Brewing
Science and practice
Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes and
Roger Stevens
Published by Woodhead Publishing Limited, Abington Hall, Abington
Cambridge CB1 6AH, England
www.woodhead-publishing.com
Published in North America by CRC Press LLC, 2000 Corporate Blvd, NW
Boca Raton FL 33431, USA
First published 2004, Woodhead Publishing Limited and CRC Press LLC
ß 2004, Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes and Roger Stevens
The authors have asserted their moral rights.
This book contains information obtained from authentic and highly regarded sources. Reprinted
material is quoted with permission, and sources are indicated. Reasonable efforts have been
made to publish reliable data and information, but the authors and the publishers cannot assume
responsibility for the validity of all materials. Neither the authors nor the publishers, nor anyone
else associated with this publication, shall be liable for any loss, damage or liability directly or
indirectly caused or alleged to be caused by this book.
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A catalogue record for this book is available from the British Library.
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A catalog record for this book is available from the Library of Congress.
Woodhead Publishing Limited ISBN 1 85573 490 7 (book) 1 85573 906 2 (e-book)
CRC Press ISBN 0-8493-2547-1
CRC Press order number: WP2547
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The two volumes of the second edition of Malting and Brewing Science I, Malt and Sweet
Wort and II, Hopped Wort and Beer, by James S. Hough, Dennis E. Briggs, Roger
Stevens and Tom W. Young, appeared in 1981 and 1982. This book provided the
framework for the M.Sc. in Malting and Brewing Science, the course that was offered by
the British School of Malting and Brewing in the University of Birmingham (UK). It also
provided the backbone of many other courses. After more than 20 years the demand for
these volumes has continued, although they are increasingly out of date. Malts and
Malting, by Dennis E. Briggs, appeared in 1998, and Brewing Yeast and Fermentation,
by Chris Boulton and David Quain, became available in 2001. These books cover their
named topics in depth. However, the need for an up-to-date, integrated textbook on
brewing, comparable in scope and depth of coverage to Malting and Brewing Science,
remained.
Brewing: Science and practice is intended to meet this need. Deciding on the details of
the coverage has given rise to some anxious discussions. Practically it is impossible to
describe all aspec ts of all the varieties of brewing processes in depth, in one moderately
sized volume. Inevitably it has been necessary to assume some background knowledge of
physics, chemistry, biology, and engineering. However, the book is understandable to
people without detailed knowledge in these areas. The references at the end of each

chapter provide guidance for further reading. Since the wide range of kinds of brewing
operations, from simple, low-volume, single-line breweries to extremely large, highly
complex, multiple-line installations, does not allow a single description of brewing
activities, the book concentrates on the principles of the variou s brewing processes.
Brewing is carried out all over the world and, unsurprisingly, different terminologies
and methods of measurement and analysis are used. The different systems of units and
analyses are explained in the text and conversion factors (where valid) and some other
useful data are given in the Appendix. A list of abbreviations is included in the index for
reference. The index also includes a list of formulae
First of all the authors warmly thank our wives, Rosemary, Wendy, Stella and Betty,
for their unfailing patience and good-humoured support. We have also been given a great
deal of help from our colleagues and friends. We are grateful to Mrs Doreen Hough for
Preface
permission to use some of the late Professor Jim Hough's diagrams. Permission to use
other diagrams is acknowledged in the text. We would like to thank: Mrs Marjorie
Anderson, Dr John M. H. Andrews, Mrs Marjorie Anderson, Dr Raymond G. Anderson,
Mr David J. Banfield, Mr Zane C. Barnes, Herr Volker Borngraber, Mr Andy Carter, Dr
Peter Darby, Mr J. Brian Eaton, Dr David L. Griggs, Dr Paul K. Hegarty, Mrs Sue M.
Henderson, Mr James Johnstone, Mr Roy F. Lindsay, Dr G. C. Linsley-Noakes, Dr David
E. Long, Mr John MacDonald, Dr Ray Marriott, Mr P. A. (Tom) Martin, Dr A. Peter
Maule, Ms Elaine McCrimmon, Dr Philip Morrall, Dr Ray Neve, Dr George Philliskirk,
Dr David E. Quain, Mr Trevor R. Roberts, Mr Derek Wareham and Dr Richard D. J.
Webster. We also wish to thank Coors Brewers for the use of the Technical Centre,
Burton-on-Trent.
We apologise if any acknowledgements have been omitted.
xviii Preface
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Contents
Preface xvii

