Technical Session 03: Yeast I Session
Yuichi Nakamura, Asahi breweries, LTD.
Co-author(s): Hisao Koizumi, Asahi Breweries, Ltd., Japan
ABSTRACT: According to the results of our previous report,
the impact of the wort aeration period of multi-filling CCVs, presented
at Brewing Summit 2010, we changed the ways to pitch yeast and aerate
wort. In our breweries, four batches of wort are filled in a 5,000 hL
cylindroconical vessel. In the process before the change, the same
amount of yeast and air were pitched into the first to fourth batches of
wort. As for the improved process, yeast and air were pitched into the
first, second, and third worts, while neither yeast nor air was injected
into the fourth wort, which was just transferred to the fermentation
vessel. Though this improvement raised the sensory scores as expected,
the specific gravity and the number of yeast cells of the fermenting
beer were largely different from the data before improvement. Therefore,
we developed new equipment capable of sampling the fermenting beer at
four different heights in a fermentation tank and installed it on the
5,000 hL tank in our brewery. (Detailed specifications of the equipment
are separately reported by our colleague Hisao Koizumi.) Under the
previous conditions, the temperature, yeast cells, specific gravity, and
amino nitrogen of the fermenting beer were the same at all four
different heights. In the case of the improved method, the bottommost
layer and the upper three layers of the fermenting beer were not
blended, and fermentation proceeded as each layer remained independent.
After 50–60 hr from initiation of fermentation, convection was
generated, and the 5,000 hL of fermenting beer became homogeneous. At
the time just before the fermenting beer was blended, the bottommost
layer contained a rich amount of remaining amino acids and
monosaccharides. Meanwhile, these amino acids and monosaccharides had
already been consumed and depleted in the upper three layers. When the
entire fermenting beer in the fermentation vessel was blended after
50–60 hr of fermentation, the nutrients remaining in the bottommost
layer, such as amino acids and monosaccharides, were supplied to the
upper layers. According to the flow cytometry results on yeast budding,
the bottommost layer beer before blending contained a larger percentage
of currently budding yeast cells. These results suggested that the
bottommost layer beer contained many yeast cells under nutrient-rich
conditions that were highly active and currently budding, and such
highly active yeast cells were then diffused throughout the entire
fermentation tank at approximately 50–60 hr. We therefore concluded that
fermentation steadily proceeded to the end without reducing the rate,
and thus the beer flavor and taste were improved and stabilized.
Yuichi
Nakamura received an M.S. degree in agricultural chemistry from Tokyo
University, Japan. He began employment with Asahi Breweries, Ltd. in
April 1993. After working as a researcher in the laboratory, he was
transferred to the brewing section of the Ibaraki brewery. He studied
brewing technology at TU Muenchen-Weihenstephan in Germany for one year
from 2001 through 2002 and returned to the Nagoya brewery. He has been
working in the Production Technology Center, Asahi Breweries, Ltd. since
2005.
VIEW PRESENTATION 8
