High mashing thickness negatively influences gelatinisation of small and large starch granules and starch conversion efficiency during barley malt brewing

Abstract

The breakdown of starch into fermentable sugars is essential for several industrial processes, including beer production. Nowadays, high ratios of barley malt to water are used to improve brewhouse efficiency. Recent findings, however, indicate that small starch granules in barley malt could reduce starch conversion efficiency. In this study, the gelatinisation behaviour of small and large starch granules in function of mashing thickness was assessed. A mashing process was performed with malt to water ratios ranging from 1:6 to 1:2.5 (high gravity), leading to wort with 12 and 25 g of extractable components per 100 g wort, respectively. The sugar yield in wort decreased from 79% to 66% with increasing malt to water ratios due to reduced maltose production. It was hypothesised that sugars and other components in the mash increased the starch gelatinisation temperature. Therefore, small and large starch granules were isolated from barley malt, and the impact of wort and individual wort component on the gelatinisation temperature of these granules was assessed. An increase in the amount of extracted components with 2.5 g per 100 g wort during mashing resulted in a 1 °C increase in starch gelatinisation temperature for both types of granules. For high gravity brewing, this proved problematic. Gelatinisation was delayed to such an extent that β-amylase was not able to produce the maximal amount of fermentable sugars from primarily the small starch granules anymore, explaining the reduced sugar yield. • Mashing yield and sugar yield decrease with increasing mashing thickness. • The loss in sugar yield is due to less efficient maltose production. • Starch losses during mashing can be mainly attributed to small starch granules. • The impact of wort on starch gelatinisation is similar for large and small granules. • Extract content of wort is strongly correlated with starch gelatinisation temperature.