1. An Outline of Brewing 1
1.1 Introduction 1
1.2 Malts 1
1.3 Mash Tun Adjuncts 2
1.4 Brewing Liquor 2
1.5 Milling and Mashing in 2
1.6 Mashing and Wort Separation Systems 3
1.7 The Hop-Boil and Copper Adjuncts 4
1.8 Wort Clarification, Cooling and Aeration 4
1.9 Fermentation 5
1.10 The Processing of Beer 5
1.11 Types of Beer 6
1.12 Analytical Systems 7
1.13 The Economics of Brewing 8
1.14 Excise 9
1.15 References and Further Reading 9
1.15.1 The Systems of Malting and Brewing Analysis 9
1.15.2 General 9
2. Malts, Adjuncts and Supplementary Enzymes 11
2.1 Grists and Other Sources of Extract 11
2.2 Malting 11
2.2.1 Malting in Outline 11
2.2.2 Changes Occurring in Malting Grain 14
2.2.3 Malting Technology 19
2.2.4 Malt Analyses 21
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2.2.5 Types of Kilned Malt 26
2.2.6 Special Malts 31

2.2.7 Malt Specifications 32
2.3 Adjuncts 34
2.3.1 Mash Tun Adjuncts 34
2.3.2 Copper Adjuncts 40
2.4 Priming Sugars, Caramels, Malt Colourants and
Farbebier 45
2.5 Supplementary Enzymes 46
2.6 References 50
3. Water, Effluents and Wastes 52
3.1 Introduction 52
3.2 Sources of Water 53
3.3 Preliminary Water Treatments 57
3.4 Secondary Water Treatments 60
3.5 Grades of Water Used in Breweries 64
3.6 The Effects of Ions on the Brewing Process 65
3.7 Brewery Effluents, Wastes and by-Products 68
3.7.1 The Characterization of Waste Water 69
3.7.2 The Characteristics of Some Brewery Wastes
and by-Products 71
3.8 The Disposal of Brewery Effluents 73
3.8.1 Preliminary Treatments 73
3.8.2 Aerobic Treatments of Brewery Effluents 75
3.8.3 Sludge Treatments and Disposal 78
3.8.4 Anaerobic and Mixed Treatments of Brewery
Effluents 79
3.9 Other Water Treatments 82
3.10 References 82
4. The Science of Mashing 85
4.1 Introduction 85
4.2 Mashing Schedules 88

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4.3 Altering Mashing Conditions 95
4.3.1 The Grist 95
4.3.2 Malts in Mashing 97
4.3.3 Mashing with Adjuncts 101
4.3.4 The Influence of Mashing Temperatures and
Times on Wort Quality 104
4.3.5 Non-Malt Enzymes in Mashing 110
4.3.6 Mashing Liquor and Mash pH 113
4.3.7 Mash Thickness, Extract Yield and Wort Quality 116
4.3.8 Wort Separation and Sparging 119
4.4 Mashing Biochemistry 122
4.4.1 Wort Carbohydrates 122
4.4.2 Starch Degradation in Mashing 127
4.4.3 Non-Starch Polysaccharides in Mashing 136
4.4.4 Proteins, Peptides and Amino Acids 142
4.4.5 Nucleic Acids and Related Substances 146
4.4.6 Miscellaneous Substances Containing Nitrogen 146
4.4.7 Vitamins and Yeast Growth Factors 149
4.4.8 Lipids in Mashing 151
4.4.9 Phenols 157
4.4.10 Miscellaneous Acids 161
4.4.11 Inorganic Ions in Sweet Wort 163
4.5 Mashing and Beer Flavour 164
4.6 Spent Grains 166
4.7 References 167
5. The Preparation of Grists 171
5.1 Intake, Handling and Storage of Raw Materials 171

5.2 The Principles of Milling 175
5.3 Laboratory Mills 178
5.4 Dry Roller Milling 179
5.5 Impact Mills 182
5.6 Conditioned Dry Milling 184
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5.7 Spray Steep Roller Milling 184
5.8 Steep Conditioning 186
5.9 Milling under Water 187
5.10 Grist Cases 187
5.11 References 188
6. Mashing Technology 189
6.1 Introduction 189
6.2 Mashing in 190
6.3 The Mash Tun 194
6.3.1 Construction 194
6.3.2 Mash Tun Operations 198
6.4 Mashing Vessels for Decoction, Double Mashing and
Temperature-Programmed Infusion Mashing
Systems 199
6.4.1 Decoction and Double Mashing 199
6.4.2 Temperature-Programmed Infusion Mashing 201
6.5 Lauter Tuns 203
6.6 The Strainmaster 211
6.7 Mash Filters 212
6.8 The Choice of Mashing and Wort Separation
Systems 217
6.9 Other Methods of Wort Separation and Mashing 220

6.10 Spent Grains 222
6.11 Theory of Wort Separation 222
6.12 References 225
7. Hops 227
7.1 Introduction 227
7.2 Botany 228
7.3 Cultivation 230
7.4 Drying 234
7.5 Hop Products 236
7.5.1 Hop Pellets 236
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7.5.2 Hop Extracts 238
7.5.3 Hop Oils 239
7.6 Pests and Diseases 240
7.6.1 Damson-Hop Aphid (Phorodon Humuli
Schrank) 240
7.6.2 (Red) Spider Mite (Tetranchus Urticae Koch) 243
7.6.3 Other Pests 244
7.6.4 Downy Mildew (Pseudoperonospora Humuli
(Miyabe and Tak.) G. W. Wilson) 244
7.6.5 Powdery Mildew (Sphaerotheca Macularis (DC.)
Burr) 245
7.6.6 Verticillium Wilt (Verticillium Albo-Atrum Reinke
and Berth) 246
7.6.7 Virus Diseases 247
7.7 Hop Varieties 248
7.8 References 254
8. The Chemistry of Hop Constituents 255

