Brewing Enzymes

Traditionally, beer is produced by mixing crushed barley malt and hot water in a large circular vessel called a mash copper. This process is called mashing. Besides malt, other starchy cereals such as maize, sorghum, rice and barley, or pure starch itself, are added to the mash. These are known as adjuncts. After mashing, the mash is filtered in a lauter tun. The resulting liquid, known as sweet wort, is then run off to the copper, where it is boiled with hops. The hopped wort is cooled and transferred to the fermentation vessels, where yeast is added. After fermentation, the so-called 'green beer' is matured before final filtration and bottling. This is a muchsimplified account of how beer is made. A closer look reveals the importance of enzymes in the brewing process. The traditional source of enzymes used for the conversion of cereals into beer is barley malt, one of the key ingredients in brewing. If too little enzyme activity is present in the mash, there will be several undesirable consequences: the extract yield will be too low; wort separation will take too long; the fermentation process will be too slow; too little alcohol will be produced; the beer filtration rate will be reduced; and the flavour and stability of the beer will be inferior.

Industrial enzymes are used to supplement the malt's own enzymes in order to prevent these problems. Furthermore, industrial enzymes can be used to ensure better adjunct liquefaction, to produce low-carbohydrate beer ('light beer'), to shorten the beer maturation time, and to produce beer from cheaper raw materials.

Malt is the traditional source of alpha-amylase for the liquefactionof adjuncts. The action of alpha-amylase ensures simpler liquefaction and shorter process times. Heat-stable alpha-amylase preparations (e.g. AETLs' SEBstal HTL) are becoming more popular for three main reasons:

• They enable a more predictable and simpler production process. As heat-stable amylases are much more stable than malt amylases, simpler liquefaction, shorter process times and an overall increase in productivity can be achieved.
  
• The malt enzymes are preserved for the saccharification process, where they can be used to better effect. This safeguards the brewhouse operation and results in a better wort and, ultimately, a better beer.
  
• Eliminating the malt from the adjunct cooker means less adjunct mash and thus more freedom in balancing volumes and temperatures in the mashing programme - a problem for many brewers who use a high adjunct ratio.

Traditionally, the use of barley has been limited to 10-20% of the grist when using high-quality malts. At higher levels or with low-quality malts, processing becomes more difficult. In these cases the mash needs to be supplemented with extra enzyme activity if the brewer is to benefit from the advantages of using unmalted barley while still maintaining brewing performance. Brewers can either add a malt-equivalent blend of alpha amylase, beta-glucanase and protease (SEBmalt Plus of AETL) at the mashing-in stage or add the enzymes separately as required.

Wort separation and beer filtration are two common bottlenecks in brewing. Poor lautering not only reduces production capacity but can also lead to lower extract yields. Furthermore, slow lautering negatively affects the quality of the wort, which may lead to problems with filtering the beer, and with the flavour and stability of the beer. A thorough breakdown of beta-glucans and pentosans during mashing is essential for fast wort separation. Nondegraded beta-glucans and pentosans carried over into the fermenter reduce the beer filtration capacity and increase the consumption of diatomaceous earth (kieselguhr). A wide range of beta-glucanase/pentosanase or Proganozyme of AETL is for use in mashing or fermentation/maturation are available to solve these problems.

Small adjustments in fermentability can be achieved byadding a fungal alpha-amylase at the start of fermentation or by adding a debranching enzyme (Multizyme of AETL) together with a glucoamylase at mashing-in. Beer types with very high attenuation (light beer) can be produced using saccharifying enzymes. Fungal alpha-amylases are used to produce mainly maltose and dextrins, whereas glucoamylase produces glucose from both linear and branched dextrins. The alcohol content is another parameter that brewers are interested in controlling. The amount of alcohol in a beer is limited by the amount of solids (extract) transferred from the raw materials to the wort, and by the level of fermentable sugar in the extract. In turn, the sugar content is controlled by the amount of starch degradation catalysed by the amylases in the mash, and by the saccharifying enzymes used during fermentation.

When exactly is a beer mature? This is an important question for brewers because it determines when they can 'rack' the beer to make way for the next batch. The simple answer to the above question is when the diacetyl level drops below a certain limit (about 0.07 ppm). Diacetyl gives beer an offflavour like buttermilk and one of the main reasons for maturing a beer is to allow the diacetyl to drop to a level at which it cannot be tasted. Diacetyl is formed by the non-enzymatic oxidative decarboxylation of alpha-acetolactate, which is produced by the yeast during primary fermentation. The diacetyl is removed again by the yeast during the beer maturation stage by conversion to acetoin, which has a much higher flavour threshold value.In fact, acetoin is almost tasteless compared with diacetyl. By adding the enzyme alpha-acetolactate decarboxylase (e.g. AETLs' SEBMature) at the beginning of the primary fermentation process, it is possible to bypass the diacetyl step and convert alpha-acetolactate directly into acetoin.