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Making miso is a long process with several stages. First, koji is grown; then the koji is mixed with cooked grain, salt, and water, packed tightly, and left to mature.

Koji is a cultivated mold, Aspergillus oryzae. Its enzymes help break down proteins and starches during miso fermentation. Like sourdough starter, living koji needs to be grown, cared for, and used while active.

Ingredients:

For the koji

  • Dried koji spores, purchased online or received from someone who grows koji
  • 2 lb 3 oz organic pearl barley (1 kg)

For the miso

  • Fresh koji
  • Cooked wheat berries
  • Water
  • Salt

Instructions:

Growing the koji

  1. Soak the pearl barley in water for 24 hours.
  2. Rinse the barley, transfer it to cheesecloth or a thin cotton cloth, and steam it in a steamer basket for about 1 hour.
  3. Spread the steamed barley on a surface and let it cool to about 86 F (30 C). It should feel warm, not hot.
  4. Sift the dried koji spores evenly over the warm barley, as if dusting with powdered sugar.
  5. Keep the inoculated barley warm and humid, about 86 F (30 C) or slightly warmer, for 48 to 72 hours.
  6. During the first day, make sure the koji stays warm, around 86 to 95 F (30 to 35 C).
  7. During the second day, the koji begins producing heat on its own. Break it up gently from time to time so heat does not build up in pockets with less airflow.
  8. After about 48 hours, the fresh koji is ready to use.

Ways to keep koji warm and humid

  1. In very hot weather, wrap the inoculated barley in cloth, place the bundle in a paper bag to preserve humidity, and keep it in a warm room without air conditioning.
  2. Make a simple home incubator by wrapping the koji in cloth, placing it in a tray inside a cooler, and adding a hot water bottle. Refresh the hot water as needed.
  3. Place the koji in a shallow tray, wrapped in cloth, in an oven set to 86 F (30 C), without convection so it does not dry out. Put a jar of water near the tray to help maintain humidity.

Fresh koji can be frozen and thawed when needed. If using it within a week, keep it in a container in the refrigerator. To save koji for the next batch, dry some koji-covered barley at 86 F (30 C) in a dehydrator or oven, then store it in a jar.

Making the miso

  1. Grind fresh koji and cooked wheat into a paste, using a ratio of 1 part koji to 2 parts wheat.
  2. Weigh the paste and add water equal to half the paste weight.
  3. Add salt equal to 13% of the total weight of the paste and water: 4.6 oz salt per 2 lb 3 oz mixture (130 g per 1 kg).
  4. Mix well.
  5. Transfer the mixture to a glass or ceramic vessel. Press it down firmly so no air pockets remain.
  6. Sprinkle a thin layer of salt over the packed mixture, place a piece of cheesecloth or thin cotton cloth on top, and add a weight to press the miso down.
  7. Cover the vessel with cloth secured with a rubber band, or with a loose lid.
  8. Let the miso rest. Check and taste it after about 3 months. If needed, replace or rinse the cloth, cover the miso again, and let it continue aging.
  9. The longer miso ages, the sharper and deeper its flavor becomes. It is usually ready after 1 to 2 years.

Soy-sauce-style liquid

To make a sauce similar in flavor to soy sauce, add more water at the mixing stage. This is a matter of experimentation. During the 1 to 2 years of fermentation, solids settle and liquid collects above them. At the end of fermentation, strain the mixture through cloth: the solids are the miso, and the liquid is the sauce.

Advanced fermentation note: Koji and long-aged miso require careful temperature, humidity, salt, and cleanliness. Grow only known food-grade koji, protect it from insects and debris, and do not use or taste anything with an unpleasant smell, unusual color, or mold growth that does not match healthy koji or miso.