Brewing

Science and Practice

D E Briggs, P A Brookes, R Stevens, C A Boulton

• Publisher: Woodhead Publishing
• Year: 2004
• ISBN:
  9781855739062
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Brewing is one of the oldest and most complex technologies in food and beverage processing. Its success depends on blending a sound understanding of the science involved with an equally clear grasp of the practicalities of production. Brewing: science and practice provides a comprehensive and authoritative guide to both of these aspects of the subject.After an initial overview of the brewing process, malts, adjuncts and enzymes are reviewed. A chapter is then devoted to water, effluents and wastes. There follows a group of chapters on the science and technology of mashing, including grist preparation. The next two chapters discuss hops, and are followed by chapters on wort boiling, clarification and aeration. Three chapters are devoted to the important topics of yeast biology, metabolism and growth. Fermentation, fermentation technologies and beer maturation are then reviewed, followed by a consideration of native African beers. After a discussion of brewhouses, the authors consider a number of safety and quality issues, including beer microbiology and the chemical and physical properties of beer, which contribute to qualities such as flavour. A final group of chapters cover packaging, storage, distribution and the retail handling of beer.Based on the authors' unrivalled experience in the field, Brewing: science and practice is a standard work for the industry.

• A detailed account of all stages of the brewing process
• Safety and quality issues are discussed, including the chemical and physical properties of beer and beer microbiology
• A strong partnership of the science and the practicalities of production ensures this book is a primary reference

1

An outline of brewing

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 (h1) a week to thousands of h1. 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 is reduced. When germination and 'modification' are sufficiently advanced they are stopped by kilning. The 'green malt' (green in the sense of immature, 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 forbidden. 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 systems 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. 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 will 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 (especially 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 isothermal, infusion mashing system, (traditional for British ale brewers); (b) the decoction system, (traditional for mainland European lager 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 predetermined 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 mashing 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 63–67 °C (145.4–152.6 °F). 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 75–80 °C (167–176 °F ) 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 °C (96 °F). 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 °C (122 °F). After another stand a second decoction is carried out, increasing the temperature of the mixed mash to about 65 °C (149 °F). A final decoction increases the mash temperature to about 76 °C (167 °F). 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 grist is mashed into a mash-mixing vessel to give a mash at around 38 °C (100.4 °F). 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 °C (158 °F), to 100 °C (212 °F) 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 °C (158 °F). After a stand the mash is heated to about 73 °C (163.4 °F), 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 °C (95 °F) for a poorly modified malt or 50 °C (122 °F), or more, for a better modified malt. The mash is heated, with 'stands' typically at 50 °C (122 °F), 65 °C (149 °F) and 75 °C (167 °C). 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' wort 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 'whirlpool 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.

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 different vessels produce beers with different flavours. Wort fermentation is initiated by pitching (inoculating) the cooled, hopped wort with a selected yeast. In a few cases mixtures 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 °C (61 °F) and fermentation is carried out at 15–20 °C (59–68 °F) for 2–3 days. Traditional lagers are fermented with 'bottom yeasts', which settle to the base of th...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Preface
• 1: An outline of brewing
• 2: Malts, adjuncts and supplementary enzymes
• 3: Water, effluents and wastes
• 4: The science of mashing
• 5: The preparation of grists
• 6: Mashing technology
• 7: Hops
• 8: The chemistry of hop constituents
• 9: Chemistry of wort boiling
• 10: Wort boiling clarification, cooling and aeration
• 11: Yeast biology
• 12: Metabolism of wort by yeast
• 13: Yeast growth
• 14: Fermentation technologies
• 15: Beer maturation and treatments
• 16: Native African beers
• 17: Microbiology
• 18: Brewhouses: types, control and economy
• 19: Chemical and physical properties of beer
• 20: Beer flavour sensory assessment
• 21: Packaging
• 22: Storage and distribution
• 23: Beer in the trade
• Appendix: units and some data of use in brewing
• Index