by facilitating contraction ofthe protein matrix. Heating further enhances acid production by the starter organisms.Lowering pH, combined with increased temperature, not only helps to expel morewhey but also affects the dissolution of calcium phosphate, and thus has majorimplications for characteristics of the cheese (Johnson and Law, 1999). The scalding


step can be used to distinguish four major groups of cheese excluding soft cheeses,some of which may be scalded (Scott et al., 1998):

1. Textured cheeses such as Cheddar or Cheshire2. Pasta filata types or kneaded cheeses3. Cheeses untextured in the vat (e.g., Edam and Gouda) and those which

acquire texture later (e.g., Tilsiter and Emmental)4. Blue-veined cheeses

FIGURE 1.5

Viscosity (

) of coagulating milk system vs. time after rennetting measuredunder a continuous steady shear stress of 0.2 Pa. The first viscosity peak over 40 kPa.scoincided with the cutting point (CTP) determined manually during (a) Cheddar; (b) Swiss;and (c) Gouda cheesemaking. (After Konuklar and Gunasekaran, 2002. With permission.)


To manufacture some cheeses (e.g., Edam, Gouda, or Havarti), the curd is washedby adding water to the curdwhey mixture. This accomplishes two things:

1. It adjusts the pH of the cheese independently of its moisture content byremoving lactose and other solubles from the curd.

2. It enhances whey removal by adding hot water to raise the curd tempera-ture, as is the case during direct heating.

It should be noted that using hot water to stretch pasta filata cheeses (e.g.,Mozzarella, Provolone, etc.) is not considered as washing (Scott et al., 1998).

S

HAPING

AND

S

ALTING

When the curd is at the desired moisture content and pH, it is separated from thewhey. The curd particles are subsequently shaped into some form and salted(primarily by NaCl), not necessarily in that order. These steps, though common formost cheeses, are performed very differently, depending on the cheese type. AsJohnson and Law (1999) stated, the manner in which cheese curd and whey areseparated can affect texture as well as color and flavor.

When manufacturing hard cheeses such as Cheddar, the curdwhey slurry ispumped into a vat with a perforated bottom for whey removal. The curd is cheddaredfor about 90 min. Cheddaring is the process in which curd particles are allowed tofuse or mat together. The mats are then cut into slabs and stacked on top of eachother. Physical properties and pH of the curd at this stage affect curd fusion andappearance of the finished cheese (Olson, 1995). When the desired pH has beenreached, the slabs are milled into small pieces. At this stage, the curd may be sprayedwith warm water and stirred for further whey removal. Salt is sprinkled on at a levelof about 2 to 3% which expels additional whey. The salted curd is then hooped inmolds and pressed overnight.

Manufacturing steps for Mozzarella and other pasta filata cheeses differ mark-edly after the milling stage described above. The milled curd is kneaded, i.e.,heated and stretched in warm water (about 60 to 70C) using an open-channel,single-screw or twin-screw extruder/auger. This transforms the curd into a cohe-sive, viscoelastic mass. Due to the conveying action of the auger, the curd massgets stretched into a continuous stream of molten material. This stretching step isunique to Mozzarella manufacturing. It imparts the characteristic oriented micro-structure and related textural attributes of these cheeses (Oberg et al., 1993; Akand Gunasekaran, 1997). The molten cheese is then placed into molds and cooled.When the cheese is cool enough to keep its shape, the mold is removed and thecheese is salted by dropping it in a nearly saturated brine solution (about 25%salt) at 1 to 4C. The cold brine temperature cools the cheese further. In fact,much of the total cooling of Mozzarella occurs during brining (Nilson, 1968).Brine salting is a slow process, taking several days for uniform salt distributionwithin a cheese block. It should be noted that, concomitant with salt intake, thecheese loses moisture. The salt and moisture gradients in a cheese during saltingare opposite of each other (Turhan and Gunasekaran, 1998; Walstra et al., 1999;


Fox et al., 2000). Though brine salting is the traditional method, salting of Moz-zarella can also be done by adding salt directly to the curd just before stretching,during stretching, or between stretching and molding. This direct salting reducesthe subsequent brining time.

Another major variation is surface salting. Salt is rubbed directly on the cheesesurface (e.g., Romano and Gorgonzola). This is repeated for several days so the saltdiffuses throughout. In many other cheeses, surface salting and brining are used incombination (e.g., Gruyere and Emmental).

Regardless of the method used, salting is a vital step in cheesemaking becauseunsalted cheese is virtually tasteless (Olson, 1995). Salt also plays a major role inthe texture, flavor, and microbial quality of cheese (Kindstedt et al., 1992; Paulsonet al., 1998; Fox et al., 2000). Salt inhibits the growth of certain bacteria, whichare harmful to the cheese and cause spoilage, especially on the surface. It furtherassists in dissolving the casein and in rind formation, as well as in slowing downenzyme activity. Salt concentration in cheese varies greatly from less than 1% inEmmental to 7 to 8% in Domiati (Fox and McSweeney, 1998). The salt contentmay also vary considerably within a cheese block due to the slow diffusion of salt.Thus, there is more water and less salt at the center of a cheese block comparedto at the surface (Prentice, 1993). This unevenness in the salt (and water) distributionalso leads to variation in the rheological properties of the cheese within the block(Visser, 1991).

