** Be sure the entire process, including all utensils, pots, cheese cloth, etc. are as sterile as possible. (Boil utensils for 5 minutes prior to using.) ** Natto yeast needs aerobic fermentation.
Steps: 1. Wash the soybeans and soak for 9 to 12 hours. Use approximately 3 parts water and 1 part soybeans to allow for expansion. You will end up with 8 to 12 cups of beans.
2. Drain the beans from the soaking water. Place beans in a large pot, fill with water and boil for 3-4 hours (until tender but not mushy).
3. Drain the cooked beans and place in a sterilized pot.
4. Wait for the beans to cool down to 40 C. Pour the natto spore over the beans. Stir the beans and mix together carefully using a sterilized spoon.
5. Preheat an oven or a dehydrator to 40 C.
6. Place the covered pot in the oven, dehydrator, or warmer and allow the natto to ferment for 18 hours being sure to keep the temperature steady at 40 C.
7. At the conclusion of the fermentation period, let the natto cool for a couple of hours, then remove the lid and the cloth, replace the lid, and store the containers in the refrigerator at least overnight.
Natto can also be aged in the refrigerator for 3-4 days.
Smaller portions of finished natto can be stored in the freezer and thawed for later use.
