Mechanism of High Alcoholic Fermentation Ability of Sake Yeast

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Sake yeast strains belonging to the budding yeast Saccharomyces cerevisiae exhibit higher rates of alcoholic fermentation and ethanol yields in the sake mash than the other types of S. cerevsiae strains. Although this has traditionally been regarded to be caused by their higher resistance against ethanol and various environmental stresses, recent studies revealed that they are rather defective in stress responses. Our genomic and transcriptomic approaches has led to the identification of the sake yeast-specific loss-of-function mutations in the MSN4, PPT1, and RIM15 genes, each of which has important roles in the responses to environmental changes. Surprisingly, each of these mutations contributes to the increase of alcoholic fermentation rate. Thus, we first reported the causal mutations for the high alcoholic fermentation ability of industrial yeast strains. These findings have drastically changed how we understand the relationship between ethanol tolerance and ethanol production ability of yeast cells. In this review, we introduce the history and progression of sake yeast studies, especially focusing on their superior alcoholic fermentation properties.