As already noted, hard and semihard cheeses are shaped by applying externalpressure. Pressing expels whey and facilitates faster curd fusion into an integral massof a desired shape with a rind. Though simple enough, pressing is perhaps the leastunderstood step in cheesemaking (Scott et al., 1998). The time, pressure, and effi-ciency of pressing are related to the condition of the curd at pressing time and thedecrease in pH during pressing (Johnson and Law, 1999). Sometimes pressing isdone in conjunction with vacuum to force out any entrapped air.

The complex nature of the interrelationships among many of the cheesemakingparameters makes controlling cheese properties very hard. Tables 1.7a to 1.7d presenthow various cheesemaking and technological factors affect cheese quality. This setof four tables was prepared in 1961 for the Danish Samso cheese (Birkkjaer et al.,1961), but the information it contained is generally valid for other hard/semihardcheeses (e.g., Gouda).

R

IPENING

Ripening is the natural process of microbial and biochemical reactions that occursin a cheese after its manufacture and during storage. Ripening gives different cheesestheir unique flavors, textures, and appearances. Except for some soft cheeses (e.g.,cottage cheese, cream cheese, quark, etc.), almost all cheeses are held under con-trolled conditions to develop distinct attributes. Ripening essentially results from theaction of microorganisms present within the curd mass and on its surface. Ripeningis also influenced by residual enzymes present in the cheese curd. Cheeses areripened over a range of time from several days (e.g., Mozzarella) to more than ayear (e.g., Cheddar).


Fox et al. (2000) list the following ripening agents in cheese:1. Coagulant chymosin or other suitable proteinase2. Milk some indigenous enzymes contained in milk, e.g., plasmin3. Starter culture host of enzymes released upon cell death and lysis4. Secondary microflora microflora that perform some specific secondary

function (e.g., propionic acid, bacteria, and yeasts and molds)5. Exogenous enzymes proteinases, peptidases, and lipases added by

cheesemakers to accelerate ripening

TABLE 1.7A Effect of Cheesemaking Parameters on Cheese Quality (Prepared forDanish Samso Cheese, a Gouda-Type Semihard Cheese) Modifications Needed to Produce a Harder Cheese and Their Primary and Secondary Effects

Factor No. Efficiency

a

Modifications Primary Effect Secondary Effect

b

1 Use fresh milk or pasteurize at approx. 70C (158F)

Slightly improves whey expulsion

Cheese becomes slightly less acid. Ca content increases slightly

2 + Reduce or omit addition of water to the milk

Improves whey expulsion

Cheese becomes more acidic. Ca content increases

3

c

+ Add CaCl

2

to the milk

Improves whey expulsion Ca content increases. Adding more than40 g/100 kg milk (0.68 oz/110 lbs milk)may give an off flavor

4 + Increase amount of culture/starter or prolong pre-ripening period of the milk

Slightly improves whey expulsion from the curd

Cheese becomes more acidic. Ca content decreases. Too much culture/starter or too long a preripening makes cheese sour, short, and flaky

5

c

(+) Lower renneting temperature

At the same cooking temperature, whey drain in the vat increases slightly due to a greater rise in temperature. If no cooking occurs, whey is reduced, and cheese becomes softer

A renneting temperaturethat is too low results in weak curd and thus a bigger loss in the whey.Ca content decreases

6

c

+ Cut curd into smaller cubes

Improves whey expulsion Very fine cutting may result in a bigger loss in whey. Many of the grains may retain some of the whey during molding/pressing, so cheese may be softer


8 + Reduce or omit addition of water during cooking

Improves whey expulsion of curd, esp. by reducing relatively large additions of water

Cheese becomes sour and may eventually become too firm in the curd and thus will often break.Ca content increases

9 +++ Increase cooking temperature

Increases whey expulsion in the vat

Cheese becomes less acidic and tougher At high temperatures, esp. above 40C (105F); cheese may develop an off flavor

10 +++ Avoid a temperature drop during final stirring

Increases whey expulsion in the vat and during pressing

Cheese becomes less acidic. Ca content increases

12 ++ Reduce or omit salt addition to whey during final stirring

Cheese grains swell less and thus retain less whey

Cheese becomes less acidic. Ca content increases. Brine salting may be prolonged to get adequate salt content

13

c

+++++

d

Leave cheese at cooking temperature in water or whey after pressing in the vat

Cheese liberates a relatively large quantity of whey before rind is closed

Ca content decreases considerably

14 ++ Increase temperature in pressing room

Increases amount of whey draining during pressing

Cheese becomes slightly less acidic. If it is not cooled longer, the risk of cracked rind and gas from coliforms may increase

15

c

+ Prolong pressing time (possibly until the next morning)

Increases amount of whey draining during pressing

You might see adhesion, especially when using cotton cloths and a relatively high pressing temperature. Counteract this by using nylon cloths and cooling during last part of pressing

a

+ Represents relative efficiency, the higher the better. (+) means that the effect depends on other conditions.

b

Shaded effects reduce acidity; bold-faced effects increase acidity.

c

Factor numbers 3, 5, 6, 13, and 15 show modifications that influence either acidity or firmness but notboth. All other factors influence both.

d

An extraordinary change in technique, 3 hours at 38C.

