Koji has long been used in Japan to make soy sauce, sake, miso and other traditional foods. Now, this ancient fermented ingredient is trending on both sides of the Pacific as restaurant chefs and home cooks see it as a convenient source of flavor-boosting umami, which is often described as a sense of savoriness.
"It is a very old naturally fermented food, that's gotten very popular in Japan in recent years as a natural source of umami as well as beneficial flora for your digestive system," writes Makiko Itoh, a food writer and blogger. "It's great to use in marinades for meat, poultry or fish."
Koji comes in varieties including salt, soy and sweet. Itoh uses salt koji to create a quick sauce from canned tomatoes. It "enhances the umami in the tomatoes and gives the sauce a 'meaty' flavor without adding any meat," she writes.