Factors that cause replacement of shochu yeast by wild yeast upon Sashi-moto repetition.

In shochu-making, a small amount of fermenting moromi is added to a koji/water mixture instead of yeast culture to initiate fermentation. This is a characteristic process called Sashi-moto. It is known that shochu yeast is replaced by wild yeast upon repetition of Sashi-moto. The shochu yeast strains Kagoshima No. 2 (K2), Kagoshima No. 4 (C4), and Kagoshima No. 5 (H5), but not Kagoshima No. 6 (A6), were replaced by wild yeast (strain No. S5-g). K2 and C4 were easily replaced compared to H5, and the specific growth rates of K2 and C4 were lower than that of S5-g under higher osmotic pressure. Although the specific growth rate of H5 was higher than that of S5-g, its yeast population at the stationary phase was smaller than S5-g. On the other hand, both the specific growth rate and yeast population of A6 were higher than those of S5-g. The specific growth rate of yeast would be affected by osmotic tolerance and specific characters of the yeast strain.