Properties of Yakju and pellet Nuruk inoculated with Aspergillus oryzae

Aspergillus oryzae 83-10 (AO) was inoculated in a wheat pellet with different concentrations of raw materials to produce Nuruk. The sterilized raw material (S) was found to be stable in the production of pellet-Nuruk and was suitable for the production of high enzyme power; high enzyme activity was obtained after fermentation for 32 h. The characteristics of pellet-Nuruk were investigated and the brewing characteristics were compared with those of the commercial SongHak (SH) Nuruk. The enzyme activities (dry base, unit/g) of S-AO (sterilized material and inoculated with A. oryzae) pellet-Nuruk (32 h culture) and the commercial SH Nuruk were compared. The activities of glucoamylase, α-amylase, and acidic carboxypeptidase were significantly higher in S-AO Nuruk. In terms of brewing characteristics, the soluble solid (°Brix) and total acid (%) were significantly higher in the SH mesh, and the amino acid content and alcohol content (%) were significantly higher in the S-AO mesh. The amount of Nuruk added for yakju fermentation was set at 30 unit/g × g of rice weight based on the glucoamylase activity. The enzymatic activity immediately after preparation was 26.69 unit/mL and 17.58 unit/mL for S-AO and SH, respectively. Based on these results, preparing pellet-type Nuruk should considerably save fermentation time compared with traditional Nuruk products.