The Relationship Between Yeast Cell Age, Fermenter Cone Environment, and Petite Mutant Formation in Lager Fermentations

摘要

Fermentation performance and final beer product quality can be greatly influenced by the integrity of brewing yeast mtDNA, particularly when petite mutants are formed. The factors that influence the susceptibility of cropped yeast to form petites are not fully understood. Analysis of the yeast crop harvested from an industrial scale fermentation vessel showed that the greatest accumulation of petite mutants was colocated with the oldest (in terms of replicative age) yeast cells. The frequency of petites is also known to be dependent on the generation age (number of successive fermentations completed) of the crop. Using ethidium bromide, the susceptibility of populations enriched with virgin and non-virgin yeast cells to petite formation was investigated. It was observed that newly formed daughter (virgin) cells are more resistant to artificially induced petite formation. This resistance was not influenced by mtDNA copy number, since virgin cells were observed to exhibit a lower mtDNA copy number than mother (non-virgin) cell populations. The results from this study suggest that accumulated damage to DNA is of greater influence than the mtDNA copy number in the formation of spontaneous petites.