Comparative characteristics of rice wine fermentations using koji and rice nuruk.

Wine fermentations using rice media containing either koji or rice nuruk were performed and fermentative characteristics based on the koji type were investigated. Cultivations were performed in a 20 °C room in a 20 L bottle with the rice media that included rice koji at both 20 and 30%, or rice nuruk at 20%. After 22 days of cultivation, the ethanol yield reached 14.2-14.6% (v/v) for koji and 16.5% (v/v) for rice nuruk. This lower yield with use of koji was thought to be due to rapid cell concentration decreases in the later stage. Total amounts of organic acids and volatile compounds in fermentations using koji were 166-172 and 1779-1874 mg/L, respectively, being 8.7-12.9% and 46.3-54.1% higher than with use of rice nuruk. With koji, a high quality rice wine was produced with high levels of volatile compounds and monacolin K.