Effect of temperature on moromi fermentation of soy sauce with intermittent aeration

Soy sauce has been widely used as one of the main seasoning agents in Asian countries. Soy sauce is produced by two-steps fermentation processes, namely koji fermentation and moromi fermentation. In this study, different temperatures (25, 35 and 45°C) for moromi fermentation in bioreactor were investigated for understanding their influences on soya sauce quality, in terms of pH variations, ethanol concentrations and total nitrogen contents in raw soy sauce during moromi fermentation. It was learned that as the aging of moromi took place, the pH level was decreased from pH 7 to 4.88. Also, the soy sauce had lower concentration of ethanol when higher temperature was used in moromi fermentation but the difference of temperature did not show significantly effect on total nitrogen content in soy sauce. This study indicated that the temperature used in the moromi fermentation, coupled with intermittent aeration, imposed significant effects on soy sauce aging and quality. Higher fermentation temperature of 45°C enhanced the aging of soy sauce, accompanying with lower contents of ethanol and higher pH level in soy sauce. However, the total nitrogen content in the soy sauce was not significantly influenced by the fermentation temperature. Key words: Aspergillus oryzae, bioreactor, moromi, soy sauce, temperature.