Technical Session 03: Yeast I Session
Urs Wellhoener, Boston Beer Company, Boston, MA, USA
Co-author(s): Annette Fritsch, Boston Beer Company, Boston, MA, USA
ABSTRACT: There are a variety of factors that indicate
maturity based on the beer system, and the identification of a mature
sample is based on the beer itself, particularly fermentation
by-products, dry hopping, and spicing. Commonly, the main focus is from
the analytical perspective. This includes parameters like diacetyl or
acetaldehyde. However, what other factors designate the right maturation
time, primarily after active fermentation is complete and the beer is
in basically “static” storage? In this study, a spiced, lager beer was
evaluated during storage using both chemical analysis for a wide range
of fermentation by-products and sensory descriptive analysis. Similar to
dry-hopping, the aroma and flavor impact of spices unfold depending on
interactions with other compounds in the beer. The synergies and
inhibitions among compounds change during maturation. Therefore, it was
essential to evaluate how the impact of spices changes during storage.
Analysis techniques including ANOVA and PCA were applied to both the
chemical and sensory data to determine the optimal maturation time. In
addition to identifying optimal maturation, the level of yeast carry
over into static storage was explored. A moderate yeast carry-over is
desired to help the beer to mature further (e.g., diacetyl) but should
be kept minimal to minimize yeast autolysis, which can affect beer
aroma/flavor and foam negatively. Since the beer in this study was
“completely end-fermented,” prior to hitting the storage tanks, the
question of whether yeast should be removed completely via
centrifugation at fassing was addressed as well. Through a combination
of analytical techniques, we were able to identify both the impact of
storage on a spiced lager beer and the effect of varying levels of yeast
carry-over on the storage profile. A panel of sensory experts rated the
maturity of the beer according to attributes like overall maturity,
spice, diacetyl, acetaldehyde, etc.
Urs Wellhoener, the
corporate manager for yeast and fermentation for the Boston Beer
Company, joined the company in October 2007. His focuses are yeast
management and microbiology. He is a technical graduate as a brewer and
maltster (1991–1993) and received a Dipl.-Eng. degree from the Faculty
of Brewing and Food Technology of the Technische Universität
München-Weihenstephan (TUM) in 1999. After graduation in 1999 he was a
project manager on a yeast project at Veltins Brewery,
Meschede-Grevenstein (1999–2000). Between 2000 and 2007 Urs was a
scientific assistant and doctorate at the Chair of Brewing Technology II
at the Weihenstephan Center of Food and Life Sciences, Technische
Universität München-Weihenstephan (TUM). He received his Ph.D. degree
for his studies on yeast physiology during fermentation and propagation.
During this time he also worked for Muellerbraeu, Pfaffenhofen/GER, as
QC manager.
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