Studies on Wild Sake Yeasts

Part 4 The relation between thik yeast cover forming yeasts and the fermentation on mash

Abstract

In the previous papers, it was found that most of the wild sake yeasts aggregated with the cell walls of rice starch granules, formed a thick yeast cover and indicated less attenuation at the end of fermentation of the mashes.
Studies were carried out with two types of sake yeasts, a thick yeast cover forming strains-A-63, 8-23, etc. and good dispersing yeast strains Kyokai No.7, No.9, etc. and the following results were obtained.
(1) Among the two types of yeasts, there were no differences in QCO₂ by Wahrburg's method and in the rate of fermenting Koji-extract. In sake mash, however, the thick cover forming yeasts indicated incomplete fermentation.
(2) At the end of fermentation of the mashes fermented by each of the two types, the viable counts of A-63 and S-23 were less than that of Kyokai No.7 strain.
(3) When A-63 strain cultured in Koji-extract for 10 days was mixed with the same rate of cell number of Kyokai No.7 strains at the end of the mash, the colony counts of A-63strains was found to be less than that of No.7 strain in a ratio of about 1 to 9.
It was found from the above results that the various phenomena mentioned above occur because the strains forming the thick yeast cover aggregate with the walls of rice starch and separates from the fermentation system when fermenting mash-like highly flocculative brewer's yeasts.