In sake brewing, rice starch is saccharified utilizing enzymes produced by a koji mold (Aspergillus oryzae), and the resultant glucose is fermented into ethanol by sake yeast (Saccharomyces cerevisiae) (1). Over hundreds of years of sake brewing, brewers in Japan have selected yeast strains based on ethanol production and on favorable characteristics of the final product, such as a high ethanol concentration and an appetizing flavor (1). As a result, brewing sake produces a beverage that has the highest concentration of ethanol of all industrial brewing processes in the absence of distillation. Indeed, the final product often has more than 20% (vol./vol.) ethanol. With the current interest in improving the efficiency of industrial ethanol production, there is also strong interest in research into understanding why sake brewing results in such a high concentration of ethanol.