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A key biochemical process in brewing is the hydrolysis of starch by diastatic power (DP) enzymes into fermentable sugars during the mashing stage of brewing. Efficient starch hydrolysis during mashing requires initially starch gelatinization at approximately 59–64°C and then sufficient DP enzyme activity to achieve starch hydrolysis. This investigation compared the persistence of DP enzyme activity during modified Institute of Brewing (MIoB, 1:3 grist/water ratio + Ca2+) mash with the conventional Congress (1:4 grist/water ratio) small-scale mash, using malt from three current Australian barley varieties. Traditionally, with the thermostability of DP enzymes, it is understood that α-amylase is relatively thermostable, whereas β-amylase and limit dextrinase (LD) are relatively thermolabile at conventional mashing temperatures. In addition, it is also known that β-amylase and in particular LD have bound and latent fractions that require release from binding proteins or inhibitors, respectively, before they are able to contribute to starch hydrolysis. One mechanism observed empirically was that heat applied during mashing at temperatures of approximately 55–60°C appears to liberate bound β-amylase and LD. The results in terms of DP enzyme release, thermostability, and activity were examined to understand the relative contributions of the three key DP enzymes to starch hydrolysis during different mashing conditions. Interestingly, we observed that both β-amylase and LD retained significant levels of activity (approximately 40% total activity), even after mashing for 60 min at 65°C. These observations are of critical importance to brewers in meeting beer quality specifications when they manipulate mash temperatures to cope with variations in malt quality, developing new products, or producing beers requiring different wort qualities for production. The implications from these results of the choice of small-scale mash protocol for malt quality evaluation, the targeting of DP enzyme alleles for barley malt quality improvement, and the selection of malt for brewing are discussed. Keywords: Malt, Diastatic power enzymes, Mashing, Thermostability
