Download Stress Tolerance in Group 1 and 2 Lager Brewing Strains

STRESS TOLERANCE IN GROUP 1 AND 2 LAGER
BREWING STRAINS
Pauline Chabert, Tobias Fischborn and Chris Powell
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 species. Recently 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, osmotic and oxidative stress.
The data obtained and presented here indicates 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. Furthermore, this
analysis is significant for the active dried yeast industry, where robust brewing yeast strains are
required to withstand stress factors associated with desiccation, in addition to favourable
properties during fermentation.
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