Soybeans are harvested in Autumn and Miso is made in mid-Winter (Jan-Feb in Japan), and then left to ferment for at least nine months before eating. Miso is made from three ingredients: malted rice or barley, soybeans and salt. The key to making good miso is using a good quality rice malt (koji), getting absolutely all the air out when putting the miso into the container, and keeping it in a really cool spot (under-house storage, or refrigerator) to prevent mold.
Koji starter (malted rice) is usually made by fermenting cooked rice for 48 hours with aspergillus oryzae, a fungus, also called koji-kabi, literally koji-mold. But this is too hard, so I buy nama-koji online in Japan from Tomizawa-shoten. Nama-koji is rice that has already been fermented with the koji mold, so it is ready to use.
Recipe (makes approx. 4-5kg miso)
1 kg soybeans
1kg fresh rice malt (nama-koji)
Also, reserve 100 – 200 ml of the water used to cook soybeans (‘nijiru)
1. Soak soybeans in 3 times the volume of water, for 17 hours.
2. Cook soybeans for 20 minutes in a pressure cooker, or boil for 2 hours or until soft.
3. Drain, but reserve the liquid (called ‘nijiru’).
4. Crush soybeans, with sterilized hands, potato masher, or food processor.