Korea National College of Agriculture and Fisheries

The production of distilled soju by fermenting nonsteamed rice was evaluated using commercial enzyme products. White koji and modified nuruk had alpha-amylase activities of 31.90 U/g and 3,532.71 U/g, respectively, and gluco-amylase activities of 698.32 U/g and 4,899.58 U/g, respectively. The enzyme products had activities of 5,604.15-225,182.00 U/g and 13,517.41-120,822.41 U/g, respectively. At enzyme concentrations of >800 mg/L, the Chung-moo-purified enzyme had an alcohol productivity of ≥19%. Nurukzyme R400, Sanferm Yied, and Diazyme X4 exhibited alcohol productivities of >19% at concentrations of >600 mg/L. The alcohol content of the vacuum distillates was 41.31%-44.86%. The volatile component with the alcohol content adjusted to 25% was analyzed and principal component analysis was performed. The volatile components in white koji, Diazyme X4, and Sanferm Yield were similar. The modified nuruk treatment group had a relatively high ethyl lactate content compared to the white koji treatment group. The Nurukzyme R400 treatment group had high contents of butyric acid and ethyl butyrate. The Chung-moo-purified enzyme was characterized by a low component content. Thus, when enzyme products were used in nonsteamed rice fermentation, no effect on the alcohol productivity and quality of vacuum distilled soju was observed, suggesting that it can replace white koji and modified nuruk.

This study aimed to investigate the effect of using a combination of ipguk (koji) and zeolite, as an alternative to the traditional nuruk fermented agents and rice and rice husks combination, on off-flavor suppression in solid fermented spirits. In alcohol production from solid fermented mash, the traditional brewing combination (nuruk + rice husks) produced over 1.3 times more alcohol than that obtained using the alternative combination (ipguk + zeolite). The levels of acetic, butyric, isovaleric acids, and methyl mercaptan, the components causing the offensive odor of distilled liquor (25% alcohol), were significantly reduced upon using the alternative combination as compared to that by the traditional combination. The acetic acid level decreased from 99.38 mg/L to 19.34-24.12 mg/L when using the alternative combination. Butyric acid, isovaleric acid, and methyl mercaptan levels decreased from 95.90, 5.37, and 426.78 mg/L, respectively, to undetectable levels. The furfural content decreased up to 4.3 times. In contrast, acetaldehyde levels increased from 228.04 mg/L to 529.74-578.71 mg/L when using the alternative combination. As the moisture content of the solid-fermented mash prepared with the alternative combination increased (from 40 to 55%), the alcohol production also increased proportionally, and the alcohol content of the distillate was elevated (from 37.14 to 43.74%).