Uk

Top fermented

Highly bittered strong bottled pale ale originally brewed for export to British troops in India

Kölschbier

Köln (Cologne) Germany

Top fermented

Pale golden highly hopped ale with acidic/ lactic taste (4.6% abv)

Mild ale

North and Midlands, England

Top fermented

Lightly-hopped, sweet, dark brown ale (3.54.0% abv)

Fermentation system Characteristics

Table 2.1 Contd Beer

Weizenbier

Blanche de Hoegaarden Lambic

Gueze

Porter Provisie

Rauchbier (smoked beer)

Saison Scotch ale

Steam beer Stout

Trappist beers

Origin

Bavaria, Germany

Flanders, Belgium Brussels area, Belgium

Brussels area, Belgium

London, UK

Oudenaarde, Belgium

Bamberg, Bavaria, Germany

Walloon region of Belgium

Scotland, UK

California, USA

Sweet stout (UK) Dry stout (Eire)

Five brewing abbeys of Belgium (Chimay, Orval, Rochefort, St Sixtus, Westmalle) and one remaining in Holland (Schaapskooi)

Top fermented

Top fermentation

Spontaneous top fermentation

Bottle fermented

Top fermented

Top fermented

Bottom fermented

Top fermented

Bottom fermented, low fermentation temperature

Top fermentation using bottom yeast at relatively high temperature

Top fermentation

Mainly top fermentation; the Dutch brewery produces a bottom fermented Pilsener-type lager as well

Lightly hopped, highly carbonated wheat beer with estery, phenolic taste. Usually bottle conditioned (5-5.5% abv)

Wheat beer from 50% wheat and 50% malt Wheat/barley beer with sour or estery flavour depending on age Blend of young and old iambic, bottle fermented and aged for at least a year. Dry, fruity and highly carbonated (5-5.5% abv)

Deep ruby colour from brown malts and made with London water, high in bicarbonate (67% abv) Sweet dark ale aged for a minimum of 2 years and up to 25 years (5.5-6.5% abv) Dark beer with smoked taste due to practice of drying malts over open beech wood fires Estery amber-coloured bottle conditioned ale (5.5-6.0% abv) Dark copper brown, strong sweet ale with creamy taste (7-10% abv)

Well-hopped amber coloured highly carbonated beer (sound of gas escaping from broached casks gives name). (4.5-5.0% abv)

Very dark, highly hopped made with up to 10% roasted unmalted barley and possibly caramel malt. Dry version (Guinness) more alcoholic (4.05.0% abv) Brown or amber colour, bottle conditioned. Usually several beers of different strengths produced (5-12% abv)

goal of fermentation technologists has been to identify more rapid maturation procedures. This has been successful to the point that most lager beer is now produced by a process which takes days as opposed to months to complete. The only certain way of distinguishing lagers made by a traditional process from their counterparts made by foreshortened modern processes is by knowledge of specific brands made at breweries where the plant and process are known.

This highlights another aspect of beer classification, particularly those with a long heritage. This is the practice of naming beer styles after the region of their origin. There are numerous examples including 'London porter', 'Pilsener' (from Plzen, Bohemia in the Czech Republic), 'Miinchener' (Munich, Germany) and 'Dortmunder' (Dortmund, Germany). These beers have distinctive characters and the original versions are produced using traditional processes. They owe their geographical origins to several factors, especially local availability of a particular combination of raw materials that lend themselves to the type of beer being produced. In addition, the mineral composition of the local water supply was usually a crucial influence.

Derivative versions of these classic beer styles are now brewed worldwide, arguably not always with great success. The example par excellence of an exported beer style is the pale Pilsener type lager which is now the most commonly brewed international beer style. Beers of this variety frequently have the word 'Pils' attached to the brand name. They are now brewed using a large range of techniques ranging from the traditional low-temperature fermentation and long maturation phase through to relatively rapid high-temperature fermentations and maturation in a few hours using immobilised yeast reactors. Various sources of fermentable sugars, other than the original malted barley, are used and the mineral content of the brewing water is adjusted so that any local supply is usable. Even zero or low alcohol variants are available.

