Koji is made with koji spores, used to innoculate rice, wheat, barley or soybeans to make a basis from which fermented foods and beverages, such as miso, pickles, shoyu (soy sauce), mirin or saké can be made. It takes 48 hours to make koji and it’s quite involved. It can be purchased ready-made in some areas, but I was interested in the process of growing it, so I ordered koji spores and made my own (one of my journeys into food chemistry). I'm not seriously suggesting you try making this. It is labour-intensive. But I decided to write it up as a node for the ages because people have made koji for centuries. This "recipe" will make enough koji to ferment ten gallons of saké.

You will need the following items to begin making your own koji:


Koji spores can be ordered from G.E.M. Cultures, 30301 Sherwood Road, Fort Bragg, CA 95437 U.S.A. (707) 964-2922. I ordered a 40 gram package of miso koji starter to make saké. A little koji spore goes a long way and it can be tricky to measure. The innoculant ratio is one gram of spore innoculant to eleven pounds of koji substrate. But if you mix the koji spores with rice flour to increase the volume, it’s much easier to measure. The innoculant ratio is one gram of spore-flour innoculant to one pound of koji substrate.

To prepare koji spores for use:

  • Lightly toast two and a half cups of rice flour in a skillet to sterilize it.
  • Cool to room temperature and pour it into a very clean, dry, wide-mouth jar.
  • Tap the koji spore package to move contents to one end.
  • Cut the edge of the package open.
  • With your nose and mouth covered (I used a scarf) pour the koji spores into the jar very slowly, very carefully. Koji spores are very fine and definitely should not be inhaled, so any time you are handling the powder, you should cover your nose and mouth with cloth. Otherwise, you'll be growing mushrooms in your lungs. They are a deep vivid green and pour like smoke. Once the powder is mixed with rice, you won't need to worry about inhaling the spores.
  • Cap the jar and rotate it until the contents are completely mixed and uniform in colour.
  • Label the jar with the date and the type of spores it contains.
  • Measure out the amount of spore mixture needed and replace the cap. Please store the unused portion of the spore mixture in a cool, dry, dark place, such as a refrigerator or air-cooled pantry away from heat sources. Stored in this manner it will maintain full potency for six months or more.

*Note: If you do not own an accurate scale, measuring cups and measuring spoons will suffice. Purchase or grind some slightly course white rice flour which will not pack down and therefore will make measuring more consistent.

To make koji starter (the first twenty-four hours):

  • Wash six cups of a good quality short-grain Japanese white rice, removing as much of the surface starch as is possible. The starch will cause the rice to lump and this is not conducive to growing koji.
  • Soak the rice in twelve cups of distilled or spring water (must be chlorine-free) for six hours.
  • Steam the rice for fifty minutes. You can use the soaking water and just add more water to the pot.
  • While the rice is steaming, sterilize the picnic cooler and the hot water bottles and then, using a thermometer, fill the picnic cooler with water to warm it. The water will need to be 35 degrees centigrade.
  • Just before the rice has finished cooking, fill the hot water bottles with 35 degree centigrade water.
  • Spread a small clean towel on the work surface.
  • Lay a square of unbleached cotton on top of that, large enough to hold the rice.
  • Empty the rice onto the unbleached cotton square, spreading it to an inch in thickness.
  • Check the temperature of the rice. It needs to cool to about 45 degrees centigrade.
  • Cover your nose and mouth with a scarf and sprinkle one teaspoon of the koji/rice flour mixture over the rice.
  • Mix it into the rice well.
  • Spread the rice to a thickness of one inch again.
  • Sprinkle a second teaspoon of the koji/rice flour mixure over it and mix well.
  • Mound the rice in the centre of the cloth to form a ball.
  • Place the thermometer in the ball of rice, top extending so that you will be able to withdraw it to take readings.
  • Wrap the cloth around the ball and then wrap the towel around that.
  • Empty and dry the picnic cooler.
  • Put one of the filled hot water bottles on the bottom of the picnic cooler and then place the wrapped rice ball on top of it.
  • Put the second hot water bottle on top of, or partially covering, the wrapped ball and close the cooler.

You now have a baby koji and you can't leave it unattended. You will need to check its temperature with the thermometer every three hours for the next twenty-four and replace the water in the hot water bottles with 35 degree C. water when the temperature drops. The margin is 25 to 40 degrees centigrade. A caution concerning overheating, also – koji produces its own heat, particularly in the last eight hours.

The second twenty-four hours:

When you unwrap the ball, it will have a sweet, sporey smell. Quite wonderful, actually. The grains should be more or less covered with white powder and flake apart. If this is not the case, you will need to repeat the above, taking care to sterilize utensils etc., as contamination is probably the reason it did not incubate. For the next phase, you will need to:

  • Sterilize two (eight to ten inch) square or rectangular glass dishes baking dishes.
  • Divide the ball of rice evenly in two and spread it in an even layer in each dish.
  • Cut furrows one inch deep and two inches apart. This is done because the spores will be producing their own heat and the furrows prevent the rice from becoming too warm.
  • Cover the bottom of the plastic container with an inch of water.
  • Place the trays in the container, put the lid on it and then cover it with a towel.
  • Check it every four hours for the next twenty-four to make sure that the temperature doesn’t go above 45 degrees centigrade. The margin is now a little wider (25 to 40 degrees is best). If it goes too high or too low, you can regulate it by placing it in another location in your home that is warmer or cooler, or by putting a warmer or cooler hot water bottle underneath the dish inside the container.

After twenty-four hours, have a look. The rice should be covered with a white fuzzy mould, not just on top but throughout, pushing the grains apart. It will look rather like white velvet. You can now use it to make saké, miso, shoyu, pickles, or whatever you wish. It can be refrigerated for about two weeks.

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