Impact of the Long-Term Maintenance Method of Brewer's Yeast on Fermentation Course, Yeast Vitality and Beer Characteristics

Abstract

J. Inst. Brew. 117(3), 383–388, 2011 The effect of the long-term maintenance method used with a brewer’s yeast on its technological properties was determined in laboratory fermentation trials with a 12°P all-malt wort. The trials were performed at a constant temperature and under conditions of constant substrate concentration. Two cultures of a bottom fermenting yeast, Saccharomyces pastorianus RIBM 95, were tested – one culture was maintained by subculturing on wort agar slopes at 4°C and the other culture underwent a three year storage in liquid nitrogen at minus 196°C. Parameters under investigation included yeast vitality measured as acidification power (AP), fermentation time needed to reach an alcohol level of 4%, the yeast cell count, sedimentation of the yeast during the fermentation, and the production of beer flavour compounds in green beer. The yeast culture stored for three years in liquid nitrogen displayed a higher count of suspended cells, required a shorter time to attenuate the wort to produce 4% alcohol and produced a 1.5 to 2.5-fold higher concentration of a number of flavour compounds. The long-term storage method did not affect the sedimentation ability and vitality of the yeast strain tested.