Co-cultivation of sake yeast and Kocuria isolates from the sake brewing process

Kuratsuki bacteria and sake making

Kuratsuki bacteria enter during the sake-making process and interact with sake yeast until their growth is attenuated by the ethanol produced by sake yeast. Due to the interaction between kuratsuki bacteria and sake yeast, the metabolism of sake yeast changes, affecting the composition of esters and organic acids and subsequently the flavor and taste of sake. We cultivated kuratsuki bacteria and sake yeast, and performed test making at sake breweries to clarify the interaction among microorganisms in the sake-making process. We aim to propose a sake-making process that controls the flavor and taste of sake by utilizing the functions of kuratsuki bacteria.

Effect of kuratsuki Kocuria on sake's taste varies depending on the sake yeast strain used in sake brewing

Although sake yeast mainly produces the taste of sake, sake brewery-inhabiting (kuratsuki) bacteria affect the taste of sake. Thus, kuratsuki bacteria may alter the metabolism of sake yeast through interactions between kuratsuki bacteria and sake yeast. This study aimed to confirm the effects of the combination of kuratsuki Kocuria TGY1127_2 and different sake yeast strains, AK25, K901, and K1801 on the taste of sake. Although the Brix and acidity during sake production using AK25 differed between sake with and without kuratsuki Kocuria, those using K901 and K1801 did not differ. Thus, sake yeast AK25 interacted with kuratsuki Kocuria and changed its characteristics of ethanol fermentation. In addition, the taste intensity changes, measured with a taste sensor TS-5000Z, showed that the effects of adding kuratsuki Kocuria varied among different sake yeasts. Thus, each sake yeast strain interacted with the kuratsuki bacterium and produced different metabolites, resulting in a change in the taste of sake. The findings of this study can lead to the brewing of sake using different types of kuratsuki bacteria which can affect the taste of sake.

Diversity of Bacillus Isolates from the Sake Brewing Process at a Sake Brewery

We collected 92 isolates belonging to the genus Bacillus from the sake brewing process at Shiraki Tsunesuke Sake Brewery in Gifu, Japan to determine whether there is strain specificity at individual sake breweries. After distributing the isolates into seven groups, we observed that at least two groups (68 isolates) were kuratsuki bacteria at Shiraki Tsunesuke Sake Brewery. The kuratsuki Bacillus isolates were collected from different samples at the early and late stages of sake brewing in 2021 and 2019, respectively. These results showed that kuratsuki Bacillus entered the sake brewing process at this location. These kuratsuki Bacillus isolates had a high ethanol tolerance. Our previous paper showed the existence of kuratsuki Kocuria at Narimasa Sake Brewery in Toyama, Japan, but this study demonstrated that it is not found at Shiraki Tsunesuke Sake Brewery. Therefore, each sake brewery has specific kuratsuki bacterial strains, which are isolated with high frequency and contribute a specific flavor or taste to each sake brewery.