Dandan Wei (1),
Misa Tanaka (1), Saori Takahashi (1), Kentaro Iwasaki (1), Hironori
Inadome (1), Satoshi Yoshida (2), Hiroyuki Yoshimoto (1); (1) Research
Laboratories for Alcoholic Beverage Technologies, Kirin Company,
Limited, Namamugi, Tsurumi-ku, Yokohama, Japan; (2) Central Laboratories
for Key Technologies, Kirin Company, Limited, Japan
Yeast, Fermentation, and Microbiology
Poster
In beer, the composition of terpene alcohol is strongly influenced by
the type of hops used in the brewing process. Yeast cells are able to
convert the monoterpenoid geraniol to beta-citronellol during the
fermentation process. We have approximately 1,100 yeast strains in our
yeast bank, which includes beer yeasts, sake yeasts, wine yeasts and
whiskey yeasts. After collecting the various yeast strains in our
fermentation experiments, we compiled a database of our yeast bank to
collate the flavor and the brewing characteristics of the yeasts in the
database. In the present study, we attempted to identify yeast strains
with the ability to efficiently convert geraniol to beta-citronellol by
monitoring for beta-citronellol production. Furthermore, to increase the
sweetness of the finished product, the brewing conditions that
increased residual maltose levels were investigated. The production of
beta-citronellol by a total of 114 yeast strains (shochu, wine, and
top-fermenting yeast strains) was evaluated by performing fermentation
experiments in 10 mL test tubes with the bottom-fermenting yeast strain
KBY011 as a control. Yeast strains identified as having high
beta-citronellol production ability were further evaluated in larger
scale fermentations of 500 mL, 20 L, and 200 L. Two strains, wine yeast
strain WIY40 and top-fermenting yeast strain TFY192, were found to
produce beta-citronellol levels that were threefold higher than that of
the control yeast strain KBY011. As strain WIY40 was determined to
produce beer with the best balance of flavors, we used this strain to
investigate the optimal brewing conditions for increasing residual
maltose levels as an approach for producing beer with higher sweetness.
By adjusting the sugar composition enzymatically in wort, the optimal
ratio of monosaccharide to maltose that allowed maltose consumption to
be delayed was determined. In addition, rapid cooling of the optimized
wort resulted in sufficiently high residual maltose concentrations.
Thus, by combining a yeast strain with a high
beta-citronellol–converting activity, wort with an optimal sugar
composition, and rapid cooling during the fermentation process, beer
with an enhanced citrus flavor, natural sweetness and reduced bitterness
could be produced. These findings demonstrate that the combined use of
wine yeast and optimal brewing conditions is capable of adding a citrus
flavor and sweetness to beer, without the requirement for additional
hops or sugars.
Dandan Wei received a master’s degree in agriculture from Kyoto
University, Japan, in March 2011. She was employed in April 2011 by the
Brewing Technology Development Center, Kirin Brewery Company Ltd., to
conduct research on yeast. She also studied brewing technology at the
University of California, Davis, from January to April 2015. The
organization of Kirin Brewery Company changed in January 2013, leading
to the current Kirin Company Ltd.