Source:

After Birkkjaer et al., 1961. With permission.

TABLE 1.7A (continued)Effect of Cheesemaking Parameters on Cheese Quality (Prepared forDanish Samso Cheese, a Gouda-Type Semihard Cheese) Modifications Needed to Produce a Harder Cheese and Their Primary and Secondary Effects


a


b


TABLE 1.7B Effect of Cheesemaking Parameters on Cheese Quality (Prepared forDanish Samso Cheese, a Gouda-Type Semihard Cheese) Modifications Needed to Produce a Softer Cheese and Their Primary and Secondary Effects


a


b

1 Pasteurize at 65C (150F) or above 75C (166F), esp. above 80C (175F)

Slightly reduces whey expulsion (above 80C [175F] somewhat)

Cheese becomes (above 80C [175F] somewhat) more acidic. Ca content decreases. High pasteurization temperatures often lead to weak eye formation

2 + Add water to the milk

Reduces whey expulsion Cheese becomes less acidic. Ca content increases

3

c

+ Reduce or omit addition of CaCl

2

to the milk

Reduces whey expulsion Ca content decreases

4 + Reduce amount of culture/starter or shorten or omit preripening period of the milk

Slightly reduces whey expulsion

Cheese becomes less acidic. Ca content decreases. Not enough culture/starter or a pre-ripening that is too short may produce a tough cheese with an off flavor

5

c

(+) Raise renneting temperature

At the same cooking temperature, whey expulsion in the vat is slightly reduced due to a smaller rise in temperature. If no cooking occurs, whey expulsion increases and cheese is firmer

A renneting temperature that is too high will cause cutting problems since the coagulum will be too firm during cutting. Ca content increases slightly

6

c

+ Cut curd into bigger cubes

Reduces whey expulsion Big curd cubes can be easily stirred into smaller pieces, causing greater whey drain than intended and greater loss in the whey. Many grains may retain some whey when cheese is molded so cheese becomes softer than intended

8 + Add more water during cooking

Reduces whey expulsion, esp. when relatively large amounts of water are added

Cheese becomes less acidic. Ca content decreases. If you add more than 20% of the quantity of milk, cheese often develops an off flavor


9 +++ Lower cooking temperature

Reduces whey expulsion Cheese becomes more acidic. Cheese which is already acidic may crack easily

10 +++ Cool curd cubes for about 15 min before final stirring ends

Reduces whey expulsion in the vat and during pressing

Cooling without water leads to acidic cheese. Cooling with water leads to small or no change in acidity, depending on amount of water. Ca content decreases

12 ++ Add more salt to whey during final stirring

Curd cubes swell more and retain more whey

Cheese becomes more acidic. Ca content decreases. Shorten brine salting so cheese is not too salty. Heavy salting in the vat may restrain fermentation, producing cheese with high pH

13c +++++d Reduce pressing temperature or drain the whey faster

Rind closes earlier, slowing whey expulsion

Ca content increases

14 ++ Lower temperature in pressing room

Reduces whey expulsion during pressing

Moderate cooling yields more acidic cheese. Cooling too soon retards fermenting and gives high pH cheese. Cooling after or during last part of pressing, if long enough, slows rind cracking and coliform production

15c + Use low pressure to start or shorten pressing time

Less whey is pressed out of the cheese

Low pressure and short pressing time may causebad rind closing, fermenting in rind (cracked rind) and open texture

a + Represents relative efficiency, the higher the better. (+) means that the effect depends on other conditions.b Shaded effects reduce acidity; bold-faced effects increase acidity. Shaded and bold-faced effects may resultin more or less acidity.c Factor numbers 3, 5, 6, 13, and 15 show modifications that influence either acidity or firmness but notboth. All other factors influence both.d An extraordinary change in technique, three hours at 38C.

Source: After Birkkjaer et al., 1961. With permission.

TABLE 1.7B (continued)Effect of Cheesemaking Parameters on Cheese Quality (Prepared forDanish Samso Cheese, a Gouda-Type Semihard Cheese) Modifications Needed to Produce a Softer Cheese and Their Primary and Secondary Effects

Factor No. Efficiencya Modifications Primary Effect Secondary Effectb


TABLE 1.7C Effect of Cheesemaking Parameters on Cheese Quality (Prepared forDanish Samso Cheese, a Gouda-Type Semihard Cheese) Modifications Needed to Produce a Less Acidic Cheese and Their Primary and Secondary Effects


1 + Use raw milk or pasteurize at approx. 70C (158F)

Slightly improves whey expulsion

Cheese becomes slightly firmer. Ca content increases slightly

2 ++ Add water to the milk Reduces whey expulsion Cheese becomes softer. Ca content decreases

4 ++ Reduce amount of culture/starter, or shorten preripening period of the milk

Less acidification Cheese becomes a little softer. Ca content increases. Not enough culture/starter and a weak preripening produces a tough cheese with an off flavor

