Homemade Koji Rice

Homemade koji rice right before it starts to spore

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4.9 from 8 reviews

Koji rice (and koji barley) is used to make miso, sake, amasake, rice vinegar, soy sauce, and mirin. Here’s how to use koji kin to make koji rice and koji barley. See the sections above for information on incubation options and how to save your own koji kin.


Units Scale
  • 2 cups rice (white or polished brown)
  • 1/4 tsp koji-kin culture (see notes)


  1. Rinse the rice until the water runs clear (to remove all the starch).
  2. Soak the rice in water for 8-12 hours.
  3. Steam (not boil) the rice until it has softened. See notes below for my setup.
  4. Cool the rice to room temperature.
  5. Thoroughly mix the koji-kin culture into the rice.
  6. Spread the rice out in a baking dish. Cover with a damp tea towel (to keep it moist but not wet) and maintain it at 90 F (30 C) for 48 hours. See the section above for incubation options.
  7. Stir the rice every 12 hours to break up the clumps and evenly distribute moisture. After 48 hours, white mold fibers should have started to develop. Stop incubating at this point or the mold will spore.
  8. Store koji rice in the freezer until you are ready to use it to make miso, sake, or other koji ferments.
  9. See the section above for details on how to save koji-kin mold spores for future batches of koji rice.


  • Since this is a mold ferment it’s important to keep everything clean and sanitized.
  • For koji barley, use pearled barley instead of rice and follow the same procedure. Note: I haven’t personally tried this as I’m gluten-free.
  • For steaming, I recommend using a vegetable steamer or colander lined with a tea towel.  Just boil the tea towel 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.