Changes in Brewer's Yeast during Storage and the Effect of These Changes on Subsequent Fermentation Performance

A slurry of brewer's yeast in beer was stored in two, 200-bbl cylindroconical vessels at 1.6° C. One was maintained full, while 34% of the yeast was removed from the other vessel after 24 hr. The yeast was stored in both vessels for a total of 80 hr. Samples were removed at intervals and analyzed for glycogen, trehalose, and viability. Aliquots of each yeast sample were pitched into 2 L of wort. Yeast glycogen and trehalose declined only slightly in the full vessel, but in the other vessel, glycogen declined significantly after removal of a portion of the yeast. Viability of the yeast stored by either method remained between 90 and 96%. Fermentations of the yeast stored by either method showed no relationship between yeast fermentation performance and glycogen or trehalose content. The fermentation performance of yeast stored under these industrial conditions was independent of glycogen or trehalose content and several reasons for this are discussed.