Hiromi Nishida

The co-cultivation of sake yeast (AK25, K901, K1401, or K1801 strain) and the kuratsuki Bacillus A-10 and/or Priestia B-12 strains in koji solution was performed to demonstrate the effects of these two kuratsuki bacteria on sake taste. The results showed that the Brix and acidity patterns of sake preparations produced with and without these kuratsuki bacteria were very similar. This indicated that the addition of these kuratsuki bacteria did not inhibit ethanol fermentation or organic acid production by sake yeast. A taste recognition device showed that the effects of these kuratsuki bacteria on the saltiness and sourness of sake were greater than those on other taste properties. Astringency stimulation and saltiness of sake produced using the sake yeast K901 were increased by Bacillus A-10 and decreased by Priestia B-12. Except for these two cases, the taste intensities of sake preparations produced with the Bacillus A-10 and Priestia B-12 strains were very similar, but differed from those of sake produced with kuratsuki Kocuria. These results support our hypothesis that the flavor and taste of sake can be controlled by utilizing the interactions between kuratsuki bacteria and sake yeast. For crating the desired sake taste, a combination of kuratsuki bacteria and sake yeast should be considered.

Koji is made using steamed rice and a koji mold, which plays an essential role in sake brewing. We challenge to build a new sake brewing method using the kuratsuki bacteria that have inhabited each sake brewery. In this paper, effects of the kuratsuki Kocuria strain TGY1127_2 were estimated on sake brewing in different koji conditions. Sake was produced by incubation of a mixture solution of koji, water, and sake yeast (strain K1401) with and without the kuratsuki Kocuria TGY1127_2. The effects of the kuratsuki Kocuria on the taste of the sake differed among different koji. The kuratsuki Kocuria led to an increase in ethanol concentration. Additionally, the sugar content (Brix) and acidity of the sake increased in proportion to the amount of koji. These results strongly suggest that the kuratsuki Kocuria does not adversely affect the fermentation activity of the sake yeast. Thus, the kuratsuki Kocuria had different effects on the taste of sake among different koji but the fermentation activity of the sake yeast was maintained.