High Gravity Brewing Utilizing α-glucosidase (Part 4)

Application of Parallel Fermentation Utilizing α-glucosidase

Abstract

High gravity brewing has come to be widely used for increased brewery efficiency. However, it is not easy to maintain good yeast performance during fermentation because of the stress on yeastcaused by high sugar and/or ethanol concentrations. Therefore, sugar attenuation tends to be insufficientand the finished beer contains high concentrations of acetic acid and esters.
We previously reported on the development of a new fermentation method by which severaldifficulties in high gravity brewing could be overcome. In this method, α-glucosidase added at thebeginning of fermentation enables the conversion of wort sugars by glycosyl-transfer and hydrolyticreactions to proceed in parallel with ethanol formation by yeast. By using α-glucosidase, we succeededin high gravity brewing with a top fermentation brewer's yeast at a constant fermentation temperatureof 15°. However, bottom fermenting brewer's yeast is more widely used for commercial brewing aroundthe world. In this paper we report results of using the method with bottom fermenting brewer's yeast. We confirmed that the method could be successfully applied to high gravity wort fermentation withbottom fermenting yeast at low temperature. When α-glucosidase was added to 20% Plato wort at aconcentration of 800mg/l, the wort was successfully fermented at 10° with a bottom fermenting brewer's yeast, W 34/70. The real degree of fermentation was 77%, which was 16% higher than that ofthe control fermentation, and the concentration of acetic acid was 200mg/l, which was 85mg/l lowerthan that of the control. The addition of α-glucosidase was also effective for increasing the degree offermentation of dextrinous wort. When α-glucosidase was added at the concentration of 400mg/l to 20% Plato wort containing 6.2% dextrin, the content of dextrin decreased to 3.7% by the end of fermentationwith a top fermenting brewer's yeast, NCYC 1245; the real degree of fermentation was 75%, whichwas 19% higher than that of the control. It is suggested that the use of α-glucosidase is applicable forbrewing good beers from wort that have a low proportion of fermentable sugars, meaning that malt withlower diastatic power could be utilized. The use of enzymes in fermentation would open several newpossibilities to add to existing enzyme methods, such as the use of acetolactate decarboxylase to shortenthe conditioning period or glucoamylase for dry beer brewing.