Amylases are widespread in nature, and, as well as plants, they are found in animals and are produced by many microbes. Once the endosperm cell walls have been breached and starch granules have been ruptured (both of these events are the result of enzyme activity), starch is available for degradation. In cereals, the mixture of enzymes responsible for partially or totally degrading starch is called diastase. See diastase. This complex mixture does not have a precise composition, and diastase from a raw grain will be different from that after it has been malted. Most of the activity of diastase can be attributed to the activities of two enzymes, alpha and beta amylase, and, to a lesser extent, gamma amylase (together, the amylases), although many other enzymes are also present.

In the brewery mash tun, most starch degradation is the result of amylase activity, but in vivo, for example, in a barley plant, other enzymes will be involved as well. The concerted action of the amylases produces mainly maltose, but it leaves detectable amounts of undegraded dextrins. A pH-promoting general amylase activity is around 5.3. See dextrins.

Diastase was the first enzyme to be isolated, albeit in an impure state, by Persoz and Payen in 1832. It was obtained by precipitating the enzyme out from an extract of malt with ethanol. It came out as a yellowish, amorphous, tasteless powder, and it was found to be able to break down starch, first into dextrins and then into the disaccharide maltose. In the brewhouse, diastase activity in malt is measured as diastatic power and the units of measurement are in °Lintner (°L). See diastatic power.

Barley contains appreciable levels of latent beta amylase (glucan 1,4-alpha maltohydrolase), which is located in the endosperm. During malting the enzyme becomes active and starts to degrade starch slowly, a process that continues in the mash tun. In the absence of other enzymes, beta amylase is unable to degrade starch granules. It is, however, able to carry out (effect) a stepwise attack on amylose, dextrins, and soluble starch chains in solution.

In barley, beta amylase occurs in “free” (soluble) and “bound” (latent, or insoluble) forms. The latter is attached to insoluble proteins through disulfide linkages. When malting, during the steeping of grain, the level of free beta amylase can fall, but during subsequent germination, nearly all of the beta amylase becomes free and the bound form disappears.

Barley does not contain alpha amylase (glucan 1,4-glucanohydrolase), but this enzyme develops in the grain during malting and then gets to do most of its work in the mash tun. Copious quantities of alpha amylase are synthesized in the aleurone layer that surrounds the endosperm.

Synthesis is a response to gibberellic acids secreted by the embryo, and much of the alpha amylase is then secreted into the endosperm. Alpha amylase is an endo-acting enzyme (endoglucanase) in malt and catalyzes the hydrolysis of internal alpha 1,4-glycosidic bonds at random within the starch molecule. Such an attack is slower on short-chain dextrins, is slower near the chain ends, and does not occur in the vicinity of alpha(1→6) branch points. Isoenzymes of alpha amylase are known and have been much studied. Parallel with the formation of alpha amylase during malting is the formation of limit dextrinase, which can hydrolyse the alpha 1,6 linkages in dextrins.

Thus, unlike beta amylase, alpha amylase acting alone can attack starch granules and will steadily degrade them to a complex of sugars (including dextrose), maltose, oligosaccharides, and dextrins during mashing. Alpha amylase requires calcium ions (Ca²⁺) for activity, and, if necessary, the brewer can add gypsum (calcium sulfate, CaSO₄) to the mash tun to ensure a sufficient presence of this cation. Both alpha and beta amylases from malt are active during mashing, although the latter is more heat labile and will not survive very long at elevated temperatures.

Alpha amylase (known to zoologists as ptyalin) is, of course, found in human saliva, where it will break down ingested starches to dextrins and, eventually, maltose. Ptyalin is inactivated by the low pH of gastric juices in the stomach. The enzyme has played an important role in the evolution of beer because, to initiate fermentation, many ancient indigenous peoples would chew their starch- containing raw material and then expectorate the bolus into a vessel intended for fermentation. Via this simple method, fermentable material could be obtained for brewing purposes.

The practice of prechewing grain for subsequent feeding to infants, the sick, or the elderly developed many moons ago, and the use of saliva to hydrolyze starch was likely the original way of initiating fermentation. Perhaps the classic example of this is chicha, a beverage of many South American native tribes. See chicha. Indeed, it is thought that the very name of this drink emanates from “chichal,” a word that translates as “with saliva” or “to spit.” Most chicha was made from the indigenous crops manioc and/or maize (the latter mainly in regions conquered by the Incas). Chewing was the only means of imparting amylolytic enzymes into manioc root.

See also alpha amylase, malting, mashing, and wort.