This is a top view of the cedar barrels that were observed on the first floor.

To begin soy sauce brewing, first, make Koji (rice malt) by blending equal amount of steamed soybeans and toasted wheat, then add seed malt.  Second, the Koji is placed in a tank with brine to create Moromi, and it is rested for approximately 1 to 2 years with repeated stirring.

Osmophilic (enzyme), yeast, lactic acid bacteria etc. help break down ingredients and further maturation creates the distinctive color, flavor, and fragrance of soy sauce. The original key ingredients are domestic round soybeans, domestic flour, and bittern salt from Gotonada. Moromi (unrefined soy sauce) creates Koji (rice malt) with soy beans and flour, and it is rested with brine through fermentation and maturation. Moromi (main fermenting mash) contains millions of live yeast and lactic acid bacteria, thus workers occasionally need to stir the mixture using long sticks to let those microorganisms breathe inside the barrels.

Typically, soybeans are steamed; however, the traditional method is characterized by cooking soybeans slowly and using brine to ferment. By using this method, nutrients of soybeans including Isoflavone, Lecithin, and Saponin are fully extracted. The preparation of the soy sauce typically starts in winter and follows several steps as follows: letting the mixture mature in the natural cedar barrels for over a year, squeezing Moromi, transferring the raw soy sauce to large wooden vats, and precipitating impurities out of raw soy sauce. At the end, the liquid emerges on the top layer becomes soy sauce.