Enzymes are complex organic substances that act as catalysts: that is they accelerate the velocity of a reaction whilst remaining essentially unchanged themselves at the end of it. They promote the hydrolysis of proteins and polysaccharides into simpler substances, and are usually highly specific. Each enzyme will act on only a limited range of substrates, frequently on only one.
The main factors affecting enzyme activity are temperature and pH, and to a lesser extent Calcium, moisture and oxygen. An increase in temperature increases the rate of reaction up to an optimum that varies from enzyme to enzyme. Above that optimum temperature the enzyme is destroyed. Individual enzymes also have variable optimum pH ranges. Their activity is optimised within this range, and inhibited at pH values above and below this range. Enzymes will normally be destroyed at pH values far removed from the optimum range. During the germination stage of malting the formation of many enzymes is promoted and is dependent upon the moisture and oxygen content of the barley. In the mash, Calcium is essential for the stabilisation of a-amylase, one of the most important enzymes in the brewing process. Without the protection of Calcium ions a-amylase is rapidly destroyed at normal mashing temperatures. When Calcium is present in sufficient amounts the enzyme is stable at above sparging temperatures, only then being finally destroyed in the Copper.
Much enzyme activity is started in the maltings. The barley is steeped to increase the moisture content to 42 – 46% and oxygenated to promote enzyme activity in the aleurone layer, all under controlled temperature conditions. The barley is then allowed to germinate when modification of the the barley to malt occurs.
Enzymes such as ß-amylase, exo-peptidase and carboxy-peptidase are present in the starchy endosperm of the barley, and are activated during malting. Other enzymes, such as ß-glucanase, endo-proteases, a-amylase and pentosanases are formed in the aleurone layer of the barley during malting. The formation and activation of these enzymes is promoted by the increasing moisture and oxygen during the steep, and is then arrested by the kilning. Good kilning should put the enzymes into ‘suspended animation’ until they are re-activated in the early stages of the mash, rather than destroying them.
ß-glucanases are highly active during this germination period, breaking down ß-glucan (cell wall material) into simpler substances. ß-glucanase is highly heat labile, and survives for only a very short time at mashing temperatures. It is therefore essential to get as much ß-glucan broken down during malting as possible, since it will cause problems later in the process by increasing viscosity and wort run-off times and by causing hazes.
The protein specific enzymes, exo-proteases and endo amino-peptidases are again highly heat labile, and work mainly in the malt-house. Carboxy-peptidases are a little less heat sensitive, and may continue to operate for as little while in the mash.
The optimum pH range for ß-glucanase and proteases is in the order of 5·0 – 5·5, and temperature range of 35 – 45° C is optimum. These enzymes then are quickly destroyed in the mash when using an infusion mash at 63 – 66° C. However when using decoction mashing techniques and a much reduced initial mash temperature, significant enzyme activity can occur in the early stages of mashing. It is for this reason that malts for use in decoction mashing systems need not be so well modified as those for use in infusion mashes.
The usual mashing temperature for British beers of 63 – 65° C is as a result of the optimum temperature for the activities of alpha & ß-amylase, 64 – 68° and 60 – 65° C respectively. Both are highly active within the normal pH range of wort, 5·2 – 5·5, and the exact temperature of mash selected by the individual brewer will determine whether the alpha or ß-amylase activity is favoured during the mash. Calcium ions are required to stabilise the activity of alpha-amylase, which is an endo-enzyme, cleaving internal a-1, 4-glucosidic links of gelatinised starch. Alternatively ß-amylase, which does not require calcium for stabilisation, is an exo-enzyme, cleaving external a-1, 4-glucosidic links to form maltose and ß-limit dextrins. The latter contain a 1, 6-glucosidic link, and cannot be cleaved by either alpha or ß-amylase, and so remain in the wort through fermentation as non-fermentable sugars (Dextrins). The natural enzyme produced in the wort that will cleave this link is limit dextrinase, but this is highly heat labile and is destroyed completely at mashing temperatures.
The use of additional enzymes is common throughout the brewing industry, and is greatly beneficial. ß-glucanase is possibly the most common addition, assisting as it does the mashing of grists containing under modified or unevenly modified corns. It aids Mash Tun run off by reducing wort viscosity, also improving subsequent beer fineability and filterability. Amylases are also used, typically where the use of adjuncts may dilute the availability of enzymes in the Mash Tun.
Enzyme cocktails, such as Trizyme are formulated to address a range of Mash Tun problems. Use of these products will increase extract, reduce wort viscosity and run-off times, lead to a brighter wort ex Copper and improve beer fining performance and head retention.
It is possible, if required, to reduce the amount of dextrins remaining in the beer as non-fermentable sugars by the addition of Amylo-Glucosidase, AMG. This enzyme is used in the Mash Tun and will cleave the 1,6-glucosidic bond to produce glucose. This enzyme finds favour in the production of high alcohol or low carbohydrate beers. One drawback is that the enzyme is not destroyed at pasteurisation temperatures and will therefore continue to work in package.
Enzymes are also used in the brewing process post-fermentation, to control chill-haze in packaged beers and increase shelf-life. Such enzymes are proteolytic based on papain (Carica Papaya) and have an optimum temperature range of 35 – 45°C, and pH range of 4 – 5·5. Added to conditioning tank they will break down the high molecular weight proteins that react with polypeptides to form chill hazes. Whilst other means of inhibiting chill haze are available – for example the use of Silica Hydrogel or PVPP – Papain remains one of the most cost effective and widespread means of achieving this objective.