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Mashing
Chemical Changes at Mashing
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).
Acid Rest
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.
Protein Rest
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.
Starch Conversion
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 (9).
Factors Affecting Mashing Conditions
Temperature: Temperature influences the amount of extract produced (yield) and the fermentability of the wort during mashing. In general, the higher the temperature, the greater the yield but the lower the fermentability of the wort. At lower temperatures less extract is produced, but fermentability is higher. Only at very high temperatures will extract begin to drop off.
Mash Times: Mash times are another factor influencing yield and the fermentability of the wort. In general, longer mash times increase the concentration of the extract, but the rate of increase becomes slower and slower (17). In general, short mash times at high mash temperatures will produce more dextrinous worts, while longer mash times at high temperatures produce more fermentable worts.
Mash pH: The optimum pH range for mashing is generally at 5.5 to 5.6 for both amylases (17). The "normal" mash pH, however, depends on the type of malts employed, the pH of the water, and the method of mashing. The mash cycle should not be started until the proper initial mash acidity is approximated (within pH 0.2).
Malt Modification: The temperature used for mashing is a function of malt modification. This is because the extent of modification influences the rate of starch solution. Lower temperatures are needed for well-modified malts because most of the enzymes are destroyed in the kiln, particularly beta-amylase, which is necessary for starch conversion.
Water Ions: The nature of the mashing water has an important influence on mash reactions. The ions of major importance at mashing are those of calcium and carbonate, with magnesium and sodium ions playing lesser roles (6). Calcium lowers the pH of the mash mainly by its interaction with phosphates and to a lesser degree with protein from the malt. Carbonate ions operate in the reverse direction.
Quantity of Water: The total quantity of water required for mashing varies between 2 and 5.5 hl/100 kg of malt, depending upon the mashing method adopted and the required gravity of the wort. The total quantity of water is usually lower for infusion mashing (2 to 3 hl/100 kg of malt) and higher for decoction mashing (3 to 5.5 hl/100 kg of malt).
Mash Thickness: Thin mashes favor the conversion of starch to sugars, while in thick mashes the rate of saccharification is retarded, probably because the accumulating sugars competitively inhibit the hydrolytic enzymes (9). Therefore, thick mashes produce more glucose and maltotriose, which contain dextrins, while dilute mashes favor the production of sucrose and maltose, and thus wort attenuation.
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