Citric acid
Japanese: クエン酸
An organic acid abundant in citrus fruits. Produced in large quantities by white and black koji molds, it prevents contamination in shochu production.
Citric acid is an organic acid well known as the sour component of lemons and grapefruits. Named in the TCA cycle (citric acid cycle), it is a central molecule in metabolism.
White koji mold (Aspergillus kawachii) and black koji mold (Aspergillus luchuensis) characteristically produce large amounts of citric acid. These molds are used in shochu and awamori brewing because citric acid lowers the mash pH, preventing contamination. In warm Kyushu and Okinawa, this property has long ensured brewing safety.
Yellow koji mold (Aspergillus oryzae) produces almost no citric acid. Even within koji molds, different species produce different metabolites, creating different applications.