Koji – Rice (Fermented Rice)

Makes around 1.2kg of Koji (*weight depends on the dryness)


  • 5 cup/1kg      polished (white) rice, medium or short grain
  • ¾~1tsp          Koji starter (spore)
  • *1 cup = 250ml


  • 1        4~6 quart stock pot with lid
  • 1        large sieve or colander with fine mesh (or 2 or more small ones)
  • 1        set of steaming utensils that fit in the stock pot (e.g. daisy wheel steamer and stand)
  • 1        mixing spoon
  • 1        measuring spoon
  • 1        thermometer
  • 1       10”x14”x2 ½” container (alternatively 2 small, Tupperware works)
  • 3~5    tight weave tea towels or sheets of cheese cloth
  • 1        large cooler box
  • 1~2    large 3~4” deep Tupperware with lid
  • Rubbing alcohol
The night before:

Wash and soak rice (overnight ~ 24hr).

Day 1:

Drain rice well (around 1hr), spread thinly or turn it upside down while draining to dry evenly.

669 steam rice
Wrap with a damp tea towel or cheese cloth.

671 steam rice

Steam rice (around 1hr).

Steamed rice – much drier than ordinary cooked rice.

Sterilize the work space and all utensils with rubbing alcohol (dry completely before use).

Stir cooked rice quickly to evaporate extra moisture, break chunks and separate grains as much as possible.

711 cool rice

Mix Koji starter thoroughly when rice is 45˚C/114˚F, rub well with hands.

688 day 2 break koji

Wrap with a damp tea towel, place thermometer.

694 wrap koji

Set in the cooler box with covered container filled with warm water (keep Koji internal temperature around 30˚C/85˚F).

702 koji in cooler with lid

Until bed time check temperature every 2~4 hours to maintain 30˚C/85˚F +/-.

Day 2:

After 20~24hr fermentation, spread Koji thinner (~1”), cover with a new damp tea towel and put it back to cooler box, maintain temperature and moisture.

Until bed time check temperature every 3~4 hours to maintain 30˚C/85˚F +/-.

Day 3:

After 46~48hr fermentation, finish fermentation.

Break into pieces, spread over a large surface (like a cookie sheet) and dry it for a half day/over night.

Use right away or refrigerate (up to a month)/freeze (up to 6 months).


Sterilize utensils and work space thoroughly. Do not consume it if anything is suspicious (color, smell, texture, etc)

Try Miso and Amazake with homemade koji.

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