f the soy beans are not yet cooked, pour 3 cups of fresh water into a pot, add beans and bring to a boil. Once the water boils, reduce heat to simmer. Cook until for 1-1 ½ hours or until tender and partially removed from their pods. For faster cooking, use a pressure cooker.
When cooked, add the soybeans to a food processor and blend to a paste. Pour pureed beans into a bowl and combine with flour.
Place the bean-flour mixture on a clean surface and shape into a log. Cut the log into slices about ¼-inch in thickness.
Arrange the soy bean slices on a moist paper towel and cover with another wet paper towel. Cover in cling wrap and put it away in a discreet part of your kitchen or home. Allow to sit for 7 days or until the discs are covered in mold.
Unwrap the discs and arrange them on a baking sheet so they do not touch. Leave them to dry in direct sunlight. Soy bean discs should turn brown when dry. This is the koji.
The next part of learning how to make soy sauce is fermentation. For this, take a pot that you won’t need any time soon. Pour water and salt, stirring to combine. Add the soybean discs and cover. The aim of this step is to dissolve the discs in the salt water, which can take up to 6 months. Stir the mixture daily.
When the soybean slices have completely dissolved, strain the mixture with cheesecloth into bottles for storage. The soy sauce is ready for use. Use soy sauce to flavor meats, seafood, veggies and soups.