Genetic drift and variation in brewing yeast cultures

Technical Session 22: Yeast IV Session
Chris D Powell, The University of Nottingham, UK
Co-author(s): Thien-Khiem Nguyen, University of Nottingham, UK

ABSTRACT: Once a brewery fermentation has reached completion, it is common practice to harvest the yeast from the fermentation vessel and use the recovered biomass to inoculate a fresh batch of wort in a process known as serial repitching. Repitching yeast often results in a reduction in yeast quality over time, although the extent to which this occurs depends on the individual yeast strain and the number of serial repitchings (generations). It is well known that some yeast strains are able to be reused many times with little apparent effect on product quality. However, other strains are less tolerant to repitching, and these populations can accumulate mutant cells that ultimately influence the capacity of the population to produce acceptable beer. While process and product parameters may play a significant role in the number of times a strain can be reused, it is also possible that some industrial strains are simply more genetically malleable than others. Previous studies have shown that chromosomal rearrangements manifest themselves in laboratory S. cerevisiae yeast after 30–50 generations under nutrient limited conditions. However, the rate of mutation in polyploid industrial brewing strains under sub-lethal but stressful conditions has not been investigated. Here the relationship between brewery process conditions, associated stress factors, and genome stability is investigated. Furthermore, we explore the potential for selection during full scale beer production and the significance of this on population dynamics. It is anticipated that the data will provide a greater understanding with regard to the number of times which a yeast culture can be expected to perform to its optimum capacity.

Chris Powell holds a Ph.D. degree on the subject of yeast cellular aging and fermentation performance from Oxford Brookes University, U.K. Chris has also occupied research positions at Bass Brewers (now Coors UK) and more recently at Lallemand, based in Montreal, Canada. During his six years at Lallemand, Chris was responsible for the R&D laboratory for the molecular identification and characterization of micro-organisms utilized within the food and beverage industries, in addition to research focused on brewing yeast. In 2010 Chris returned to the United Kingdom to take up his current position as lecturer in yeast and fermentation at the University of Nottingham. Chris is presently involved in research in the areas of both brewing science and sustainable bioenergy. Chris is the author or co-author of more than 40 scientific publications and is a regular reviewer for several scientific journals. Chris has also served on the ASBC Technical Committee since 2005 and the ASBC Board of Directors since 2010. Outside of work, Chris is a keen soccer player and spends a significant portion of his time running, hiking, and exploring different parts of the world.