Evaluation of koji prepared with various molds for mirin-making

Abstract Koji is one of the raw materials used for mirin -making, and it is traditionally prepared with Aspergillus oryzae . To improve productivity and to be available for a variety of mirin , various koji were prepared with A. niger, A. awamori, A. usamii mut. shiro-usamii , and Rhizopus oligosporus and examined for possible to use in mirin -making. The degrees of digestion of the starch and protein in various koji were at its highest with either koji prepared with A. oryzae at pH 7.0 or with A. usamii mut. shiro-usamii at pH 3.0. The degree of digestion of the protein in koji made with A. usamii mut. shiro-usamii was decreased in koji digestion at higher temperature (at over 50°C) compared to that in koji made with A. oryzae . We examined the ratio of koji to steamed glutinous rice to identify the optimum value for mirin production. The optimum ratios for digestion of starch in the mash with koji of A. oryzae and A. usamii mut. shiro-usamii were 0.10 and 0.15, respectively. These values were in agreement with the 0.10–0.25 established by experience. Therefore, of the five strains tested, A. usamii mut. shiro-usamii , among the tested molds was the most suitable strain for preparing koji in mirin -making without decreasing productivity, while lending new qualities to the mirin . The koji prepared with A. oryzae had a good smell but the koji prepared with A. usamii mut. shiro-usamii had a little mold smell. Then if this little mold smell could be improved, this koji can be used in mirin -making. The koji prepared with A. niger contained the most citric acid of all strains but the digestivities of starch and protein in the koji was less than those of koji prepared with A. oryzae and A. usamii mut. shiro-usamii . The digestivities of starch and protein in koji prepared with A. awamori were the lowest values. In 35% alcohol, its productivities in mirin -making seemed to be low. Because of the highest content of lactic acid, the koji prepared with R. oligosporus seemed to be suitable for mirin -making. Then if its productivity could be improved, this koji can be used in mirin -making.