Technical Session 14: Yeast II Session
Tinne Dekoninck, Catholic University of Leuven, Heverlee, Belgium
Co-author(s): Filip Delvaux and Freddy Delvaux, Catholic University of Leuven, Heverlee, Belgium
ABSTRACT: Beer refermentation, i.e., bottle conditioning,
is a frequently used technique among breweries in Belgium, the United
Kingdom, and the United States. To achieve a secondary fermentation in
the bottle, mature beer is inoculated with yeast and fermentable
extract, whereupon it is refermented in preferably less than two weeks.
Bottle conditioning results in fully saturated beer with an enriched
flavor perception and prolonged flavor stability. Since export and
consumption of bottle conditioned beers still increases, it is of major
economic importance that constant product quality can be assured.
Although beer refermentation seems uncomplicated, the process faces
important pitfalls presumably because of yeast stress. Indeed, beer is
far from an excellent fermentation medium since it differs from an ideal
wort medium in its alcohol and carbon dioxide content and low nutrient
availability. To improve the process of bottle conditioning, several
perspectives can be considered. In a first experiment, the
refermentability of several Belgian beers (both lager and ale types) was
investigated to reveal the impact of beer related parameters on
refermentation. A striking finding was a strong influence of initial
beer alcohol levels on refermentation performance, especially when a
less ethanol tolerant yeast strain was used. To improve the
refermentation performance of different yeast strains, a promising
strategy could, therefore, be the adaptation of yeast to alcohol, prior
to beer inoculation. In a second experiment, yeast was propagated both
in a dynamic and static way, with variable extract and alcohol levels.
Throughout propagation and refermentation, important yeast physiological
parameters were monitored, such as viability, glycogen and trehalose
content, fatty acid and ergosterol levels, as well as the expression of
(stress related) genes. These analyses revealed physiological
differences between statically and dynamically propagated yeast, as well
as between alcohol conditioned and reference yeast populations. Our
findings indicate that the use of appropriate conditioning of yeast
provides promising opportunities to increase yeast refermentation
performance during bottle conditioning of beer.
Tinne Dekoninck
graduated in 2008 as a bio-engineer in chemistry (food technology) from
the Catholic University of Leuven. For her M.S. thesis, she joined the
Centre for Malting and Brewing Science to study the feasibility of high
cell-density brewery fermentations. After graduation, she obtained a
grant from the Institute for the Promotion of Innovation Through Science
and Technology in Flanders (IWT) and started a Ph.D. program at the
Centre for Malting and Brewing Science, under the supervision of Freddy
Delvaux. Her research focuses on the impact of yeast physiology on
bottle conditioning of beer.
VIEW PRESENTATION 48
