Treatment of sake with immobilized cells of Aspergillus oryzae was carried out to remove offflavors. Conidiospores of A. oryzae were immobilized in 2% sodium alginate gel, followed by incubation in koji extract at 30° with or without shaking for 1-3 days. Thus, immobilized cells containing 1.5-12 mg mycelium per gram gel were prepared. Immobilized cells were added to sake containing off-flavors in an amount 40 gram per 200 ml sake, and left at room temperature. Acetaldehyde smell, and “kiga” smell, which is a kind of woody smell derived from cedar, as well as “hineka” smell, which occurs through over-maturation during storage process of sake making, were efficiently removed. Besides, the occurrence of moldy smell, which is a kind of off-flavor derived from cells of A. oryzae, was prevented by the immobilization. The mechanism of removal of acetaldehyde smell was also studied, and it was found that acetaldehyde was reduced to ethanol by immobilized cells.
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