Shoyukoji is technically the base of soy sauce in the production process (see Kikkoman website). However, today the term is more commonly used to mean a mixture of shoyu soy sauce and koji rice malt, which has become popular in the last few years in Japan and among the Japanese community overseas. Just like shiokoji salted rice malt, shoyukoji is full of umami. In fact, its glutamic acid content is said to be 10 to 15 times of that of shiokoji.