Ales of the types brewed in the United Kingdom were originally distinguished from beers in that, although both were made from malted barley, ales were not bittered by the addition of hops, whereas beers were. In another sense, ales were considered to be country beers, whereas beer had urban associations. Thus, hops were introduced into the UK probably from Holland and Belgium in the fifteenth century and naturally their spread from the cities of importation to the provinces took longer. By the eighteenth century most ales were hopped but the term was reserved for paler country beers, which were distinct from dark town-brewed beers (Sambrook, 1996). In the modern sense ales have been distinguished from lagers by the use of fermentations employing top-cropping and bottom-cropping yeast strains, respectively. In addition, ales tend to be fermented at higher temperatures than lager beers.

In fact, the march of progress has rendered obsolete many of these points of distinction. Thus, in modern breweries there has been a tendency to use increasingly higher fermentation temperatures for lagers in order to shorten vessel residence times and this distinction between ales and lagers is becoming blurred in many breweries. The production of traditional ales is associated with the use of open shallow fermenting vessels, which facilitate removal of the yeast top crop. However, in many large modern breweries, deep cylindroconical vessels are now used for both ale and lager fermentations. In these cases manipulation of the conditions in the fermenter allow ale yeast strains to form bottom crops in the same manner as lager yeast strains.

It may be appreciated from the foregoing discussion that there are now almost two parallel brewing industries. The first produces a traditional beer using a process which has been almost frozen at a particular point in time. The products devolving from these processes constitute the parental classic beer types. The second industry is derived from the first and is typified by the modern often large-capacity brewing factory. Here the same beer types may be produced but using traditional processes, which have been adapted to afford greater efficiency, or by the introduction of totally new methods for achieving the same end products.

By a process of elimination it may be supposed that the unique points of difference between beer types on the world stage are the raw materials used to make the wort and the nature of the micro-organisms used to catalyse the conversion to beer. The vast majority of beers are made by fermentation of an aqueous extract of malted barley, possibly supplemented with other sources of fermentable sugars. The types and blend of malts used are characteristic for each beer type. In particular, the malt supplies much of the colour of the beer as well as flavour. Thus, Pilsener lager beers are made from pale malts whereas black and chocolate malts are roasted to supply colour and flavour to dark beers such as stouts. Similarly, the varieties, rate and point of addition of hops to beers are characteristic. True Pilsener lager beers are well hopped and traditionally use the renowned Bohemian Saaz variety of hop.

UK cask-conditioned ales use hops in the copper for bittering purposes, possibly supplemented with other aroma hops added to the cask. Traditional varieties include Fuggles and Goldings.

As with process conditions, both sources of fermentable sugars and hop flavourings have been subject to continuous developments. Brewing in Germany is still subject to the Reinheitsgebot, or beer purity laws, which preclude the use of ingredients other than water, malt, hops and yeast. Other countries have less proscriptive legislation and many other sources of fermentable extract are now used. These additional sugars, termed brewing adjuncts, may be obtained from cereals, either malted or unmalted, other crops such as rice or from semi-refined sugar syrups. Similarly, many new varieties of hops are now available and frequently they are used in forms in which the active ingredients have been isolated and rendered into forms which make them easier to dose into beer, or render them into a form in which they have new more desirable properties. It is no longer possible, therefore, to provide a single definitive recipe from which a particular type of beer can be brewed and this represents another way in which specific beer styles have drifted from the original parental type.

