Presenter: Shinichiro Yamamura, Suntory Liquors Limited,
Ohra-gun, Gunma, Japan
“Metallic flavor” is a metal-like flavor that gives the impression
of rusty iron or of a can. This flavor is easy to detect in beers
with a light taste, such as third-category beers, and it is a factor
that negatively impacts beer quality. Third-category beers
have been rapidly expanding in the Japanese beer market,
and the ratio of sales is about 35%. Therefore, it is an urgent
task for us to improve metallic flavor. Based on a previous
study, it was known that the substances causing metallic
flavor are 1,5-octadien-3-ol and its oxide 1,5-octadien-3-
one, which are oxides from an unsaturated fatty acid derived
from raw materials. Our attempts to reduce metallic flavor
could not proceed, however, because we did not know how
the substances are generated. We analyzed a product that
was judged as having a strong metallic flavor in our sensory
evaluation. It was confirmed that this product had a high iron
concentration in the beer. Based on this fact, we performed an
iron addition experiment to elucidate the mechanism generating
the metallic flavor. From this, we developed the hypothesis
that it is necessary to reduce the unsaturated fatty acid and
iron concentrations in the beer to improve metallic flavor. We
tried to reduce wort turbidity during the lautering process to
decrease the unsaturated fatty acid, because it had already been
reported that there is a correlation between wort turbidity and
the concentration of the unsaturated fatty acid (Kühbeck et
al., J. Inst. Brew. 112:222-231, 2006). We also tried to reduce
the amount of kieselguhr to decrease the iron concentration,
because kieselguhr includes some iron. As a result, we were
able to reduce the substances causing the metallic flavor and
to improve the sensory evaluation score dramatically. We also
carried out a sensory evaluation after eating various foods and
consuming beers with high and low iron concentrations. When
there were high concentrations of iron, a metallic flavor could
be detected in reaction to the unsaturated fatty acid derived
from the food. From this result, we could prove our metallic
flavor hypothesis.
Shinichiro Yamamura is an assistant brewmaster in the
Suntory Tonegawa brewery. The main subject of his work is
development of brewing technology. He majored in molecular
biotechnology at Hiroshima University, and he was engaged in
elucidation of molecular mechanisms of mouse olfactory. He
joined Suntory Ltd. in 2010. He is now engaged in improving
beer quality and development of brewing technology.
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