Shortening Koji Cultivation Time Produces Fruity Aromas in Imo-shochu
Mr. Haoyu Zhu, a second-year doctoral student at the United Graduate School of Agricultural Sciences, had his research published in the peer-reviewed international journal “Food Bioscience” (Impact factor: 6.2) (published online on 14 May 2026).
In imo-shochu production, koji provides enzymes needed for fermentation and also affects the aroma and quality of the final product. Normally, white koji mold is grown on rice for about 43 hours, and the resulting koji, called “de-koji”, is used for fermentation. During koji making, important mixing steps are carried out at 19, 23, and 27 hours. However, it was not known how koji at these different stages affects the fermentation and aroma of imo-shochu.
In this study, four types of koji cultivated for 19, 23, 27, or 43 hours were used to produce imo-shochu. The researchers compared enzyme activities, amino acid use, aroma compounds, and sensory characteristics.
Imo-shochu made with 19-hour koji produced about twice as much higher alcohols and fruity esters, such as isoamyl acetate, as shochu made with 43-hour koji. It also showed stronger banana- and apple-like aromas in sensory evaluation, while the 43-hour koji produced a more typical imo-shochu aroma.
These results show that changing the koji cultivation time can alter yeast metabolism and the aroma of imo-shochu. In particular, shorter cultivation may be a useful way to produce imo-shochu with distinctive fruity aromas and to develop a wider variety of products.
■ Publication Information
Title: Koji maturation dynamics regulate enzymatic activity, amino acid metabolism, and aroma formation across fermentation in imo-shochu
Authors: Haoyu Zhu, Yumiko Yoshizaki, Mizuki Watanabe, Yuta Anan, Taiki Futagami, Hisanori Tamaki, Kazunori Takamine
Journal: Food Bioscience
