Factors influencing proteinase A activity during the production of unpasteurised beer

Compared with pasteurised beer, a decline in foam retention during storage is an issue for unpasteurised beer. The major reason for this is that proteinase A is able to slowly breakdown foam promoting proteins in beer. Therefore, controlling the activity of proteinase A is key to solving this problem. In this study, foam quality in unpasteurised beer was studied systematically on a commercial scale considering factors including yeast activity, strain, generation number and storage time. Accordingly, yeast handling procedures to manage proteinase A activity were established: (1) yeast strain P with reduced proteinase A should be used in production; (2) storage time of recovered yeast should be no more than two days; (3) proteinase A activity in recycled yeast slurry should be less than 10x10(-5) U/mL and (4) the number of yeast generations should be less than three. With the application of these measures, proteinase A activity was significantly decreased, and the corresponding foam quality was improved. (c) 2020 The Institute of Brewing & Distilling