8.1 Introduction 255
8.2 Hop Resins 256
8.2.1 Introduction 256
8.2.2 Biosynthesis of the Hop Resins 265
8.2.3 Analysis of the Hop Resins 267
8.2.4 Isomerization of the α-Acids 269
8.2.5 Hard Resins and Prenylflavonoids 277
8.2.6 Oxidation of the Hop Resins 280
8.3 Hop Oil 283
8.3.1 Introduction 283
8.3.2 Hydrocarbons 286
8.3.3 Oxygen-Containing Components 288
8.3.4 Sulphur-Containing Compounds 295
8.3.5 Most Potent Odorants in Hop Oil 297
8.3.6 Hop Oil Constituents in Beer 298
8.3.7 Post Fermentation Aroma Products 300
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8.4 Hop Polyphenols (Tannins) 301
8.5 Chemical Identification of Hop Cultivars 302
8.6 References 303
9. Chemistry of Wort Boiling 306
9.1 Introduction 306
9.2 Carbohydrates 307
9.3 Nitrogenous Constituents 307
9.3.1 Introduction 307
9.3.2 Proteins 309
9.4 Carbohydrate-Nitrogenous Constituent Interactions 311
9.4.1 Melanoidins 319

9.4.2 Caramel 320
9.5 Protein-Polyphenol (Tannin) Interactions 322
9.6 Copper Finings and Trub Formation 322
9.7 References 324
10. Wort Boiling, Clarification, Cooling and Aeration 326
10.1 Introduction 326
10.2 The Principles of Heating Wort 328
10.3 Types of Coppers 332
10.4 The Addition of Hops 341
10.5 Pressurized Hop-Boiling Systems 342
10.5.1 Low-Pressure Boiling 342
10.5.2 Dynamic Low-Pressure Boiling 343
10.5.3 Continuous High-Pressure Boiling 343
10.6 The Control of Volatile Substances in Wort 343
10.7 Energy Conservation and the Hop-Boil 345
10.8 Hot Wort Clarification 349
10.9 Wort Cooling 356
10.10 The Cold Break 358
10.11 Wort Aeration/Oxygenation 359
10.12 References 360
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11. Yeast Biology 363
11.1 Historical Note 363
11.2 Taxonomy 366
11.3 Yeast Ecology 369
11.4 Cellular Composition 371
11.5 Yeast Morphology 372
11.6 Yeast Cytology 373

11.6.1 Cell Wall 374
11.6.2 The Periplasm 379
11.6.3 The Plasma Membrane 379
11.6.4 The Cytoplasm 380
11.6.5 Vacuoles and Intracellular Membrane
Systems 381
11.6.6 Mitochondria 382
11.6.7 The Nucleus 382
11.7 Yeast Cell Cycle 384
11.7.1 Yeast Sexual Cycle 387
11.8 Yeast Genetics 389
11.8.1 Methods of Genetic Analysis 390
11.8.2 The Yeast Genome 393
11.9 Strain Improvement 395
11.10 References 399
12. Metabolism of Wort by Yeast 401
12.1 Introduction 401
12.2 Yeast Metabolism – an Overview 404
12.3 Yeast Nutrition 406
12.3.1 Water Relations 407
12.3.2 Sources of Carbon 409
12.3.3 Sources of Nitrogen 410
12.3.4 Sources of Minerals 410
12.3.5 Growth Factors 410
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12.4 Nutrient Uptake 411
12.4.1 Sugar Uptake 412
12.4.2 Uptake of Nitrogenous Nutrients 415

12.4.3 Lipid Uptake 416
12.4.4 Ion Uptake 416
12.4.5 Transport of the Products of Fermentation 418
12.5 Sugar Metabolism 418
12.5.1 Glycolysis 418
12.5.2 Hexose Monophosphate (Pentose Phosphate)
Pathway 421
12.5.3 Tricarboxylic Acid Cycle 422
12.5.4 Electron Transport and Oxidative
Phosphorylation 425
12.5.5 Fermentative Sugar Catabolism 428
12.5.6 Gluconeogenesis and the Glyoxylate Cycle 430
12.5.7 Storage Carbohydrates 430
12.5.8 Regulation of Sugar Metabolism 434
12.5.9 Ethanol Toxicity and Tolerance 438
12.6 The Role of Oxygen 440
12.7 Lipid Metabolism 442
12.7.1 Fatty Acid Metabolism 443
12.7.2 Phospholipids 445
12.7.3 Sterols 447
12.8 Nitrogen Metabolism 449
12.9 Yeast Stress Responses 453
12.10 Minor Products of Metabolism Contributing to Beer
Flavour 454
12.10.1 Organic and Fatty Acids 454
12.10.2 Carbonyl Compounds 456
12.10.3 Higher Alcohols 459
12.10.4 Esters 460
12.10.5 Sulphur-Containing Compounds 462
12.11 References 465

