26. Yeast stress when fermenting at high gravity—Sources, damage and the cellular response

Chris Powell (1); (1) University of Nottingham, Nottingham, U.K.

Technical Session 8: Yeast Stress & Performance
Monday, August 15  •  8:15–9:30 a.m.
Tower Building, Majestic Level, Majestic Ballroom

Very high-gravity (VHG) fermentations >20°P are increasingly employed within the brewing industry to maximize process efficiency. However, it is known that the use of VHG worts can create issues during fermentation, particularly with regard to achieving the desired final product specifications. From the perspective of the yeast culture, the environment of VHG wort is considerably different from that of standard worts, and this can impact the health and function of the population. The resulting detrimental effects can include longer fermentation times, altered flavor characteristics and, in some instances, incomplete or inefficient conversion of sugars to ethanol. Many of these artifacts are related to yeast health and it is accepted that VHG conditions place increased stress on yeast. However, little is known regarding the precise character and intensity of these stress factors and their direct effects on individual cells. Here we characterize the wort environment with regard to potential for oxidative and osmotic stresses and describe the impact of these factors on yeast physiology, DNA integrity and organelle damage. In addition, the relationship between initial wort gravity, fermentation progression and the promotion of intracellular anti-stress mechanisms involved in cell homeostasis and repair will be discussed. It is anticipated that the data generated and presented here will provide insight into some of the challenges faced by yeast in fermenting worts of particularly high sugar concentration, as well as potential mechanisms for alleviating stress.

Chris Powell holds a Ph.D. degree on yeast cellular aging and fermentation performance from Oxford Brookes University, UK (2001). After a postdoctoral 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 and project manager in genetic identification. In 2010 Chris moved to the University of Nottingham, where he is currently a lecturer 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 40 publications and a regular reviewer for several scientific journals. He has previously served as chair of the ASBC Technical Committee and has held a position on the ASBC Board of Directors since 2010, currently acting as vice president.

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