7c ++ Start cooking earlier by shortening prestirring or intermediate stirring, and prolong final stirring correspondingly

Development of lactic-acid bacteria is restrained and whey is expelled

Ca content increases

8 +++ Add more water during cooking

Greater diffusion of sugar and Ca from curd cubes to the whey

Adding more than 20% water may produce a cheese with an off flavor. Increasing the water added produces cheese with a higher water content and lower Ca content

9 ++++++ Raise cooking temperature

Development of lactic-acid bacteria in the vat is slowed. Whey is expelled earlier

Cheese becomes firmerand tougher. At high temperatures, especially above 40C (105F), cheese develops an off flavor

10 ++ Avoid a drop in temperature during final stirring

Development of lactic-acid bacteria is slowed

Cheese becomes firmer. Ca content increases

11c + Prolong the time for final stirring so total stirring time is longer

Acidity is slightly changed because development of lactic-acid bacteria is slowed. But because curd cubes are kept in the whey longer, more Ca is discharged

Cheese consistency becomes more supple (flexible), so cheese is easier to cut


Various methods of influencing cheese ripening are summarized in Table 1.8.The primary factors in this process are (Scott et al., 1998):

1. Storage temperature and humidity, humidity being less important forcheeses hermetically packed (e.g., with a wax coating).

2. Chemical composition of the curd fat content, level of amino acids,fatty acids, and other by-products of enzymatic action.

3. Residual microflora of the curd primarily from the starter culture. Thecheesemaker can do little to influence it except in the case of blue-veinedor surface-ripened cheeses.

Temperature and humidity are factors that cheesemakers can control duringripening. In general, higher temperatures increase the microbial growth rate andother biochemical reactions occurring in the curd. Thus, cheeses matured at differenttemperatures can have different flavor profiles. Accordingly, proper control of storagetemperature is essential. Variety-specific storage temperature control protocols have

12 Reduce or omit addition of salt to whey during final stirring

Curd cubes swell less and thus retain less whey

Cheese becomes firmer. Ca content increases. Brine salting should be prolonged to get an adequate salt content

14 + Cool cheese early, or carry through pressing at high temperature 40C (105F)

Development of lactic-acid bacteria is slowed

Cooling results in a softer cheese. Cooling too early may result in high pH cheese. High pressing temperature makes a firmer cheese, and the danger of a cracked rind and fermentation is increased if it is not cooled after pressing

a + Represents relative efficiency, the higher the better.b Shaded effects result in softer cheese; bold-faced effects result in firmer cheese. Shaded and bold-facedeffects may result in softer or firmer cheese.c Factor numbers 7 and 11 show modifications that influence either acidity or firmness but not both. Allother factors influence both.


TABLE 1.7C (continued)Effect of Cheesemaking Parameters on Cheese Quality (Prepared forDanish Samso Cheese, a Gouda-Type Semihard Cheese) Modifications Needed to Produce a Less Acidic Cheese and Their Primary and Secondary Effects



TABLE 1.7D Effect of Cheesemaking Parameters on Cheese Quality (Prepared forDanish Samso Cheese, a Gouda-Type Semihard Cheese) Modifications Needed to Produce a More Acidic Cheese and Their Primary and Secondary Effects


1 + Pasteurize at 65C (150F) or above 75C (166F), esp. above 80C (175F)

Slightly reduces whey expulsion (above 80C [175F] somewhat)

Cheese becomes slightly softer (above 80C [175F] somewhat). Ca content decreases slightly

2 ++ Reduce or omit addition of water to the milk

Improves whey expulsion from the curd

Cheese becomes a little firmer. Ca content increases

4 ++ Increase amount of culture/starter or prolong preripening of the milk

Increases acid production Cheese becomes a little firmer. Ca content decreases. Too much culture/starter and too strong preripening causes cheese to be sour, short, and flaky

7c ++ Cook longer by prolonging prestirring or intermediate stirring, and shorten final stirring correspondingly

Lactic-acid bacteria have better growth conditions in the vat. Whey expulsion occurs later

Ca content decreases. A long intermediate stirring time increases the loss in the whey because curd is easily stirred into pieces

8 +++ Reduce or omit addition of water during cooking

Less diffusion of sugar and Ca from curd cubes to the whey

Cheese retains more Ca and less water. It may become too acidic and stiff and break. Cheese becomes softer. Cheese which is already acidic may crack

9 ++++++ Lower cooking temperature

Lactic-acid bacteria have better growth conditions in the vat. Whey expulsion occurs later

Cheese becomes softer.Ca content decreases

10 ++ Cool curd cubes for about 15 min before end of stirring. A small amount of water is optional

Lactic-acid bacteria have better growth conditions

A short stirring time produces a tough cheese. Cut surface often gets horny and greasy after storage

11c + Shorten the time of final stirring so total stirring time is shorter

Acidity is changed slightly because development of lactic-acid bacteria is improved. But because curd cubes are kept in the whey for a shorter time, less Ca is discharged

