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.