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13. Yeast Growth 469
13.1 Introduction 469
13.2 Measurement of Yeast Biomass 470
13.3 Batch Culture 474
13.3.1 Brewery Batch Fermentations 477
13.3.2 Effects of Process Variables on Fermentation
Performance 478
13.4 Yeast Ageing 482
13.5 Yeast Propagation 483
13.5.1 Maintenance and Supply of Yeast Cultures 484
13.5.2 Laboratory Yeast Propagation 486
13.5.3 Brewery Propagation 487
13.6 Fed-Batch Cultures 490
13.7 Continuous Culture 492
13.8 Immobilized Yeast Reactors 495
13.9 Growth on Solid Media 497
13.10 Yeast Identification 498
13.10.1 Microbiological Tests 498
13.10.2 Biochemical Tests 499
13.10.3 Tests Based on Cell Surface Properties 500
13.10.4 Non-Traditional Methods 501
13.11 Measurement of Viability 502
13.12 Assessment of Yeast Physiological State 504
13.13 References 506
14. Fermentation Technologies 509
14.1 Introduction 509
14.2 Basic Principles of Fermentation Technology 510

14.2.1 Fermentability of Wort 510
14.2.2 Time Course of Fermentation 511
14.2.3 Heat Output in Fermentation 512
14.3 Bottom Fermentation Systems 514
14.3.1 Choice, Size and Shape of Vessels 514
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14.3.2 Construction of Cylindroconical Vessels 516
14.3.3 Operation of Cylindroconical Vessels 519
14.4 Top Fermentation Systems 526
14.4.1 Traditional Top Fermentation 526
14.4.2 Yorkshire Square Fermentation 529
14.4.3 Burton Union Fermentation 531
14.5 Continuous Fermentation 532
14.5.1 Early Systems of Continuous Fermentation 533
14.5.2 The New Zealand System 535
14.5.3 Continuous Primary Fermentation with
Immobilized Yeast 535
14.6 Fermentation Control Systems 539
14.6.1 Specific Gravity Changes 539
14.6.2 Other Methods 540
14.7 Summary 541
14.8 References 541
15. Beer Maturation and Treatments 543
15.1 Introduction 543
15.2 Maturation: Flavour and Aroma Changes 544
15.2.1 Principles of Secondary Fermentation 544
15.2.2 Important Flavour Changes 545
15.2.3 Techniques of Maturation 547

15.2.4 Flavour, Aroma and Colour Adjustments by
Addition 549
15.2.5 Maturation Vessels 552
15.3 Stabilization against Non-Biological Haze 555
15.3.1 Mechanisms for Haze Formation 555
15.3.2 Removal of Protein 556
15.3.3 Removal of Polyphenols 559
15.3.4 Combined Treatments to Remove Protein and
Polyphenols 561
15.3.5 Hazes from Other Than Protein or Polyphenols 561
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15.4 Carbonation 562
15.4.1 Carbon Dioxide Saturation 562
15.4.2 Carbon Dioxide Addition 564
15.4.3 Carbon Dioxide Recovery 565
15.5 Clarification and Filtration 567
15.5.1 Removal of Yeast and Beer Recovery 567
15.5.2 Beer Filtration 574
15.6 Special Beer Treatments 582
15.6.1 Low-Alcohol and Alcohol-Free Beers 582
15.6.2 Ice Beers 585
15.6.3 Diet Beers 586
15.7 Summary 587
15.8 References 587
16. Native African Beers 589
16.1 Introduction 589
16.1.1 An Outline of the Stages of Production 590
16.1.2 Bouza 590

16.1.3 Merissa 591
16.1.4 Busaa and Some Other Beers 591
16.1.5 Southern African Beers 592
16.2 Malting Sorghum and Millets 593
16.3 Brewing African Beers on an Industrial Scale 597
16.4 Attempts to Obtain Stable African Beers 601
16.5 Beer Composition and Its Nutritional Value 602
16.6 References 604
17. Microbiology 606
17.1 Introduction 606
17.2 The Microbiological Threat to the Brewing Process 607
17.3 Beer Spoilage Micro-Organisms 610
17.3.1 Detection of Brewery Microbial Contaminants 610
17.3.2 Identification of Brewery Bacteria 613
17.3.3 Gram Negative Beer Spoiling Bacteria 614
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17.3.4 Gram Positive Beer Spoiling Bacteria 621
17.3.5 Beer Spoilage Yeasts 625
17.3.6 Microbiological Media and the Cultivation of
Micro-Organisms 628
17.4 Microbiological Quality Assurance 632
17.5 Sampling 634
17.5.1 Sampling Devices 634
17.6 Disinfection of Pitching Yeast 636
17.7 Cleaning in the Brewery 637
17.7.1 Range of Cleaning Operations 640
17.7.2 CIP Systems 643
17.7.3 Cleaning Agents 644

