Effects of ipguk (koji) and zeolite combination on odor component suppression and alcohol productivity of solid-fermented spirits

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%).