Characteristic odour compounds in shochu derived from rice koji

Shochu, a traditional Japanese distilled liquor, makes use of rice koji, which is koji mould grown on rice grain. Rice koji is an essential ingredient of Japanese liquors such as shochu, and it plays a role as a source of the enzyme to degrade starch. However, there has been no research on the effect of rice koji on the flavour of shochu. Therefore, in this study, the volatile compounds in shochu derived from rice koji were investigated. Two shochu samples were prepared to assess the contribution of rice koji to the flavour. One shochu sample was prepared from rice koji, yeast and water (rice koji-shochu). The other shochu sample was obtained from steamed rice and various enzymes instead of rice koji (enzyme-shochu), along with yeast and water. The volatile compounds were analysed by gas chromatography–mass spectrometry (GC-MS) and GC-MS/olfactometry with aroma extract dilution analysis. The results showed that enzyme-shochu had a higher flavour dilution value of dimethyl trisulphide and hexanal, whereas rice koji-shochu had a higher flavour dilution value of some ester compounds that imparted aromatic odours such as fruity. Some unknown peaks representing compounds that impart characteristic odours such as soda, potato, lavender, and tea-like were specifically detected in rice koji-shochu. The concentrations and calculated odour active values of 14 compounds were measured. These results showed that isovaleraldehyde, ethyl caprylate, ethyl caproate and ethyl 2-methylbutyrate played an important role in imparting the specific odour of rice koji-shochu. Copyright © 2016 The Institute of Brewing & Distilling