Formation mechanism of ethyl ferulate (EF) in sake and mirin mash conditions was investigated to understand EF
level control in the manufacturing process. Rice koji formed EF from ferulic acid (FA) and ethanol and decomposed EF to
FA. This did not occur in sake yeast and chemical esterification was rare. Esterification of FA and hydrolysis of EF by rice
koji might be due to feruloyl esterase(s). The rice koji enzyme showed normal MichaeliseMenten kinetics for FA in ethyl
esterification and for EF in hydrolysis, but not for ethanol in the esterification reaction. Substrate specificity of the rice
koji enzyme for hydroxycinnamic acids suggested that the main enzyme involved might be similar to type A feruloyl
esterase. We studied the rice koji enzyme properties, short-term digestion of steamed rice grains with exogenous
ethanol and small scale mirin making with pH adjustment. Our results suggested differences in the esterification and
hydrolysis properties of the enzyme, in particular, different pH dependencies and different behaviors under high
ethanol conditions; these factors might cause the differing EF levels in sake and mirin mashes