Yeast and Fermentation Session
Yasuhiro Muraoka, Frontier Laboratories of Value Creation, SAPPORO BREWERIES LTD., 10 Okatohme, Yaizu, Shizuoka, 425-0013 Japan
Co-author(s): Masahide Sato and Tatsuro Shigyo, Frontier Laboratories of Value Creation, Sapporo Breweries Ltd., Yaizu, Japan
ABSTRACT: Premature yeast flocculation (PYF) refers to the
phenomenon whereby yeasts flocculate prematurely during fermentation in
the presence of high sugar concentrations. PYF is considered to be
induced by so-called premature yeast flocculation inducing factors in
malts, although the structure and the mechanism of how they cause PYF is
unclear. It is very important for brewers to detect malts that cause
PYF because it leads to low attenuation and results in an undesirable
flavor in beer. In order to estimate the potential of malts regarding
PYF (PYF potential), several methods have been developed in the past.
However, these methods are time-consuming; they take 2 days to 1 week to
complete the fermentation tests. In this report, we developed a new
method for evaluating the PYF potential more effectively using 180 mL
scale fermentation. In our method, the floating cells were measured by
counting yeast cell numbers or by measuring the optical density of
suspensions during fermentation. We prepared wort from malts having or
not having PYF potential, performed fermentation, and compared the
degree of flocculation. As a result, we were able to evaluate the PYF
potential only after 24 hr of fermentation, which remarkably shortened
the assay period. We expect our method to be useful for predicting the
PYF potential of malts and enabling us to prevent PYF in brewing and to
improve beer quality.
Yasuhiro Muraoka received an M.S. degree
in biological sciences from the Nara Institute of Sciences and
Technology. He joined the Hokkaido brewery of Sapporo Breweries Ltd. in
2005 as a brewing engineer. Since 2010, he has been working in Frontier
Laboratories of Value Creation as a research brewer.
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