A monk named Kakushin brought a miso method back from Kinzanji in Song China. When that miso is packed, salt draws liquid out of the vegetables and it collects in the bottom of the barrel. Somebody scooped a little of that liquid up and tasted it, and found it remarkable enough to keep. Soy sauce, by this account, begins there.

Yuasa turned out to be suited to the work. The climate here is mild, the water is clean, and fermentation goes well, so brewing became the town's central industry rather than a sideline to something else.

The area around Kitamachi, Kajimachi, Nakamachi, and Hamamachi, roughly four hundred meters by two hundred and eighty, was designated an important preservation district for historic buildings in 2006, the first time that designation had been given to a soy sauce brewing town anywhere in the country.

Kadocho, founded in 1841, still uses the wooden barrels and earthen-walled storehouse it started with. Uncountable microorganisms live in the timber of the barrels and the beams overhead, and the brewing takes a year and a half. The people working there describe their own role modestly: they say they are assisting the bacteria.