Effects of high-gravity brewing and acid washing on brewers' yeast

Washing pitching yeast with bactericidal substances such as phosphoric acid to eliminate bacterial contamination is common practice in many breweries. Washing pitching yeast incorrectly will adversely effect the yeast and result in decreased fermentation performance. When yeast was acid washed and repitched into 12°P wort, no decrease in fermentation performance was observed but, after serially repitching in 20°P wort, a small decrease in viability was observed over the first 24 hr of the fermentation. The fermentation profile of yeast serially repitched in 20°P wort matched that of the control yeast. On examination of the wort sugar profile, a decreased rate at which glucose was removed from the wort was observed, which resulted in a lag phase before maltose could be utilized from 20°P wort. No adverse effect on glucose and maltose utilization from 12°P wort was noted. © 1998 by the American Society of Brewing Chemists, Inc.