17.7.4 Cleaning Beer Dispense Lines 647
17.7.5 Validation of CIP 648
17.8 References 648
18. Brewhouses: Types, Control and Economy 650
18.1 Introduction 650
18.2 History of Brewhouse Development 650
18.2.1 The Tower Brewery Lay-Out 651
18.2.2 The Horizontal Brewery Lay-Out 653
18.3 Types of Modern Brewhouses 654
18.3.1 Experimental Brewhouses 654
18.3.2 Micro- and Pub Breweries 655
18.4 Control of Brewhouse Operations 657
18.4.1 Automation in the Brewhouse 657
18.4.2 Scheduling of Brewhouse Operations 658
18.5 Economic Aspects of Brewhouses 660
18.6 Summary 661
18.7 References 661
19. Chemical and Physical Properties of Beer 662
19.1 Chemical Composition of Beer 662
19.1.1 Inorganic Constituents 664
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19.1.2 Alcohol and Original Extract 666
19.1.3 Carbohydrates 670
19.1.4 Other Constituents Containing Carbon,
Hydrogen and Oxygen 672
19.1.5 Nitrogenous Constituents 685
19.1.6 Sulphur-Containing Constituents 691
19.2 Nutritive Value of Beer 694

19.3 Colour of Beer 695
19.4 Haze 697
19.4.1 Measurement of Haze 698
19.4.2 Composition and Formation of Haze 699
19.4.3 Prediction of Haze and Beer Stability 700
19.4.4 Practical Methods for Improving Beer Stability 702
19.5 Viscosity 702
19.6 Foam Characteristics and Head Retention 703
19.6.1 Methods of Assessing Foam Characteristics 704
19.6.2 Beer Components Influencing Head Retention 707
19.6.3 Head Retention and the Brewing Process 709
19.7 Gushing 710
19.8 References 712
20. Beer Flavour and Sensory Assessment 716
20.1 Introduction 716
20.2 Flavour – Taste and Odour 717
20.3 Flavour Stability 728
20.4 Sensory Analysis 733
20.5 References 757
21. Packaging 759
21.1 Introduction 759
21.2 General Overview of Packaging Operations 760
21.3 Bottling 761
21.3.1 Managing the Bottle Flow 762
21.3.2 Managing the Beer Flow 770
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21.3.3 Managing Plant Cleaning 785
21.3.4 Materials for Making Bottles 786

21.4 Canning 787
21.4.1 The Beer Can 787
21.4.2 Preparing Cans at the Brewery for Filling 788
21.4.3 Can Filling 789
21.4.4 Can Closing (Seaming) 790
21.4.5 Widgets in Cans 792
21.5 Kegging 792
21.5.1 The Keg 793
21.5.2 Treatment of Beer for Kegging 794
21.5.3 Handling of Kegs 796
21.5.4 Keg Internal Cleaning and Filling 797
21.5.5 Keg Capping and Labeling 802
21.5.6 Smooth Flow Ale in Kegs 803
21.6 Cask Beer 805
21.6.1 The Cask 805
21.6.2 Handling Casks 806
21.6.3 Preparing Beer for Cask Filling 807
21.6.4 Cask Filling 808
21.7 Summary 809
21.8 References 810
22. Storage and Distribution 812
22.1 Introduction 812
22.2 Warehousing 812
22.2.1 Principles of Warehouse Operation 813
22.2.2 Safety in the Warehouse 814
22.3 Distribution 815
22.3.1 Logistics 815
22.3.2 Quality Assurance 817
22.4 Summary 818
22.5 References 818

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23. Beer in the Trade 819
23.1 Introduction 819
23.2 History 820
23.3 Beer Cellars 820
23.3.1 Hygiene 820
23.3.2 Temperature 821
23.3.3 Lighting 821
23.4 Beer Dispense 821
23.4.1 Keg Beer 822
23.4.2 Cask Beer 824
23.4.3 Bottled and Canned Beer 830
23.5 Quality Control 830
23.6 New Developments in Trade Quality 830
23.7 Summary 831
23.8 References 831
Appendix: Units and Some Data of Use in Brewing 832
Table A1. SI Derived Units 833
Table A2. Prefixes for SI Units 834
Table A3. Comparison of Thermometer Scales 835
Table A4. Interconversion Factors for Units of
Measurement 837
Table A5. Specific Gravity and Extract Table 838
Table A6. Equivalence between Institute of Brewing Units
of Hot Water Extract 841
Table A7. Solution Divisors of Some Sugars 842
Table A8. Some Properties of Water at Various
Temperatures 842