Wheat beers are made partially or entirely from malted wheat. Typically they are produced by top fermentation at relatively high temperature. As a group they are lightly hopped and many have a characteristic clove or phenolic flavour. This feature demonstrates the critical influence of the strain of yeast used for fermentation. The clove-like flavour is due to the formation of a group of yeast metabolites, particularly 4-vinyl guaiacol and 4-vinyl phenol via the decarboxylation of /?-coumaric and ferulic acids, respectively, during fermentation. The production of these compounds from precursors, which derive from malted cereals, is under the control of a gene, termed 'POF' for 'phenolic off-flavour' (Section 8.1.3.1). The presence of the POF gene in the yeasts used to make wheat beers is considered beneficial and essential. As the name implies, the formation of these compounds in other beers would be considered a grave flavour defect. Occasionally they may arise by contamination with a so-called wild yeast strain, which carries the POF gene. In this sense the brewer's use of the term wild yeast is similar to that of the gardener who describes a weed as a flower in the wrong place.

This serves to demonstrate that almost without exception the strain or mixture of strains of yeast used to produce a particular type of beer is the single essential component, which cannot be substituted. Undoubtedly yeast strains were selected by accident as being the most suitable for the particular style of beer. Properties of note would include flocculence characteristics, top or bottom cropping, optimum growth temperature and ethanol tolerance. In addition, and perhaps of greatest importance, is the crucial influence of the yeast strain on the development of beer flavour and aroma constituents. Even this aspect of brewing has been subject to change. It has always been common practice to select new strains of yeast from existing populations, which have properties in some way more suitable than the parental type. In recent years, developments in genetic engineering have afforded new opportunities for more directed manipulation of yeast properties, although such altered yeasts have not yet been used at commercial scale.

Not all beers use yeast strains as the sole fermenting agents. In this respect the Belgian Iambic beers, produced in a single area close to Brussels, are unique. The wort is made typically from 40% unmalted wheat and 60% malted barley and contains high concentrations of dextrins. High dosing rates with hops that have already been used for brewing and consequently contain little bittering substances but retain antiseptic properties, are included in the process of wort manufacture. The unique aspect of these beers is that the fermentation is spontaneous. The wort is allowed to cool in large shallow open vessels, which are located in rooms where good ventilation provides the maximum opportunity for contamination with the microbial flora of the room. After holding overnight in the cooling vessel, the wort is transferred to wooden casks where it receives a further natural inoculum. The fermentation takes place over a period of several months in the casks and is typified by successive blooms of several distinct microbial populations.

First, yeasts of the genus Kloeckera and various enteric bacteria grow and produce some acetic acid (Martens et al., 1991). After 2-3 weeks Saccharomyces yeasts overgrow the initial microbial population resulting in the formation of ethanol and some esters. After some 3-4 months, bacteria belonging to the genera Lactobacillus and Pediococcus become predominant, resulting in the formation of much higher concentrations of lactic acid. Finally, after 5-8 months, a further yeast population develops, in this case species of the genus Brettanomyces, typically B. bruxellensis and B. lambicus, producing additional flavour and aroma components (see Section 8.1.3.2).

The Iambic fermentation may last for up to two years. Young Iambic beer may be sold directly from the cask as Iambic doux, or after three years in cask it may be sold as old Iambic vieux. Another variant, faro, is Iambic sweetened by the addition of sugar. More commonly, Iambic of various ages is used as a base to produce other beer types. Thus, Iambic beers of various ages are blended to obtain what is considered a product with a desired balance of flavours, lightly filtered and bottled. The resultant gueuze is subjected to a lengthy secondary fermentation, frequently of two or more years, in bottle to produce carbonation and allow the flavour to mature. Another variation is that in which young Iambic is blended with whole macerated fruit prior to bottling for secondary fermentation. Such beers are named after the fruit used, for example, kriek (cherries), framboise (raspberry), cassis (blackcurrant), pêche (peach) and muscat (grape).