Cheese becomes softer.Ca content decreases. Brine salting should be shortened so cheese is not too salty


been developed to optimize cheese quality. For example, Swiss-type Emmental isheld at a low temperature initially (10 to 15C) to facilitate the growth of lactic-acidbacteria. Later, the temperature is increased (20 to 24C) so that propionic bacteriacan grow. These are essential for the characteristic Emmental flavor and eyes. Forblue-veined cheeses (e.g., Gorgonzola, Roquefort, Stilton), warm-temperature stor-age is followed by low-temperature storage (Scott et al., 1998). Prevailing relativehumidity during storage (80 to 85%) helps to control the moisture content of cheesesnot covered with moisture barriers such as a wax coating. The moisture equilibriumin the cheese changes due to reactions occurring that require or release water.Increase in moisture content during storage affects the solute concentration andmicrobial growth rate. In general, higher moisture content promotes more vigorousgrowth of microorganisms than does lower moisture content. In addition to tempera-ture and moisture, other factors such as curd pH, inhibitory substances (e.g.,antibodies and salts), and oxidationreduction potential affect the microbial popu-lation in the cheese (Scott et al., 1998; Fox et al., 2000). The enzymes relevant formaturation in most hard cheeses are active in the pH range of 4.9 to 5.5, and in softcheeses from pH 5.3 to 6.0 (Scott et al., 1998).

Protein, fat, and lactose are hydrolyzed (i.e., proteolysis, lypolysis, and glycoly-sis, respectively) to varying extents during cheese ripening. Among these, proteolysisof casein is the most important. Proteolysis of - and -casein occurs due to any

12 Increase amount of salt added to the whey during final stirring

Curd cubes swell more and thus retain more whey

Too heavy salting in the vat restrains acidification, which may produce a high-pH cheese

14 + Take care that cheese temperature during pressing stays near the optimum temperature of the bacteria

Lactic-acid bacteria have better growth conditions during pressing. Pressing at high temperatures, or cooling too early to low temperatures in the curd, restrains acidification

Since rind fermentation can be prevented rather effectively by cooling, cheese should be cooled after pressing or during the last part of pressing,if this is long enough

a + Represents relative efficiency, the higher the better.b Shaded effects result in softer cheese; bold-faced effects result in firmer cheese.c Factor numbers 7 and 11 show modifications that influence either acidity or firmness but not both. All otherfactors influence both.


TABLE 1.7D (continued)Effect of Cheesemaking Parameters on Cheese Quality (Prepared forDanish Samso Cheese, a Gouda-Type Semihard Cheese) Modifications Needed to Produce a More Acidic Cheese and Their Primary and Secondary Effects



residual rennet from what was added for coagulation, natural proteases, and proteasesand polypeptidases from starter or adventitious bacteria (Scott et al., 1998). This isessential for cheese flavor development. Fat contains lipophilic flavor compounds,which develop or are released by microbial or enzymatic action through oxidation,decarboxylation, and eventually reduction of decarboxyl compounds. Glycolysis isalso initiated by adding a starter culture and reaches its peak in the milk during thepreripening stage. Here lactic acid, acetic acid, and CO2 are produced. In somecheeses, citrate is also metabolized into citric acid.

Proteolysis is also mainly responsible for changes in the body and texture ofcheeses. The breakdown of proteins first involves the conversion of casein fractionsinto large peptides. These peptides are later broken down to lower molecularweight products. The primary proteolysis in ripening has been defined as thechanges in caseins, which can be detected by polyacrylamide gel electrophoresis.The products of secondary proteolysis include the peptides and amino acids thatare soluble in the aqueous phase of the cheese. In mature Cheddar, approximatelyone-third of the protein has been broken down to forms that are soluble at pH 4.6(Banks, 1998).

TABLE 1.8Methods of Influencing Cheese Ripening and Their Advantages and Disadvantages

Method of Influence Advantages Disadvantages

Increased storage temperature Easy to performNo aspects determined by law

No specific effectRisk of destroying bacteria

Increased inoculation level in starter culture

Natural enzyme balanceNo aspects determined by law

Influences pH and consistency

Addition of EnzymesProteases/peptidasesLipases, animal, and microbial

Relative low costSpecific effect

Few usable enzymesRisk of over-ripeningAspects determined by lawUse of whey

Special CulturesLactobacillus/pediococciBrevibacterium linesMoldPropionic-acid bacteria

Naturally balancedNo aspects determined by law

Opposite effect on pH and consistency

Different taste profile

Modified Starter CulturesCold/warm treatedLysozyme treatedNonacidic producing

Natural enzyme balanceEasy to conform to

Technologically complex

Source: After Kristensen, 1999. With permission.


PROCESS CHEESE

Process cheese is manufactured from one or more of the natural cheeses describedthus far. The basic premise is to stabilize the proteins that are normally affectedalready during one or more of the cheesemaking steps (Shimp, 1985). This isaccomplished by heating and mixing cheeses with some emulsifying salts. Thecareful selection of cheeses, emulsifying salts, and processing factors allows makingprocess cheeses of varied textures suitable for many end uses.