Table A9. The Density and Viscosity of Water at Various
Temperatures 842
Table A10. Some More Properties of Water 843
Table A11. The Relationship Between the Absolute Pressure
and the Temperature of Water-Saturated Steam 843
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Table A12. The Solubility of Pure Gases in Water at
Different Temperatures 844
Table A13. Salts in Brewing Liquors 844
Table A14. Units of Degrees of Water Hardness 845
Table A15. Characteristics of Some Brewing Materials 845
Table A16. Pasteurization Units 846
Fig. A1. The Relationships between Ethanol/Water
Mixtures and the Densities of the Solutions 847
References 847
Index 848
1.1 Introduction
Beers and beer-like beverages may be prepared from raw cereal grains, malted cereal grains
and (historically) bread. This book is primarily concerned with beers of the types that
originated in Europe, but which are now produced world-wide. However, an account is
given of `African-style' beers (Chapter 16). The most simple preparation of European-style
beers involves (a) incubating and extracting malted, ground up cereal grains (usually
barley) with warm water. Sometimes the ground malt is mixed with other starchy materials
and/or enzymes. (b) The solution obtained is boiled with hops or hop preparations. (c) The
boiled solution is clarified and cooled. (d) The cooled liquid is fermented by added yeast.
Usually the beer is clarified, packaged and served while effervescent with escaping carbon
dioxide. In this chapter the preparation of beers is outlined and the brewers' vocabulary is
introduced. Beers are made in amounts ranging from a few hectolitres (hl) a week to

thousands of hl. They are made using various different systems of brewing.
1.2 Malts
Malts are made from selected cereal grain, usually barley, (but sometimes wheat, rye,
oats, sorghum or millet), that has been cleaned and stored until dormancy has declined
and it is needed. It is then germinated under controlled conditions. Their preparation is
outlined in Chapter 2, and is described in detail in Briggs (1998). The grain is hydrated,
or `steeped', by immersion in water. During steeping the water will be changed at least
once, air may be sucked through the grain during `dry' periods between immersions, and
may be blown into the grain while immersed. After steeping the grain is drained and is
germinated to a limited extent in a cool, moist atmosphere with occasional turning and
mixing to prevent the rootlets matting together. During germination the acrospire
(coleoptile) grows beneath the husk and rootlets grow from the end of the grain, enzymes
accumulate and so do sugars and other soluble materials. The dead storage tissue of the
grain, the starchy endosperm, is partly degraded, or `modified', and its physical strength
1
An outline of brewing
is reduc ed. When germination and `modification' are sufficiently advanced they are
stopped by kilning. The `green malt' (green in the sense of immatur e, it is not green in
colour) is kilned, that is, it is dried and lightly cooked, or cured, in a current of warm to
hot air. Pale, `white' malts are kilned using low temperatures and in these enzyme
survival is considerable. In darker, coloured malts, kilned using higher temperatures,
enzyme survival is less. In extreme cases the darkest, special malts are heated in a
roasting drum and contain no active enzymes. After kilning the malt is cooled and
`dressed', that is, the brittle rootlets (`culms', sprouts) are broken off and they and dust
are removed. The culms are usually used for cattle food. Pale malts are usually stored for
some weeks before use. In contrast to the tough, ungerminated barley grain malt is
`friable', that is, it is easily crushed.
1.3 Mash tun adjuncts
Mash tun adjuncts are preparations of cereals (e.g., flaked maize or rice flakes, wheat
flour, micronized wheat grains, or rice or maize grits which have to be cooked separately

in the brewery) which may be mixed with ground malt in the mashing process. The use of
an adjunct alters the character of the beer produced. An adjunct's starch is hydrolysed
during mashing by enzymes from the malt, so providing a (sometimes) less expensive
source of sugars as well as changing the character of the wort. Sometimes microbial
enzymes are added to the mash. In a few countries the use of adjuncts is forbidde n. In
Germany the Reinheitsgebot stipulates that beer may be made only with water, malt, hops
and yeast.
1.4 Brewing liquor
In brewing, water is commonly known as liquor. It is used for many purposes besides
mashing, including beer dilution at the end of high-gravity brewing, cleaning and in
raising steam . Water for each purpose must meet different quality criteria (Chapter 3).
The brewing liquor used in mashing must be essentially `pure', but it must contain
dissolved salts appropriate for the beer being made. The quality of the liquor influences
the character of the beer made from it. Famous brewing locations gained their
reputations, at least in part, from the qualities of the liquors available to them. Thus
Burton-on-Trent is famous for its pale ales, Dublin for its stouts and Pilsen for its fine,
pale lagers. It is now usual, at least in larger breweries, to adjust the composition of the
brewing liquor (Chapter 3).
1.5 Milling and mashing in
The malt, sometimes premixed with particular adjuncts, is broken up to a controlled
extent by milling to create the `grist'. The type of mill used and the extent to which the
malt (and adjunct) is broken down is chosen to suit the types of mashing and wort-
separation syst ems being used (Chapter 5). If dry milling is used the grist, possibly mixed
with adjuncts, is collected in a container, the grist case.
At mashing-in (doughing-in) the grist is intimately mixed with brewing liquor, both
flowing at controlled rates, into a mashing vessel at an exactly controlled temperature.
2 Brewing: science and practice
The resulting `mash', with the consistency of a thin slurry, is held for a period of
`conversion'. The objective is to obtain a mash that wi ll yield a suitable `sweet wort', a
liquid rich in materials dissolved from the malt and any adjuncts that have been used. The