As with other countries, the techniques applied to brewing Iambic beers have undergone some development and modifications to the basic process have been introduced both to improve process efficiency and in response to consumer demand. In this case gueuze is made from a blend of traditional Iambic and a base beer produced by wort fermentation using a cultured mixture of Brettanomyces yeast, Lactobacillus and Acetobacter.

Some new styles of beers have arisen in recent years. Concerns over drinking and health have provided a market for low- or zero-alcohol beers. Low-alcohol beers are not new, for example, the German Malzbier containing 0.5-1.0% abv has a long heritage. Similar beverages, often called 'near beers', are produced in many countries, usually with an alcohol content of less than 0.6% abv. However, these tend to be specific highly flavoured malty beverages sold as tonics for their high nutritive contents. More recently, a market has developed for low or zero alcohol versions of existing beers, in particular, Pilsener-type lagers. Usually there is a legal definition of the alcohol content, typically less than 1.0-2.0% abv for low alcohol and less than 0.05% abv for zero alcohol beers (Davies, 1990).

Several processes have been developed for production of these beers (Muller, 1990; Regan, 1990). These are of two types: first, removal of ethanol from a fully fermented beer; second, manipulation of fermentation conditions to produce a beer with low or zero alcohol content. Both approaches have advantages and disadvantages.

Removal of alcohol from a fully fermented beer may be achieved by vacuum distillation or evaporation, dialysis or reverse osmosis. Distillation and evaporation make use of the high volatility of ethanol compared to other beer components. The use of a vacuum is favoured since it allows comparatively low temperatures (40°C) to be used, thereby, minimising potential flavour perturbations due to thermal damage. A typical single-stage vacuum evaporation system is shown in Fig. 2.1. The beer in-feed is preheated and evaporated and the resultant mixture of beer and vapour fed into a separating column. Here the alcohol vapour is taken off from the top and condensed prior to collection. The de-alcoholised beer is taken from the base of the separator and cooled. With single units the beer is recirculated in order to achieve the desired alcohol content. Multiple units allow a single pass operation, which will reduce ethanol concentrations to less than 0.05% abv, the maximum limit for alcohol-free beers.

Evaporative or distillation processes have the disadvantage that some stripping of flavour volatiles is inevitable. Reverse osmosis and dialysis approaches to de-alcoholisation rely on forcing ethanol across a semi-permeable membrane by generating a pressure differential or by establishing a concentration gradient, respectively. These plants are operated at low temperatures, thereby reducing the risks of heat damage to the beer but they are not practicable methods for achieving very low ethanol concentrations. These methods may also remove desirable flavour components with ethanol.

Steam

Steam

Fig. 2.1 Schematic of plant for production of de-alcoholised beer using vacuum evaporation (redrawn from Regan, 1990).

Manufacture of low or zero alcohol beers by de-alcoholisation allows the brewery to produce a normal strength beer stream from which a desired proportion may be diverted and treated. However, this flexibility is an expensive option in terms of installation and running costs of the de-alcoholisation plant. The other approach is to manage fermentation so as not to produce alcohol in the first place. This may be achieved in several ways but the general guiding principle is that it is necessary to produce beer flavour and aroma components without ethanol formation and to ensure that undesirable wort flavour components are eliminated. Capital cost associated with these methods is low because little if any modification to existing plant is needed.

Muller (1990) discussed a number of approaches that appear superficially feasible, but, as the author points out, lack practicality. For example, fermentation of a very-low-gravity wort either produced specifically for the purpose, or obtained by dilution of normal-gravity wort. These methods fail since insufficient flavour compounds are generated during fermentation. Production of wort using temperatures below 60° C results in very low fermentability due to lack of gelatinisation and hydrolysis of starches. However, malt flavour components may still be extracted. In practice, runoff rates are unacceptably low because of the presence of starch. Similarly, arresting a standard gravity fermentation at a point where ethanol concentration is low is also unsatisfactory because undesirable wort carbonyls are still present.

