From kombucha and kimchi, to sauerkraut and kefir, fermented foods are becoming more and more commonplace in restaurants, grocery stores, and even home kitchens. But one that might not be very familiar is koji rice. Maybe that’s because it’s a fermented food that’s hiding inside another fermented food you have in your pantry right now! Koji rice is cooked rice that has been inoculated with Aspergillus oryzae, a mold that’s widespread in Japan.