dissolved material, the `extract', contains soluble substances that were preformed in the
grist and other substances (esp ecially carbohydrates derived from starch), that are formed
from previously insoluble materials by enzyme-catalysed hydrolytic breakdown during
mashing.
1.6 Mashing and wort separation systems
The major mashing systems are, broadly, (a) the simplest, nearly isotherm al, infusion
mashing system, (traditional for British ale brewers); (b) the decoction system,
(traditional for mainland European lage r brewers); (c) the double mash system, (common
in North American practice); (d) the temperature-programmed infusion mashing system
that is being widely adopted in the UK and mainland Europe (Chapters 4 and 5). A mash
should be held at a chosen temperature (or at successive different temperatures), for pre-
determined times, to allow enzymes to `convert' (degrade) the starch and dextrins to
soluble sugars, to cause the partial breakdown of proteins, to degrade nucleic acids and
other substances. At the end of mashin g the sweet, or unhopped wort (the solution of
extractives, mainly carbohydrates; the `extract') is separated from the undissolved solids,
the spent grains or draff.
Infusion mashing is carried out in mash tuns. Mash conversion and the separation of
the sweet wort from the spent grains take place in this vessel. The coarsely ground grist,
made with a high proportion of well-modified malt, is mashed in to give a relatively
thick, porridge-like mash at 63À67 ëC (145.4À152.6 ëF). After a stand of between 30
minutes and two and a half hours the wort (liquid) is withdrawn from the mash. The first
worts are cloudy and are re-circulated, but as the run off is continued the wort becomes
`bright' (clear), because it is filtered through the bed of grist particles. When bright the
wort is either collected in a holding vessel (an underback) or it is moved directly to a
copper to be boiled with hops. Most of the residual extract, initially entrained in the wet
grains, is washed out by sparging (spraying) hot liquor, at 75À80 ëC (167À176 ëF ) over
the goods.
Decoction mashing is carried out with more finely ground grists, originally made with
malts that were undermodified. These mashes are relatively `thin', so they may be moved
by pumping and can be stirred. Decoction mashing uses three vessels, a stirred mash

mixing vessel, a stirred decoction vessel or mash cooker and a wort separation device,
either a lauter tun or a mash filter. In one traditional mashing programme the grist is
mashed in to give an initial temperature of around 35 ëC (96 ëF). After a stand a decoction
is carried out, that is, a proportion of the mash, e.g., a third, is pumped to the mash
cooker, where it is heated to boiling. The boiling mash is pumped back to the mash
mixing vessel and is mixed with the vessels contents, raising the temperature to, e.g.,
50 ëC (122 ëF). After another stand a second decoction is carried out, increasing the
temperature of the mixed mash to about 65 ëC (149 ëF). A final decoction increases the
mash temperature to about 76 ëC (167 ëF). The mash is then transferred to a lauter tun or a
mash filter. The sweet wort and spargings are collected, ready to be boiled with hops.
Typically, double-mashing uses nitrogen- (`protein-') and enzyme-rich malts and
substantial quantities of maize or rice grits. It also involves the use of three vessels. Most
of the malt g rist is mashed into a mash-mi xing vessel to give a mash at around 38 ëC
1 An outline of brewing 3
(100.4 ëF). The grits, mixed with a small proportion of ground malt and/or a preparation
of microbial enzymes, are mashed in a separate vessel called a cereal cooker. The
contents are carefully heated with mixing, and a rest at about 70 ëC (158 ëF), to 100 ëC
(212 ëF) to disperse the starch and partly liquefy it. The adjunct mash is pumped from the
cereal cooker into the malt mash, with continuous mixing, to give a final temperature of
about 70 ëC (158 ëF). After a stand the mash is heated to about 73 ëC (163.4 ëF), then it is
usually transferred to a lauter tun for wort collection.
Temperature-programmed infusion mashing is increasingly displacing older mashing
systems. The grist is finely ground and the mash is made `thin' to allow it to be stirred.
The grist is mashed into a stirred and externally heated mash-mixing vessel to give an
initial temperature of 35 ëC (95 ëF) for a poorly modified malt or 50 ëC (122 ëF), or more,
for a better modified malt. The mash is heated, with `stands' typically at 50 ëC (122 ëF),
65 ëC (149 ëF) and 75 ëC (167 ëC). Then the sweet wort is collected using a lauter tun or a
mash filter.
1.7 The hop-boil and copper adjuncts
The sweet wort is transferred to a vessel, a copper or kettle, in which it is boiled with hops

