Stress tolerance in group 1 and 2 lager brewing strains

Yeast and Fermentation Session
Chris D Powell, The University of Nottingham, UK
Co-author(s): Tobias Fischborn, Lallemand Inc., Canada

ABSTRACT: Saccharomyces pastorianus strains are natural hybrids of S. cerevisiae and S. bayanus yeast and display properties particularly suited to the production of lager type beers. While it is accepted that lager strains arose approximately 200 years ago following a mating reaction between these two species, recent evidence has suggested that such an event may have occurred more than once in the evolution of this yeast. It has been suggested that the S. pastorianus species may contain two subgroups, designated Saaz (Group 1) and Frohberg (Group 2), as a result of separate mating events. These groups have been broadly differentiated according to a number of criteria including genome rearrangements, gene copy number, DNA sequence polymorphisms, and differences in ploidy. Despite detailed genetic analysis, only limited studies have previously been performed to characterize their phenotypic properties. The purpose of this study was to investigate the similarities and differences between the physiological characteristics of Saaz (Group 1) and Frohberg (Group 2) yeast. A number of strains belonging to each group were selected and assessed for their growth characteristics and their capacity to assimilate sugars. Furthermore, each strain was analyzed for its ability to withstand stress factors associated with the production of alcoholic beverages, including temperature and osmotic and oxidative stress. The data obtained and presented here indicate that there are some fundamental differences between the capacity of each yeast group to respond to their immediate environment. While this is particularly interesting for the understanding of lager brewing yeast strain variation, it may also be significant for associated industries such as the biofuel industry, where investigation into the properties of industrial yeast strains is of particular importance, or the active dried yeast industry, where robust brewing yeast strains are required to withstand stress factors associated with desiccation, in addition to favorable properties during fermentation.

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.