A more promising method is dilution of very-high-gravity (1080) beers. In this instance the increased formation of flavour volatiles associated with very-high-gravity brewing (see Section 2.5) is corrected for by post-fermentation dilution to a low ethanol concentration. Pilot scale production of low alcohol beers using this method was described by Muller (1990). A significant concentration of esters and higher alcohols was achieved in a beer with an alcohol content of less than 2% abv. However, foam performance was very poor, an effect attributed to over-dilution of the available total soluble nitrogen.

Another way of producing wort with low fermentability is to perform the mashing step at a high temperature. Here the premise is that degradation of starches by a-amylases produces small quantities of fermentable sugars together with high concentrations of non-fermentable dextrins. Conversely, ß-amylases produce mostly fermentable sugars in the form of maltose, ß-amylases are less heat stable than a-amylases and thus, use of a high mashing temperature (80-85°C) produces a wort with sufficiently low fermentability to give a low alcohol product. This method has been used successfully at commercial scale. It requires very accurate control of mashing temperature since if this is too low fermentability increases, if too high the wort will have an elevated starch content.

The most often used limited fermentation approach is the cold contact method in which wort is exposed to yeast for a brief period at low temperature and under anaerobic conditions. This treatment precludes yeast growth and ethanol formation but permits removal of wort carbonyls. This method is particularly suited to a continuous process using immobilised yeast reactors and it is in this form that it has found successful commercial application (see Section 5.7.2.1).

Another comparatively modern development in beer styles is the so-called diet, low-carbohydrate or light ('lite') beers. These are fermented so that there is little or no residual gravity. This is achieved by producing worts in which dextrin contents have been reduced by addition of amyloglucosidase. Alternatively, super-attenuating yeast strains may be used which possess amyloglucosidase activity. Several authors have described construction of such yeast strains using genetic engineering techniques although none has been used for commercial brewing (Lancashire et al., 1989; Vakeria & Hinchliffe, 1989; Hansen et al., 1990).

These beers are suitable for diabetics because of their low carbohydrate content and it was to meet this need for which they owe their German origin, where they are known as Diätbier or Diät Pils. Occasionally and incorrectly, they may be referred to as low-calorie beers. Obviously conversion of dextrins to fermentable sugars enhances ethanol formation and this is not inconsiderably calorific. In order to be a truly low-calorie beer it is necessary to reduce both carbohydrates and ethanol.

2.2.1 Beverages related to beer

As discussed in Chapter 1 there are many alcoholic beverages that may be categorised as beers in that the principal source of fermentable sugar is a grain but which are obviously distinct from the European beer tradition. There are numerous examples of such beers as described in Table 1.1. Two members of this group are worthy of further discussion since they are of considerable commercial importance: saké and sorghum beer.

2.2.1.1 Saké. Excellent reviews of the nature of saké and full details of its production may be found in Kodama (1970, 1993) and Inoue et al. (1992a). It is a beer-

type beverage produced by fermentation of sugars derived from rice and typically contains 14-17% alcohol by volume. It is clear, pale yellow, has both sweet and acidic flavour notes and an estery aroma. Saké is the national drink of Japan, although it probably originated in China. It is still made in the latter country although the Japanese and Chinese processes have now diverged. Japanese saké is fermented using specific yeast strains and the mould Aspergillus oryzae. Chinese saké is prepared using a microbial flora which develops spontaneously and contains yeasts as well as various moulds belonging to the genera Rhizopus, Mucor, Pénicillium, Absidia and Monascus, in addition to A. oryzae (Kodama, 1993).

As with conventional beer brewing, saké can be made using a traditional process, which is highly labour-intensive. However, modern automated alternatives to many of the steps have now been introduced. The mould, A. oryzae provides amylases and proteases to release sugars and amino nitrogen from the rice grains.