or hop preparations, usually for 1±2 hours. Hops are the female cones of hop plants. They
may be used whole, or ground up, or as pellets or as extracts. The choice dictates the type
of equipment used in the next stage of brewing. Pelleted powders are often preferred. Hops
contribute various groups of substances to the wort. During boiling a number of changes
occur in the wort of which the more obvious are the coagulation of protein as `hot break' or
`trub', the gaining of bitterness and hop aroma and the destruction of micro-organisms
(Chapters 9 and 10). Evaporation of the wort, reduces the volume by, say, 7±10%, and so it
is concentrated. Unwanted flavour-rich and aromatic volatile substances are removed.
When used, sugars, syrups and even malt extracts (copper adjuncts) are dispersed and
dissolve in the wort during the copper boil. During the boil flavour changes and a
darkening of the colour occurs. Caramels may be added at this stage to adjust the colour.
The hop-boil consumes about half of the energy use in brewing.
1.8 Wort clarification, cooling and aeration
At the end of the boil the transparent, or `bright' wor t contains flocs of trub (the hot
break) and suspended fragments of hops. If whole hops were used then residual solids are
strained off in a hop back or other filtration device and the bed of hop cones filters off the
trub, giving a clear, hopped wort. However, if powders, hop pellets, (which break up into
small particles), or extracts were used then hop fragments (if present) and the trub are
usually separated in a `w hirlpool tank'. The clear `hopped wort' is cooled to check
continuing darkening and flavour changes and so it can be inoculated (`pitched') with
yeast, and can be aerated or oxygenated without a risk of oxidative deterioration. The
heated cooling water is used for various purposes around the brewery. During cooling a
second separation of solids occurs in the wort. This `cold break' is composed mostly of
proteins and polyphenols and some associated lipids. It is often, but not always,
considered desirable to remove this material to give a `bright', completely clear wort. The
wort is aerated or even oxygenated, to provide oxygen for the yeast in the initial stages of
fermentation.
4 Brewing: science and practice
1.9 Fermentation
Fermentation may be carried out in many different types of vessel (Chapter 14; Boulton

and Quain, 2001). Fermenters may be open or completely closed or they may allow part
of the yeast to be exposed to the air for part of the fermentation period. The variety of
fermenters remains because yeasts working in dif ferent vessels produce beers with
different flavours. Wort fermentation is initiated by pitching (in oculating) the cooled,
hopped wort with a selected yeast. In a few cases mixtu res of yeasts are used. Brewery
yeast is a mass of tiny, single, ovoid cells (Saccharomyces cerevisiae, the `sugar fungus
of beer'). Yeast strains vary in their properties and the flavours they impart. In a very few
cases, as with Belgian Gueuze and Lambic beers, (or some African beers; Chapter 16),
fermentation occurs `spontaneously' and a complex mixture of microbes is involved. The
yeast metabolizes extract substances dissolved in the wort. More yeast cells and `minor'
amounts of many substances are produced, some of which add to the beer's character.
The major products of carbohydrate metabolism are ethyl alcohol (ethanol), carbon
dioxide and heat. The yeast multiplies around 3±5 times. Some is retained for use in
subsequent fermentations, while the surplus is disposed of to distillers or the makers of
yeast extracts.
Traditionally, ales are fermented with `top yeasts' which rise to the top of the beer in
the head of foam. These are pitched at about 16 ëC (61 ëF) and fermentati on is carried out
at 15À20 ëC (59À68 ëF) for 2±3 days. Traditional lagers are fermented with `bottom
yeasts', which settle to the base of the fermenter. These are pitched at lower temperatures
(e.g., 7À10 ëC; 44.6À50 ëF) and fermentations are also carried out at lower temperatures
(e.g., 10À15 ëC; 50À59 ëF), consequently they take longer than ale fermentations. As
wort is converted into beer the removal of materials (especially sugars) from solution and
the appearance of ethanol both contribute to the decline in specific gravity. The initial or
original gravity, OG, the final or present gravity at the end of the fermentation, FG or PG,
and the final alcohol content, are important characteristics of beers.
Yeasts are selected with reference to:
1. their rat e and extent of growth
2. the rate and extent of fermentation
3. the flavour and aroma of the beer produced
4. in older fermentation systems it is imperative that top yeasts rise into a good head of

foam and bottom yeasts sediment cleanly.
Subs tances (finings) may be add ed to promote yeast sep aration at the end of
fermentation. However, in some modern systems `powdery' yeasts are employed that
stay in suspension until the beer is chilled or until collected by centrifugation.
1.10 The processing of beer
When the main, or `primary' fermenta tion is nearly complete the yeast density is reduced
to a pre-det ermined value. The `green' or immature beer (it is not green in colour, but has
an unacceptable, `immature' flavour) is held for a period of maturation or secondary
fermentation. During this process the flavour of the mature beer is refined. Sometimes
`priming' sugar or a small amount of wort is added to boost yeast metabolism and the
`maturation', `conditioning' or `lagering' process. (Lagern is German and means stored
or deposited). In traditional lager b rewing the immature beer was stored cold, e.g., at
1 An outline of brewing 5