Fermentation Symposium�Part II Yeast Handling Studies. I. Agitation of Stored Pitching Yeast.

McCaig, R. and Bendiak, D.S.

Abstract
The effects of agitation on stored production yeast were studied to improve yeast handling procedures. Yeast stored 5 days at 1�C with constant agitation decreased in viability by 25% and in glycogen, 85%. The yeast cells were granular, and slurry cell numbers were reduced by 15% owing to mechanical breakage caused by the agitation. Yeast stored with no agitation (still) under beer or water decreased in viability only 8% and in glycogen content, 12%. Yeast stored with a 2-hr agitation per day (a time long enough to maintain slurry homogeneity) did not differ significantly from yeast stored still. When the stored yeasts were pitched into high gravity worts (15.1� P), yeast stored still and yeast stored with minimal agitation produced similar results in terms of attenuation rate, final attenuation, yeast in suspension, pH, alcohol production, final diacetyl concentration, and dimethyl sulfide concentration. Significant differences were noted in fermentations pitched with yeast constantly stirred during storage. Attenuation was slower, final attenuation was higher, yeast in suspension was lower and slower to increase in numbers, and the concentrations of diacetyl and dimethyl sulfide were much higher than the aforementioned types.
Keywords: Agitation, Attenuation, Beer quality, Yeast viability