The primary reasons for manufacturing process cheese are (Spreer, 1998):

1. Long shelf life due to heat treatment and hot filling2. Wide variety due to a multitude of ingredients and composition3. Efficient utilization due to spreadable consistency and small portions4. Upgrading of defective rennet cheese products if the defects limit the shelf

life but the products are still edible

The basic steps in the manufacture of process cheese are selecting and blendingraw materials, heat processing, and forming and packaging. The raw materialsinclude the natural cheeses, emulsifying salts, and other ingredients. Using theappropriate cheeses in the blend is very critical to obtain the desired texture andflavor. The emulsifying salts, primarily phosphates and citrates, are selected for theirability to disperse and increase hydration of the cheese proteins, which createssmoothness and fat emulsification (Olson, 1995). Other ingredients vary, from dairyand nondairy products such as skim milk powder, whey protein concentrate, spicesand vegetables, and muscle food ingredients, etc. In general, good quality rawmaterials ensure good quality process cheese.

Process cheeses can be grouped into three major categories based on compositionand consistency: process cheese block, process cheese food, and process cheesespread. The selection of type of heat processing and raw materials for each are doneaccordingly. A fourth group, process cheese analog based on vegetable fat-caseinblend, is also manufactured. Specific manufacturing steps, ingredient selection, etc.,are detailed in Caric and Kalab (1993). The manufacturing conditions for sliceableand spreadable process cheese are summarized in Table 1.9.

The heat-processing step converts the raw material into a homogeneous product.Heating is performed under atmospheric pressure or vacuum at 85 to 95C or underpressure at 105 to 120C. Temperatures under 90C are desirable to avoid a browningreaction when the raw materials are high in lactose. During heating, the mix iscontinuously stirred at 60 to 140 rpm. The process duration varies from 4 to 8 minfor processed cheese blocks to 8 to 15 min for processed cheese spread (Caric andKalab, 1993).

After heat processing, the melt is conveyed to filling machines where it is moldedinto different shapes or put into containers. It can also be spread on conveyor beltsand sliced. The cheese is then cooled. Cooling is performed fairly slowly (1012 h)for process cheese blocks and very quickly (1530 min) for process cheese spreadto facilitate softening of the product.


REFERENCES

Ak, M.M. and S. Gunasekaran. 1997. Anisotropy in tensile properties of Mozzarella cheese.Journal of Food Science 62(5):10311033.

Ay, C. and S. Gunasekaran. 1994. An ultrasonic attenuation measurement for estimating milkcoagulation time. Transactions of the ASAE 37(3):857862.

Banks, J.M. 1998. Cheese. In The Technology of Dairy Products, Ed. R. Early, 81122.London, U.K.: Blackie Academic and Professional.

Battistotti, B. et al. 1984. Cheese: A Guide to the World of Cheese and Cheesemaking. NewYork: Facts on File Publications.

Bauer, R. et al. 1995. The structure of casein aggregates during renneting studied by indirectFourier transformation and inverse Laplace transformation of static and dynamiclight-scattering data, respectively. Journal of Chemical Physics 103:27252737.

Birkkjaer, H.E. et al. 1961. The influence of the cheesemaking technique upon the quality ofcheese. Report No. 128, Danish Government Research Institute for Dairy Industry,Hillerod, Denmark. (Translated from Danish and reprinted with permission in theDairy Pipeline, 1998, Center for Dairy Research, University of Wisconsin-Madison,Madison, WI, 53706, U.S.A.)

TABLE 1.9Manufacturing Conditions for Sliceable and Spreadable Process Cheese

Condition

Process Cheese Type

Sliceable Spreadable

Average age of the raw material Fresh to half-mature;mostly fresh

Combination of fresh, half-mature,and over-ripe

Relative casein contentstructure

7590%, mostly long 6075%, short to long

Melting salt Structure: not creamy Emulsifier: high molecular Polyphosphate, etc.

Structure: creamyEmulsifier: lower or medium

molecularPolyphosphate, etc.

Water, how added 1025%, all at once 2045%, in portionsTemperature 8085C (176185F) 8598C/150C (185208F/302F)Time for melting, stirring 48 min, slow 815 min, fastpH 5.45.6 5.75.9Process cheese 02% 520%Whole milk powder or whey powder 0 510%Homogenization None DesirablePackaging (filling) 515 minCooling Slow (1020 h) at room

temperatureFast (1530 min) in freezing conditions (cool air)

Treatment Very careful Intensive (powerful)

Source: After Kristensen, 1999. With permission.


Caric, M. and M. Kalab. 1993. Processed cheese products. In Cheese: Chemistry, Physicsand Microbiology, Vol. 2, Major Cheese Groups, 2nd ed., Ed. P.F. Fox, 467505.New York: Chapman and Hall.

Carlson, A., C.G. Hill, Jr., and N.F. Olson. 1987. Kinetics of milk coagulation: I-IV. Biotech-nology and Bioengineering 29(4):582589, 590600, 601611, 612624.

CFR, 1998. Cheeses and Related Cheese Products. Code of Federal Regulations, Title 21,Part 33, pp 294346. United States Department of Health and Human Services, Foodand Drug Administration, Washington.

