Making your own koji is extremely rewarding. It takes patience and some tending over the 40+ hour fermentation period, but once you witness the the beautiful mold develop, you'll be hooked! This recipe guides you through a basic rice koji but you can grow koji on other grains similarly.
3 cups (525 g) of medium to long grain white rice
2 tablespoons (20 g) of white rice flour (gluten-free option) or all-purpose flour
1 teaspoon (1 g) of koji spores
Steamer or pot to cook rice
Small sauté pan
Lint-free flour sack towel
Tray or sheet/baking pan (that fits your incubation chamber)
Incubation chamber (like our Brød and Taylor proofer) to maintain temperature between 81-95 F
Rinse your rice well and soak it in water for at least 6 hours. Drain the rice for 30 minutes and then steam or cook your rice until it's al dente. You want the rice to maintain its shape, yet be pliable. We recommend using a bamboo steamer lined in a lint-free cloth, which takes about 50-60 minutes to steam. While your rice is cooking, heat the flour in a small, dry sauté pan to sterilize it. Let the flour cool down to room temperature and add the koji spores, stirring to disseminate.
Once your rice has finished cooking, transfer to a lint-free towel and spread it out into about a 1-inch thick layer until it cools to below 110 F. Sprinkle half of the koji-flour mixture over the rice and fold it in gently. Sprinkle the remaining mixture on top and fold it in for another minute or two ensuring it's well distributed. Break up any clumps of rice that have formed as you go. Gather the edges of the towel together forming your rice into a neat bundle inside, and hold the towel together with a rubber band. Stick a thermometer through the opening so that you can keep an eye on the temperature. Place your bundle into your incubation chamber, using more towels if necessary to help insulate.
You want to maintain an internal rice temperature between 81 - 95 F. If using the Brød and Taylor proofer, set it to 85 F. Check on your koji every 2-4 hours throughout the day making necessary adjustments to your incubation set up to maintain this temperature. Prolonged overheating above 100 F will kill the koji mold and bacteria will take over.
After about 24 hours you will start to smell a slightly sweet, mushroomy smell. You should start to see what looks like a faint white dusting on the rice. At this point, unbundle your rice and spread the towel and the rice out flat in an even layer on your tray. You may have noticed that the temperature of the koji was starting to increase on its own. This is because the fermentation has started to generate its own heat. Create furrows about half an inch deep and an inch and half apart across the entire surface using your fingers to help reduce the risk of "hot spots". Return your thermometer into the rice and cover with a slightly damp towel to keep in the moisture. Check the koji every 4 hours or so, ensuring the temperature doesn't drop or rise too much. You're goal is still 81 - 95 F. If it continues to rise, you can stir it quickly to break up lumps, level it out, and add back the furrows and moist towel before replacing it in the incubation setup. You can also decrease the incubator temperature, vent the incubation chamber, or turn it off entirely.
After about 40 hours (or up to 50), you should start to see a white mold all over the grains. Break several of the grains to check for their maturity. They should break easily and the chalk-like whiteness should comprise more than half of the grain's diameter.
Your koji is ready for use immediately! We recommend using koji while it's fresh. Alternatively, you can freeze it (after bringing it down to room temperature first and then chilling it in the fridge) for up to 6 months or dehydrate it at 95 F or below for longer term storage.
See our step by step instructions above in our Instagram Stories.
Recipe and photos by Julia Street.