Technical Session 01: Hops I Session
Hitoshi Takemura, Kirin Brewery Company, Limited
ABSTRACT: Hop aroma is a very important factor that
contributes to the flavor of beer; therefore, a great deal of care is
taken to adjust hop aroma by controlling brewing parameters.
Nevertheless, even when using the same hop variety under the same
conditions (timing of addition and quantity), samples can have different
aroma intensities if fermentation is performed using different brewing
conditions (temperature, yeast pitching rate, etc.). Therefore, we
investigated the cause of differences in aroma intensities in order to
facilitate more precise control of hop aroma. We had the following two
hypotheses: “the extent of conversion of hop aroma by yeast varies
according to the brewing conditions” (hypothesis 1), and “hop aroma is
masked by compounds that are produced by yeast during fermentation”
(hypothesis 2). To test these hypotheses, samples that had different
intensities of fruity aroma (lychee, citrus-like), even though the same
hop variety (American Cascade and New Zealand Motueka) and hop addition
conditions were used, were subjected to GC/MS analysis to determine
whether there were any differences in the quantity of aroma compounds.
The results indicated that the amount of linalool and the amount of
beta-citronellol produced by the yeast did not significantly differ
between the samples. This suggests that the validity of hypothesis 1 is
low. Furthermore, as there was a difference in the amount of compounds
that arise from fermentation, hypothesis 2 appears to be valid. Next, we
investigated the influence of esters and alcohols on hop aroma. We
observed a tendency for alcohols (e.g., 1-heptanol) to mask fruity
aromas. Therefore, we brewed samples in which cold wort from the same
batch was fermented (in a 20 L scale fermentor) using different
fermentation conditions. Sensory evaluations revealed differences in
fruity aroma between samples. Statistical analysis indicated that there
was a significant negative correlation between 1-heptanol and fruity
aroma. Furthermore, 1-heptanol was positively correlated with the number
of yeast cells added at the start of fermentation and fermentation
temperature. These results further support hypothesis 2 and suggest that
it is important to control fermentation conditions. The results of this
research have lead to the establishment of specific brewing conditions
for more precise control of hop aroma.
Hitoshi Takemura has
worked for Kirin Brewery Company Limited since receiving a master’s
degree in life science from Kyoto University in 2002. He worked in the
Quality Assurance Department of the Tochigi brewery for three years and
then entered the Laboratory for Brewing, where he conducted research on
the use of hops in wort boiling. From 2008 to 2010 he worked as a guest
researcher in Lehrstuhl fuer Brau- und Getraenke Technologie fuer
Technische Universitaet Muenchen. Since August 2010 he has worked in the
Brewing Technology Development Center.
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