Made of cooked rice and/or soybeans that have been injected with the culture Aspergillus oryzae and left to ferment, koji is central to Japanese cuisine, used to make everything from miso to shoyu. And as the co-chef of Bar Tartine in San Francisco, where we focus on all kinds of fermented ingredients, koji has become an essential part of my pantry.
My koji fixation hit me about five years ago, when I was working part-time at the Culinary Institute in St. Helena, California. That year, the Institute's annual autumn food conference, World of Flavors, focused on Japan. I was in awe of so many Japanese chefs under one roof that I decided to try making koji myself. The effort took me 48 hours and left me in near tears from both excitement and exhaustion, but eventually I had made an enticing batch of sweet bacteria-inoculated rice that left me hooked.