Koji is an invaluable ingredient to Japanese and Asian food culture.
It is a principal ingredient in miso (bean paste), shoyu (soy sauce) and sake (Japanese liquor).
In essence, koji is rice incubated with koji-kin, or koji fungus: spores from the mold "asperlligus oryzae". Once the rice is fully incubated with koji-kin, it can then be mixed with beans, water or rice to make these delicious foods and drinks.
The large variety and amount of enzymes produced by the mold plays a significant role in the transformation process of rice into saké or amazake, as well as soybeans into miso or Shoyu. The enzymes are also used in different culinary creations, such as bettarazuke (a fermented pickle using daikon radish), or shio-koji, a salted condiment used to tenderize meat and fish.
The active enzymes of Koji keep working after consumption, helping digestive functions in our body.
Here is a brief introduction on how we make home-made koji:
First, we rested white rice in water for a night. The following day, the rice was poured into wooden containers and prepared to be steamed.
We made a fire in the oven to boil a large pot with water in order to stack the rice on top of it.
The rice was steamed for around an hour.
The rice is mixed and cooled down to 46 degrees Celcius before mixing in the koji-kin. Any hotter than 46 degrees and the fungus will not be able to incubate, eventually dying off
Once the rice is cooled, a few grains of rice fully incubated with koji-kin (bought separately) are mixed into the fresh rice
The koji-kin is carefully mixed into the rice by hand.
The rice and koji-kin mixture are poured into paper bags to be rested indoors
Since heat comes with the process of fermentation and incubation, the rice and koji-kin mixture must be constantly heated at 30 degrees for 18 to 24 hours depends on the temperature of the atmosphere (durng winter time, the mixture needs to be heated for 24 hours). In Japan, a kotatsu (炬燵) can be used to maintain the correct temperature. Others devices can also do the work such as an oven or a heater
After the rice becomes white, dry, and covered in mold, the koji is ready
Photos by EK/ET and descriptions by LKO/ET.