GROWTH AND FERMENTATION CHARACTERISTICS OF BOTTOM BREWER YEAST UNDER MECHANICAL STIRRING

Fermentation kinetics of bottom brewer's yeast under mechanical stirring was investigated by varying the agitation speed, fermentation temperature, and inoculum size. Mechanical stirring reduced the fermentation time from 9 to 6 d compared with non-mechanical agitation. However, formation of esters such as ethyl- and isoamylacetate seemed to be suppressed. Although the fermentation was drastically accelerated by an increase in the temperature, flavor components such as isoamylalcohol and ethylacetate were considerably changed compared with those of conventional lager-type beer. By a combination of mechanical stirring and increase of inoculum size, the fermentation time could be reduced to 4 d, even at the low temperature of 8-degrees-C. Further intensive work is needed to overcome the comparatively low formation of esters, which play an important role in the flavor of beer.