Modelling the Contribution ofAlpha-Amylase,Beta-Amylase and Limit Dextrinase to Starch Degradation During Mashing

Response surface methodology was used to determine the levels ofalpha-amylase,beta-amylase and limit dextrinase enzymes required for efficient conversion of starch to fermentable sugars during mashing. Micro-scale mashes with purified barley starch and malt enzymes were performed in a Brewing Research Foundation mash bath, and mash liquors were analysed for solubilised starch, reducing sugars (neocuproine assay) and fementable sugars (anion exchange HPLC). Fermentable sugars in the mash liquor were positively correlated with reducing sugars (R²=0·94) and the percentage of starch solubilised during mashing (R²=0·68). A multiple regression equation relating the levels of the three starch degrading enzymes to the percentage of starch hydrolysed to fermentable sugars gave a good fit to the second order response surface (R²=1·00, RMSE=1·37%). Addition of limit dextrinase to the mashes resulted in a substantial increase in levels of fermentable sugars, and limit dextrinase showed a synergistic effect in increasing levels of maltose in the mash liquor when combined with high levels ofbeta-amylase. The efficiency of any one starch degrading enzyme in a mash is influenced by the presence of other starch degrading enzymes. Commercial malts contain excess levels ofbeta-amylase and below optimal levels of limit dextrinase. Malt extract may not be a good indicator of the level of fermentable carbohydrates produced during mashing.