Davis, J.G. 1965. Cheese, Vol. 1, Basic Technology. London: Churchill Livingstone.Dejmek, P. 1987. Dynamic rheology of rennet curd. Journal of Dairy Science 70:13251330.Doeff, G. 1994. Cheese in the U.S.A. Dairy Foods Sept., p. D.Fox, P.F. 1993. Cheese: an overview. In Cheese: Chemistry, Physics and Microbiology, Vol. 1,

General Aspects, Ed. P.F. Fox, 132. London: Chapman and Hall.Fox, P.F. et al. 2000. Fundamentals of Cheese Science. Gaithersburg, MD: Aspen Publishers, Inc.Fox, P.F. and P.L.H. McSweeney. 1998. Dairy Chemistry and Biochemistry. London: Blackie

Academic and Professional.Glaser, J., P.A. Carroad, and W.L. Dunkley. 1980. Electron microscopic studies of casein

micelles and curd microstructure in cottage cheese. Journal of Dairy Science63:3748.

Gunasekaran, S. and C. Ay. 1996. Milk coagulation cut-time determination using ultrasonics.Journal of Food Process Engineering 19(3):331342.

Hill, A.R. 1995. Chemical species in cheeses and their origin in milk components. In Chemi-stry of Structure-Function Relationships in Cheese, Eds. E.L. Malin and M.H. Tunick,4358. New York: Plenum Press.

Hori, T. 1985. Objective measurements of the process of curd formation during rennettreatment of milks by hot wire method. Journal of Food Science 50:911917.

Johnson, M.E. 1998. Part II Cheese chemistry. In Fundamentals of Dairy Chemistry,Ed. N.P. Wong, 634654. New York: Van Nostrand Reinhard Co.

Johnson, M. and B.A. Law. 1999. The origins, development and basic operations of cheese-making technology. In Technology of Cheesemaking, Ed. B.A. Law, 132. Sheffield,England: Sheffield Academic Press Ltd.

Kimber, A.M. et al. 1974. Electron microscope studies of the development of structure inCheddar cheese. Journal of Dairy Research 41:389396.

Kindstedt, P.S., L.J. Kiely, and J.A. Gilmore. 1992. Variation in composition and functional prop-erties within brine-salted Mozzarella cheese. Journal of Dairy Science 75:29132921.

Konuklar, G. and S. Gunasekaran. 2002. Rennet-induced milk coagulation by continuoussteady shear stress. Journal of Colloid and Interface Science (in press).

Kopelman, I.J. and U. Cogan. 1976. Determination of clotting power of milk clotting enzymes.Journal of Dairy Science 59(2):196199.

Kristensen, J.M.B. 1999. Cheese Technology A Northern European Approach. Aarhus,Denmark: International Dairy Books.

Kristoffersen, T. 1985. Development of flavor in cheese. Milchwissenschaft 40:197199.Law, B.A. (ed.) 1999. Technology of Cheesemaking. Boca Raton, FL: Sheffield Academic

Press.Lomholt, S.B. and K.B. Qvist. 1999. The formation of cheese curd. In Technology of Cheese-

making, Ed. B.A. Law. Sheffield, England: Sheffield Academic Press Ltd.Lopez, M.B., S.B. Lomholt, and Q.B. Qvist. 1998. Rheological properties and cutting time

of rennet gels: effect of pH and enzyme concentration. International Dairy Journal8:289293.


NDC. 2000. Newer Knowledge of Dairy Foods/Cheese. National Dairy Council(www.nationaldairycouncil.org). Managed by Dairy Management Inc., Rosemont, IL.

Nilson, K.M. 1968. Some practical problems and their solutions in the manufacture ofMozzarella cheese. In Proc. 5th Annual Marschall Italian Cheese Seminar, 17.Madison, WI.

Oberg, C.J., W.R. McManus, and D.J. McMahon. 1993. Microstructure of Mozzarella cheeseduring manufacture. Food Structure 12:251258.

OCallaghan, D.J., C.P. ODonnell, and F.A. Payne. 1999. A comparison of on-line techniquesfor determination of curd setting time using cheese milks under different rates ofcoagulation. Journal of Food Engineering 41(1):4354.

Olson, N.F. 1979. Cheese. In Microbial Technology II, Eds. H.J. Peppler and D. Perlman,3977. New York: Academic Press.

Olson, N.F. 1995. Cheese. In Biotechnology, Vol. 9, Eds. H.-J. Rehm and G. Reed, 355384.Weinheim, Germany: Verlag Chemie.

Paulson, B.M., D.J. McMahon, and C.J. Oberg. 1998. Influence of sodium chloride onappearance, functionality and protein arrangements in non-fat Mozzarella cheese.Journal of Dairy Science 81:20532064.

Payne, F.A. et al. 1993. Fiber optic sensor for predicting the cutting time of coagulating milkfor cheese production. Transactions of the ASAE 36(3):841847.

Pearse, M.J. and A.G. Mackinlay. 1989. Biochemical aspects of syneresis: A review. Journalof Dairy Science 72:14011407.

Prentice, J.H. 1993. Cheese rheology. In Cheese: Chemistry, Physics & Microbiology, Vol. 1,General Aspects, Ed. P.F. Fox, 303340. Elsevier Applied Science, London.

