STUDY ON THE CONTROL OF SHOCHU FLAVOR .2. FACTORS AFFECTING THE FORMATION OF ISOAMYL ACETATE DURING ALL-KOJI SHOCHU FERMENTATION

Greater formation of isoamyl acetate in 25-hour-cultivated rice-koji ( 25h-koji) mash than in conventional 43h-koji mash during all-koji shoc hu fermentation was estimated to be due to the following 4 factors. (1 ) Lower protease activity in the 25h-koji, which caused lower amino ac idity in the mash and increased the formation of isoamyl alcohol by th e yeast. (2) A lower content ratio of NH3 and a higher content ratio o f leucine in the 25h-koji, which contributed to isoamyl alcohol format ion. (3) A lower unsaturated fatty acid content in the 25h-koji, which supported the activity of the alcohol acetyltransferase of the yeast cells. (4) A larger number of viable yeast cells in the 25h-koji mash. As isoamyl acetate was not hydrolyzed in yeast-free mash, it is sugge sted that the esterase of rice-koji was not active in the shochu-mash.