Fermentation Symposium—Part II Yeast Handling Studies. I. Agitation of Stored Pitching Yeast.
McCaig, R. and Bendiak, D.S.
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