Steam soy beans, the base ingredient
Roast and crush wheat. Add it with seed malt to the steamed soy beans. Stir together.
Stirred ingredients are stored in the kojimuro (koji room).
Make koji malt by fermenting the ingredients under controlled temperature for 48 hours.
Make moromi mash by adding salt water and koji malt into cedar tubs.
Stir to facilitate natural fermentation over a 2 to 3 year period.
After sufficient aging, wrap moromi mash in cloth to strain out the liquid.
Heat the strained liquid to pasteurize and to adjust the flavor and color.