The impact of the thermostability of α-amylase, β-amylase and limit dextrinase on potential wort fermentability

Diastatic power (DP), a measure of the level of activity of starch-hydrolyzing enzymes, is a term that refers to the combined activity levels of β-amylase, α-amylase, limit dextrinase, and α-glucosidase. The result of the action of these enzymes during brewing is to break down starch into component sugars that are readily fermented into alcohol by yeast. Although DP is a reasonable predictor of fermentability, it does not always accurately estimate the level of fermentable sugars generated during mashing or the subsequent fermentability of the resultant wort. Previously, it has been shown that allelic variation in β-amylase thermostability has a significant impact on wort fermentability. The thermostability of the DP enzymes is critical in determining fermentable sugar yield during mashing, where the mash temperature profile is a balance between the temperature required for starch gelatinization to enable efficient hydrolysis and the rate of thermal inactivation of the DP enzymes. This study demonstrates that there is significant variation in the thermostability of α-amylase and limit dextrinase in malts made from a wide range of Australian and international malting barley varieties. This variation in α-amylase and limit dextrinase thermostability combined with that of β-amylase provides an opportunity for barley breeders to produce divergent malting varieties that better fulfill brewers' fermentability requirements. The implications of the varying DP enzyme thermostability on the selection of malt by brewers to optimally suit different brewing styles and regimens are outlined.