Acid washing and serial repitching a brewing ale strain of Saccharomyces cerevisiae in high gravity wort and the role of wort oxygenation conditions

Acid washing pitching yeast is an effective method for removing bacterial c ontamination, but if the yeast is washed incorrectly decreased fermentation performance and beer quality problems may result. Various factors can affe ct the acid resistance of yeast strains during brewery fermentations. Yeast from shaking flask experiments was snore resistant to the combination of h igh gravity and acid washing conditions than yeast cropped from static ferm entations. Yeast harvested from static high gravity wort (20 degrees Plato; 1.083 OG) fermentations was move adversely affected by acid washing than y east from standard gravity (12 degrees Plate; 1.048 OG) wort. Wort oxygenat ion resulted in enhanced yeast fermentation performance and healthier yeast crops when yeast was serially repitched into 20 degrees Plate wort. Yeast cropped from fermentations with air saturated high gravity wort responded p oorly when acid washed. These results suggest that the structure of the pla sma membrane particularly the sterol and fatty acid composition, may have a n important role in tolerating high gravity wort and acid washing condition s.