The Impact of Sedimentation on Cone Yeast Heterogeneity

摘要

Studies of yeast obtained postfermentation have largely considered individual cells within the crop to be phenotypically and genotypically similar. However, previous studies have indicated that environmental conditions within the cone of a cylindroconical vessel are variable, suggesting that physiological and potentially genetic heterogeneity may occur. Two 2,000-hL fermentation vessels, pitched in parallel with a lager strain, were cropped using two regimens and yeast fractions obtained at 500-kg intervals. Each yeast fraction was analyzed for factors impacting fermentation performance. In addition, characteristics of the barm beer were investigated. Analysis of yeast postfermentation indicated extensive heterogeneity within the crop, in terms of physiological condition, floc-culation potential, cell size, and replicative age. In addition, environmental conditions within the cone were also observed to vary substantially. Gradients in terms of temperature, pH, gravity, and ethanol were all detected within the cone. Although cropping regimens can differ, it is proposed that variation in yeast quality throughout the cone may facilitate selection during cropping. Successively cropping and pitching with a specific portion of the cone may lead to the accumulation of a population comprising cells with inappropriate fermentative characteristics, potentially leading to fermentation inconsistency.