Scott, R., R.K. Robinson, and R.A. Wilbey. 1998. Cheesemaking Practice. Gaithersburg, MD:Aspen Publishers, Inc.

Shimp, L.A. 1985. Process cheese principles. Food Technology 39(5):6369.Spreer, E. 1998. Milk and Dairy Product Technology. New York: Marcel Dekker, Inc.Turhan, M. and S. Gunasekaran. 1998. Analysis of moisture diffusion in white cheese during

salting. Milchwissenschaft 54(8):446450.Uludogan, G. 1999. Evaluation of Milk Coagulation Using Ultrasonic and Rheological Meth-

ods, Ph.D. thesis, University of Wisconsin-Madison.Vedamuthu, E.R. and C. Washam. 1983. Cheese. In Biotechnology A Comprehensive

Treatise, Vol. 5, Eds. H.-J. Rehm and G. Reed, 231313. Weinheim, Germany: VerlagChemie.

Visser, J. 1991. Factors affecting the rheological and fracture properties of hard and semihardcheese. Bulletin of the International Dairy Federation No. 268, 4961, IDF, Brussels,Belgium.

Walstra, P. and R. Jenness. 1984. Dairy Chemistry and Physics. New York: John Wiley and Sons.Walstra, P. et al. 1999. Dairy Technology Principles of Milk Properties and Processes.

New York: Marcel Dekker, Inc.


Fundamental Rheological Methods

Fundamental rheological methods are performed under well-defined and controlledconditions. Though some assumptions about the materials and test methods may bemade, calculations of material properties are based on well-defined rheological terms(e.g., strain, stress). Moreover, material properties determined by fundamental methodsare independent of the apparatus used for measurements, which allows comparison ofdata from different research groups (Mitchell, 1984; Shoemaker et al., 1987; Tunickand Nolan, 1992; Tunick, 2000). These fundamental methods help researchers studycheese properties and effects of many manufacturing factors, and eventually developcheeses with desired and consistent textural and rheological properties. Few reviewshave been published on the fundamental rheological methods employed in cheeseresearch (van Vliet, 1991a; Konstance and Holsinger, 1992; Luyten et al., 1992).

DEFINITION OF RHEOLOGY

The term

rheology

was coined by Professor E.C. Bingham to represent a new branchof mechanics concerned with

the study of deformation and flow of matter

(Reiner,1964). This definition was accepted at the inaugural meeting of the Society ofRheology (then, the American Society of Rheology) in 1929. Although significantrheology research has been performed prior to this date, the progress in the field ofrheology seems to have greatly accelerated after its inception in 1929 as a separatediscipline (Doraiswamy, 2002). Rheology is now a well-recognized field with manyapplications in different industries. Professionals from various disciplines (e.g.,physicists, chemists, biologists, engineers, mathematicians) are interested in thetheoretical and practical aspects of rheology.

As stated in the definition, rheology aims at measuring those properties ofmaterials that control their deformation and flow behavior when subjected toexternal forces. Thus, rheology is mainly concerned with the relationship betweenstrain, stress, and time. When subjected to external forces, solids (or truly elasticmaterials) will deform, whereas liquids (or truly viscous materials) will flow.However, contemporary rheology is more interested in the behavior of real mate-rials with properties intermediate between those of ideal solids and ideal liquids(Doraiswamy, 2002). These industrially important materials are called viscoelasticmaterials, which include almost all real materials.

BASIC CONCEPTS

Rheology deals with the relationship between three variables: strain, stress, and time.Strain and stress are related to deformation and force, respectively. Strain accounts

2


for the size effect on material deformation due to difference in length (or height) ofspecimens, whereas stress accounts for the size effect on applied force due todifference in cross-sectional area of specimens. Using strain and stress, rheologistsare able to obtain true material properties independent of the sample size andgeometry, and compare test results for samples of different sizes and geometries.Many rheological terms are defined and described by van Vliet (1991b).

S

TRAIN

When a material is subjected to an external force, individual points of the body willmove relative to one another causing a change in the size and shape of the material.The

deformation

is the measure of such a change in size and shape. Deformation,however, is not uniquely related to force as illustrated in the following example.Two specimens (

A

and

B

), made of the same material and having identical shapeand size, are subjected to the same axial force,

F

, applied

perpendicular

to thematerial surfaces (Figure 2.1). This will result in the same amount of extension

FIGURE 2.1

Effect of test specimen length on forceextension relationship. (After Hall, 1968).

FF

FF

Before deformation

After deformation A

A

Before deformation

After deformation B

B

BABefore deformation Before deformation

After deformation After deformation BA

F F

L

L

L/2

L/2

L L

L/2

L/2

Deformation = L

Total deformation = 2L

Deformation = L

Lo

Lo

2 L

2 Lo


(or deformation), denoted by

L

. Let us now imagine that we join the two specimensend to end and again apply the same axial force

F

. Since each specimen willexperience the same axial force as they did when stretched separately, they eachwill extend to the same amount as before (i.e.,

L

) giving a total extension of 2

L

.

However, when we divide the total extension 2

L

by the total original length 2

L

o

,

the resulting quantity has the same numerical value as when the specimens werestretched separ

Documents

Cheese Re )