O-17
Development of a highly sensitive method using flowcytometer for evaluation
of yeast vitality and its application to yeast-handling technology. It is a fact among brewers that vital yeast leads to the highest-quality
beer; thus, it is essential to be able to measure yeast vitality precisely. A
number of researchers have developed various methods to do so; however, all of
these conventional methods carry a potential defect: only the mean vitality of
cell mass (i.e., of the cell population) is focused on. Equally significant as
the mean value is the distribution of vitality among the population (this is
similar to the estimation of malt quality, where both modification and
homogeneity are important). Differences in the distribution of the pitching
yeast can influence the fermentation performance of the yeast, and thus the
quality of the finished beer. In light of the above, we have developed the new
intracellular pH measuring method using the flowcytometer, enabling us to
measure true yeast vitality and providing highly-sensitive, instant analysis of
the distribution of individual cell vitality. We have applied this new approach
to the optimization of yeast-handling technology. First, we evaluated the
effects of impurities in the harvested yeast (referred to below as "Decke") on
yeast vitality using this method, effects that have long remained unclear in the
field of brewing science. In the laboratory, using several vitality tests, the
removal of "Decke" from harvested yeast through the use of sieves was shown to
maintain yeast vitality during storage. Moreover, regarding yeast vitality
during storage, yeast samples are first divided into two groups--lower and
higher yeast vitality groups. Then the samples of the higher group gradually
tend to shift lower one. The effect of removal of "Decke" is to slow the
above-mentioned shift speed. It is clear that this new method, using the flowcytometer
to evaluate yeast vitality, represents a novel technique, not only for the
optimization of yeast-handling methods, but for monitoring the state of yeast
vitality during storage, a new application of which we were previously unaware.
Jiro Nagai was born in 1974. He received both his B.Sc. and
M.Sc. degrees in fermentation technology from Hiroshima University in Japan.
After graduating from Hiroshima, he joined Kirin Brewery Co. Ltd. in 1999. From
1999-2001 he worked in the Toride plant as a staff member in brewing production.
Since 2001 he has worked at Brewing Research Laboratories. His area of research
is impact of technology on yeast and fermentation.
JIRO NAGAI, Motoo Ohkochi, Takeo Imai, Haruhiko Arimura, and Mayumi Suzuki.
Kirin Brewery Co., Ltd., Yokohama, Kanagawa, Japan.