25. The comparison of DP enzyme release and persistence with the production of yeast-fermentable sugars during a modified IoB 65°C and Congress mashes

Glen Fox (1), Evan Evans (2); (1) University of Queensland, Brisbane, Australia; (2) The Tassie Beer Dr., Lindisfarne, Australia

Technical Session 7: Brew House Operations
Monday, August 15  •  8:15–9:30 a.m.
Tower Building, Second Level, Grand Ballroom

A key biochemical process in brewing is the hydrolysis of starch by DP enzymes into yeast-fermentable sugars during the mashing stage of brewing. Efficient starch hydrolysis during mashing requires starch gelatinization at ~62-64°C, along with sufficient DP enzyme activity to achieve starch hydrolysis. This investigation considers the release of yeast-fermentable sugars in parallel with the activity of the DP enzymes during a modified IoB 65°C (1:3 grist/water + Ca), with a conventional Congress (1:4 grist/water) small-scale mash, using malt from three current Australian varieties. Traditionally, it is recognized with the DP enzymes that alpha-amylase is relatively thermostable while beta-amylase and limit dextrinase are relatively thermolabile at conventional mashing temperatures. In addition, it is know that beta-amylase, and in particular limit dextrinase, have bound and latent fractions that require release from inhibitors or binding proteins before they are able to contribute to starch hydrolysis. One empirical mechanism appears to be that the heat applied during mashing at temperatures around 55-60°C liberates these enzymes. Of similar importance is the structure of starch, which determines the temperature of gelatinization. In addition, starch branching and chain length are important to the efficiency of hydrolysis by the DP enzymes. The results in terms of starch characteristics, DP enzyme release, thermostability and activity is examined to understand the relative contribution of the DP enzymes to fermentable sugar production in the mash. Interestingly, both beta-amylase and limit dextrinase were observed to retain significant levels of activity (~40% total activity), even after mashing for 60 min at 65°C. These observations are of critical importance to brewers when they manipulate mash temperatures to cope with variations in malt quality or to develop new products. It is well understood that a mash temperature between 60 and 70°C and beyond has a substantial impact on the level and composition of wort lipids, free amino nitrogen and fermentable sugars. The level and composition of all these wort components are known to effect yeast metabolism and subsequently beer flavor. Finally, these understandings also have significant implications for 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.

Glen Fox joined the University of Queensland’s Centre for Nutrition and Food Science in October 2010, after 25 years of conducting research projects with the Queensland government. He obtained his Ph.D. degree from Southern Cross University in the area of barley genetics related to barley and malt quality. In 2008-2009, he was a postdoctoral fellow at the Department of Food Science, Stellenbosch University, South Africa, and appointed adjunct professor in 2012. In 2013, he was appointed to the College of Experts for the Global Change Institute at the University of Queensland. He has a vast amount of knowledge in value-adding of cereals, particularly barley, malt and beer quality, including starch structure and fermentability. He has collaborated with major global brewing companies and partnered in all the Australian states, the United States, Canada, South Africa, China, Ethiopia, Kenya and the United Kingdom. Glen also has research activities on maize and sorghum covering food security in several African countries. Glen is on a number of national and international technical committees, including the Institute of Brewing & Distilling Asia Pacific Section Analytical Methods Sub-committee and the European Brewery Convention Brewing Science Group.