Program Book - Master Brewers Association of the Americas

Poster Session: Yeast
Moderator: Grady Hull, New Belgium Brewing Company, Fort
Collins, CO
Grady Hull graduated from Colorado State University in 1994 with
a B.S. degree in food science and technology. After an internship with
Coors Brewing Company, he worked as a brewer for CooperSmith’s
and Fleetside brewpubs. In 1996 he began working at New Belgium
Brewing Company where he is currently the assistant brewmaster.
While working at New Belgium he received his M.S. degree in
brewing and distilling from Heriot-Watt University.
P-209
Withdrawn
P-210
Serial repitching of dried lager yeast
TOBIAS FISCHBORN (1), Chris Powell (1), Michel Gauthier (2),
(1) Lallemand Inc., Montreal, QC, Canada; (2) Maska Laboratories,
St. Hyacinthe, QC, Canada
Although there is a diverse range of applications for active dried
yeast (ADY) within the brewing industry, one of its major functions
is as a replacement for freshly propagated yeast slurry. Recent
reports have suggested that employing brewers ADY may lead
to fermentation inconsistencies such as poor flavor production
and aberrant flocculation. However, analysis of the fermentation
performance of ADY typically involves a comparison between dried
yeast and a brewing yeast culture which has already been used for
several serial repitchings, rather than a freshly propagated slurry.
It is widely accepted that freshly propagated yeast is not perfect
in terms of its fermentation performance and that the subsequent
beer is often blended to eliminate any negative characteristics.
Consequently, comparing the fermentation characteristics of beer
produced with serially repitched yeast and ADY may be misleading.
Here we evaluate the fermentation performance of wet and dried
lager yeast over the course of serial repitching to investigate the
differences between fresh and repitched cultures for each type
of yeast. In addition, the capacity of yeast populations to adopt
fermentation characteristics typical of the strain during serial
repitching was determined. Each fermentation was monitored for a
variety of characteristics, including sugar utilization and production
of flavor compounds, higher alcohols and esters. In addition,
yeast cultures were monitored for viability and the presence of
petite mutants, flocculent variants and changes to the genome
structure. The latter was assessed by analyzing chromosome length
polymorphisms and the stability of delta regions flanking yeast
transposons. The data presented here indicate that brewers’ ADY
can be used for serial repitching without any long term adverse
affects in terms of genetic stability or fermentation performance.
Tobias Fischborn was appointed as research scientist for Lallemand
Inc. in March 1998. He is now responsible for brewing research and
development at Lallemand and is also responsible for quality control
and quality assurance of all brewing yeasts. He graduated from
the Technical University Munich/Weihenstephan in 1993, where he
obtained an engineering degree in brewing and beverage technology.
He continued studying for a Ph.D. degree in brewing, which he
finished in 1997. Prior to his studies in Weihenstephan, he worked as
a brewer at Brewery Ph. & C. -Andres in Kirn, Germany.
168
P-211
Differential transcription of genes involved in nutrient uptake
during full-scale brewery fermentation
BRIAN GIBSON (1), Chris Boulton (1), Wendy Box (1), Neil Graham
(1), Stephen Lawrence (1), Robert Linforth (1), Katherine Smart (1)
(1) University of Nottingham, United Kingdom
Changes in the nutrient composition of wort during brewery
fermentation can directly affect yeast metabolism and growth and
influence the flavor profile of the final product. The complexity
of wort compositional change is matched by the complexity of the
yeast cell’s response to these changes. In this study, changes in the
lager yeast transcriptome during full-scale (3275 hL) lager wort
fermentation were measured with the aid of oligonucleotide-based
DNA arrays and were compared to changes in the fermentable
carbohydrate and amino acid composition of the wort. Of the 32
genes involved in transmembrane transport of amino acids, all
showed statistically significant changes in expression, with maximal
transcription typically coinciding with amino acid limitation.
Genes encoding the low affinity amino acid permeases displayed
differential transcription profiles, suggesting a synchronized
functionality, with at least one transporter operational at any given
time. Genes involved in sugar transport similarly demonstrated a
significant differential change in transcription. The HXT and MAL/
MPH genes, which encode proteins involved in the transmembrane
transport of sugars, displayed transcriptional profiles consistent
with their susceptibility to carbon catabolite repression and the gene
products’ biochemical affinities for sugars. A notable exception was
the HXT4 gene, which had relatively high transcriptional activity
under high sugar conditions, despite being a high affinity glucose
transporter. The transcriptional changes observed are discussed
in relation to their significance to brewery fermentation, yeast
metabolism and flavor development.
Brian Gibson was awarded a first-class honors degree in science at
University College Dublin in 1999, where he stayed to complete a
Ph.D. degree in the School of Biology and Environmental Science.
His Ph.D. research focused on the beneficial effects of plant/fungal
symbioses in heavy-metal polluted soils. In 2004 Brian joined
Katherine Smart’s research group at Oxford Brookes University as a
post-doctoral researcher, where his work focused on the antioxidant
responses of brewing yeast to oxidative stress. Brian is currently a
post-doctoral research fellow at the University of Nottingham. His
current research interests include stress responses of yeast during
industrial brewery handling, the genome-wide changes that occur in
yeast during brewery propagation and fermentation, and the factors
influencing the integrity of brewing yeast mitochondrial DNA. Brian
is a member of the British Mycological Society, the Society for Applied
Microbiology, and the Society for General Microbiology.