Powell, C. D.1 and Brindley, S.1, (1)University of Nottingham, Loughborough, UNITED KINGDOM
Technical Session 4: Yeast
Monday, June 05, 2017
3:30–4:45 p.m.
Camellia AB
Brewery fermentations are unique in that it is common practice to harvest (crop) the yeast at the end of fermentation and re-inoculate (repitch) the culture into 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 repitchings (generations). It is well known that some yeast strains can be reused many times with little apparent effect on product quality. However, other strains are less tolerant of repitching, and these populations can display genetic and/or phenotypic drift over time, ultimately influencing the capacity of the population to produce beer within product specifications. Although brewing yeast cultures are typically considered to comprise cells that are all identical in nature, it is known that microbial populations often exhibit differences between individuals. At the basic level, this may result in a decreased fitness to ferment, resulting in inconsistent fermentations, extended vessel residence times and potentially necessitating changes to downstream processing, leading to increases in overall manufacturing costs. In this study we investigate aspects of population variability to determine the underlying causes behind changes to brewing yeast populations. This includes the potential for selection during repitching, the genetic stability of production strains, and the analysis of population heterogeneity in ale and lager production strains. Yeast populations were characterized using a variety of DNA fingerprinting methods, and heterogeneity was assessed through analysis of resistance to key stress factors, as determined via a series of physiological assays based on growth behavior. During this presentation, we show data indicating the degree of heterogeneity within brewing yeast populations, specifically related to physiological attributes, stress tolerance and key performance indicators. We also explore the relationship between fermentation conditions and population heterogeneity, and the potential for the selection of cells based on this. Finally, we provide details on whether population heterogeneity is indeed a negative attribute and how this information can be used to understand quality and fermentation consistency. It is anticipated that this research will enable us to develop a deeper understanding of the scientific basis of yeast population variation under stressful but non-lethal conditions. This project is directly relevant to the brewing industry, as well as others who employ fermentation and/or cultivation of yeast on a large scale and impinges on a number of sectors worldwide, including baking, oenology, distilling, and animal/human nutrition.
Chris Powell holds a Ph.D. degree on yeast cellular aging and fermentation performance from Oxford Brookes University, U.K. (2001). After a post-doctoral research position at the same institute investigating rapid methods for detection of contaminants in beer (2001–2004) he worked in the Research Department for Lallemand Inc., Montreal, Canada (2004–1010), ultimately occupying the positions of senior scientist in brewing research and project manager in genetic identification. In 2010 Chris moved to the University of Nottingham, where he is currently an assistant professor in yeast and fermentation. His core subject areas include yeast physiology and fermentation biotechnology, particularly related to the brewing, beverage and sustainable bioenergy sectors. Chris is the author or co-author of more than 50 publications, a member of the ASBC Journal editorial board and a regular reviewer for many other scientific journals. He has previously served as chair of the ASBC Technical Committee and has held a position on the ASBC Board.