Large grain rice varieties are used and these are first pre-treated using a mechanical milling treatment to remove the bran. This treatment removes much of the rice protein and lipids, both of which are considered undesirable. The proportion of bran removed, on a weight basis, compared to the remaining grain is termed the polishing ratio. After the polishing treatment the rice is washed then steeped in water. Steeped rice is then steamed to gelatinise starch and denature proteins. After cooling the steeped rice is inoculated with a culture of A. oryzae in the form of a dried mass of mould, rich in spores and rice, known as tane-koji. The mould proliferates on the wet rice covering it in a mycelium, which penetrates into each grain. This mixture is known as rice-koji.

For the main fermentation a starter culture is prepared, known as moto ('mother of saké'). In the traditional process a mixture of steamed rice, water and ric e-koji is prepared and held for a period for saccharification to occur. During this time a complex bloom of bacteria and yeast develops then dies off. This is accompanied by the formation of lactic acid. At this point the infusion is inoculated with a pure culture of saké yeast (Saccharomyces cerevisiae var. sake). This yeast has the important characteristic of being highly ethanol tolerant. The mixture is held for a number of days during which rapid yeast growth takes place. The moto is used as the starter culture for the main fermentation, or moromi.

The moromi fermentation is conducted in large open vessels in which sequential batches of steamed rice, water and ric e-koji are added to the moto starter. The batch addition process maintains a high yeast concentration and reduces the risk of contamination. The fermentation takes roughly two weeks, during which time the ethanol concentration increases to approximately 17-20% by volume. At this point flavour adjustments may be made by addition of lactic and succinic acids, glucose and sodium glutamate. Ethanol may also be added to achieve a final concentration of 2022%. The process is completed by allowing solids to sediment and clarifying the liquid by filtration. Following a sometimes lengthy maturation storage phase, the saké is pasteurised and bottled.

2.2.1.2 Sorghum beer. Sorghum beer is the traditional native alcoholic beverage of South Africa. Similar beers are associated with several African countries and many names may be used, for example, joala (Sesotho), utshwala (Zulu) and utywala

(Eastern Cape tribes) (van Heerden, 1989). The modern version is called sorghum, Bantu or opaque beer. It has a long heritage and in its many guises a variety of sources of fermentable sugars other than sorghum may be used, for example, maize, millet, cassava and malted barley. Three scales of production are currently in operation: within a tribal context, as an urban domestic undertaking and at commercial brewery scale (Novellie & de Schaepdrijver, 1986).

Sorghum beer is described as being opaque, slightly viscous, usually with a pink tinge and sour tasting. When sold in unpasteurised form sorghum beer may be still slowly fermenting when consumed. The industrial product is now made in a commercial brewery using stainless steel plant. Batch sizes are modest, typically 1000020000 litres.

The beer is made from malted sorghum and an adjunct which is usually maize but can be other cereals, including unmalted sorghum. In the first stage a sorghum malt flour is prepared which is suspended in water at a temperature of 48-50°C. This is inoculated with a culture of Lactobacillus leichmanii and a souring process takes place in which lactic acid is formed. The relatively high temperature helps prevent growth of other micro-organisms. Furthermore, little sugar is formed since the acid conditions inhibit sorghum amylases. When sufficient lactic acid is judged to have been generated (approximately pH 3.2) more water is added, together with maize adjunct and the mixture heated to boiling point to gelatinise starch and soften the maize.

After cooling to 60°C, further sorghum malt is added and saccharification takes place due to the amylases present in the sorghum malt. The wort so formed is then clarified by passing the process stream through in- line centrifugal decanters. This part of the process is termed straining, a reference to an earlier method of accomplishing this separation. The fermentation is started by the addition of a dried yeast culture (see Section 7.1.1.3), is conducted at relatively high temperature and is rapid.

In modern plants the beer may be pasteurised and bottled with added sugar and yeast to allow for secondary fermentation, mainly for carbonation. More usually it is sold still fermenting in draught form or in plastic-coated cartons of various capacities and which are fitted with vented closures.

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