Fermentation Symposium�Part II Yeast Handling Studies. II. Temperature of Storage of Pitching Yeast.

McCaig, R. and Bendiak, D.S.

Abstract
The methods employed in handling production yeast before pitching are important. Fermentations pitched with improperly handled yeast could experience problems such as hanging fermentations or poor attenuation or both. The temperature of yeast storage is a major factor when considering handling procedures. Yeast stored 6 days at 1�C showed a 5% drop in glycogen content and a 7% drop in viability. The same yeast stored at 5�C decreased 22% in glycogen content and 14% in viability. At storage temperatures of 10, 15, 20, and 25�C, significant reductions in glycogen content (up to 79%) and viability (up to 68%) occurred. Fermentations pitched with yeast stored at 1 and 5�C showed little difference in numbers of yeast in suspension; rate or attenuation; final attenuation; diacetyl, alcohol, and dimethyl sulfide concentrations; or final pH. Fermentations pitched with yeast stored at 10�C exhibited higher final diacetyl and dimethyl sulfide concentrations. The fermentations pitched with yeast stored at 15, 20, and 25�C did not ferment normally; rate and extent or attenuation were poor; the number of yeast in suspension was abnormal; subsequent yeast crops were less; diacetyl, alcohol, and dimethyl sulfide concentrations were less; and final pH was much higher.
Keywords: Attenuation, Beer quality, Temperature, Yeast viability