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Mashing

Mashing is the process of converting starch from the milled malt and solid adjuncts into fermentable and unfermentable sugars to produce wort of the desired composition. The composition of the wort will vary according to the style of beer. Mashing involves mixing milled malt and solid adjuncts with water at a set temperature and volume to continue the biochemical changes initiated during the malting process.

The mashing process is conducted over a period of time at various temperatures in order to activate the enzymes responsible for the acidulation of the mash (traditionally for lagers) and the reduction in proteins and carbohydrates. Enzymes are biological catalysts responsible for initiating specific chemical reactions. Although there are numerous enzymes present in the mash, each with a specific role to play, this discussion is limited to the three principal groups and their respective processes. These enzymes are 1) phytases (acidifying), 2) proteolytic enzymes (protein-degrading), and 3) carbohydrase enzymes (starch-degrading).

The acid rest is responsible for reducing the initial mash pH for traditional decoction mashing of lager beers. In recent years, because of the use of well-modified malts, the general trend has been to simplify and shorten the lager mash by eliminating the acid rest in mashing.

The protein rest is responsible for reducing the overall length of high-molecular-weight proteins – which cause foam instability and haze – to low-molecular-weight proteins in the mash. Protease enzymes comprise the group of enzymes that reduce high-molecular-weight proteins to simpler amino-acid constituents by breaking the peptide bonds between proteins. The enzymes proteinase and peptidase are two main enzymes of this group.

By far the most important change brought about in mashing is the conversion of starch molecules into fermentable sugars and unfermentable dextrins. The principal enzymes responsible for starch conversion are alpha- and beta-amylase. Alpha-amylase very rapidly reduces insoluble and soluble starch by splitting starch molecules into many shorter chains (i.e., partially-fermentable polysaccharide fractions – dextrins and maltotriose) that can be attacked by beta-amylase. Given a long enough "rest," the alpha-amylase can dismantle all the dextrins to maltose, glucose, and small, branched "limit dextrins." However, starch conversion is more effective by the faster-acting beta-amylase. Beta-amylase is more selective than alpha-amylase since it breaks off two sugars at a time from the starch chain. The disaccharide it produces is maltose, the most common sugar in malt. Together, alpha- and beta-amylase are capable of converting only 60 to 80% of the available starch to fermentable sugars.