Koji is a mold that is at the heart of many different Japanese ferments. It is used to make miso, sake, amazake, rice vinegar, soy sauce and mirin. Koji is grown on rice or barley, which are then used as the starter culture for further fermentation.
Making homemade koji is quite straight forward. The most difficult part of making homemade koji is finding the koji spores (koji-kin). You may be able to find koji-kin in your local Japanese grocery store or you can buy it online. Just make sure that it’s koji-kin, not koji rice.
Once you have koji spores in your freezer, making koji rice or barley is fairly simple.Print
Homemade Koji Rice
Koji rice (and koji barley) is used to make miso, sake, amasake, rice vinegar, soy sauce and mirin. Learn how to make homemade koji rice by growing koji kin mold on rice.
- Prep Time: 15 minutes
- Cook Time: 15 minutes
- Total Time: 30 minutes
- Yield: 4 cups 1x
- Method: Fermented
- Cuisine: Japanese
- Diet: Vegan
- 2 cups rice (white or polished brown)
- 1/4 tsp koji-kin culture (see notes)
- Rinse the rice until the water runs clear (to remove all the starch).
- Soak the rice in water for 8-12 hours.
- Steam (not boil) the rice until it’s softened, but still sticky (see notes for advice).
- Cool the rice to room temperature.
- Thoroughly mix the koji-kin culture into the rice.
- Spread the rice out on a baking dish. Cover with a damp cloth (to keep it moist but not wet) and maintain at 90 F (30 C) for 48 hours.
- Stir every 12 hours to break up the clumps and evenly distribute moisture. After 48 hours, white mold fibres should have started to develop. Stop at this point or it will spore.
- Store koji rice in the freezer until you are ready to use it.
- See below for incubation options and to learn how to save your own koji-kin mold spores for future batches.
- Since this is a mold ferment it’s important to keep everything clean.
- For koji barley, use pearled barley instead of rice and follow the same procedure.
- For steaming, I recommend using a vegetable steamer or colander lined with a tea towel. Just boil the tea towel in the steamer to sanitize it before using it to steam your rice.
- Make sure you buy your koji kin from a reputable source. I recently heard from a reader who bought koji kin that was contaminated with a poisonous mold. It kept sporing with grey mold after just 24 hours. So if the recipe doesn’t seem to be working, it could be because the koji kin is contaminated.
Keywords: koji kin, koji barley, vegan, gluten free, sake, miso, soy free, nut free
Options for Koji Incubation
- I have a Brød & Taylor Bread Proofer & Yogurt Maker, which I use for all my heated ferments. If you plan on doing a lot of fermenting, then I recommend making the investment. I use it for yogurt, cheese, tempeh, everything.
- Using a dehydrator or slow cooker set to 30C is also a great option.
- Alternatively, you can try to grow your koji in the warmest location possible in your house. Try in the oven with the light on, near a radiator or a hot water heater. The only trick is to measure the temperature as you go along because koji mold will start to heat up as it ferments. The right temperature is important because if it’s too cold your mold won’t grow, and if it’s too hot you will kill the spores.
How to Save Koji Mold Spores
Making koji-kin is easy. All you need to do is allow the koji mold to continue growing until it spores, then collect the spores. You will know that the koji-kin has spored when your koji turns from white to greenish-grey. The green colour is mold spores. Once your koji is green, then remove the damp towel, and allow the koji rice to dry out.
When the koji rice has completely dried out, store it in the freezer for future batches of koji. When culturing future batches of koji, you only want to use the green powdered mold, not the rice, so sift the mold off of the rice before using it.