Mirin-Making from Koji Prepared with a Mutant Aspergillus oryzae Producing High Activity of Carboxypeptidase☆

Abstract It has been desired to improve the quality of mirin without decreasing the level of productivity. Accordingly, by ultraviolet irradiation to cause mutation, we screened for mutants with high acid carboxypeptidase (ACPase) activity from Aspergillus oryzae IFO 4079 (parental strain). We obtained a mutant with ACPase with the activity of 20,000 units · g −1 of koji , about three times that of the parental strain. In mirin -making, koji prepared with this mutant had the same productivity, but the concentration of amino nitrogen in the mirin obtained with this mutant was 1.2–1.4 times that of the parental strain. Results of sensory tests showed that the mirin prepared with koji of the mutant had a good taste on the whole. The degree of clouding In mirin made with glutinous rice steamed at atmospheric pressure was much less with koji of this mutant than that of the parental strain.