Shoyu & Tamari (Soy Sauce)

Why this method

Shoyu (Japanese soy sauce) and tamari are the liquid members of the koji family. Where miso is a packed paste held against air, soy sauce is a submerged mash called moromi: soy-and-wheat koji stirred into a strong salt brine and fermented for months to a year, then pressed. Under brine the koji enzymes liberate amino acids while a community of salt-tolerant yeasts and lactic bacteria (Zygosaccharomyces rouxii, Tetragenococcus halophilus) layer in alcohols, esters, and a gentle acidity. The result is thinner and more aromatic than miso because the prized liquid is separated from the spent solids.

Shoyu uses roughly equal parts soybean and wheat — the wheat gives bright, sweet top notes. Tamari is the near-zero-wheat version, almost all soybean; it ferments longer, runs darker, thicker, and more umami-dense, and is naturally gluten-free.

Parameters

Parameter	Shoyu (koikuchi)	Tamari
Soybean : wheat	~50 : 50	~95-100 : 0-5
Brine salt (% of the brine water)	22-24%	22-24%
Moromi salt (whole mash)	~17-19%	~17-19%
Fermentation temperature	21-27°C / 70-81°F	21-27°C
Fermentation time	6-12 months	8-18 months
Vessel	Wide crock/barrel, stirred	Wide crock/barrel, stirred
Finish	Press, then pasteurize	Press, then pasteurize

Equipment

Wide crock or barrel

Open-topped for daily stirring and oxygen exchange.

Stirring paddle

Moromi is stirred (aerated) regularly, unlike a sealed kraut.

Press + cloth

To separate liquid shoyu from spent solids (kasu).

Scale

Salt is a percentage of the brine water by weight.

Workflow

Make the soy(-wheat) koji

Cook soybeans soft and, for shoyu, mix with roasted, cracked wheat. Inoculate with Aspergillus oryzae and grow koji at 28-32°C for ~48 hours per Growing Koji. For tamari, use all soybean (or a token amount of wheat).

Mix the moromi mash

Dissolve salt into water at 22-24% by weight to make the brine. Stir the koji into the brine to a loose, porridge-like mash. The combined moromi should sit around 17-19% salt overall.

Ferment and stir

Hold at 21-27°C / 70-81°F. Stir daily for the first weeks, then weekly — this introduces oxygen for the yeasts and keeps the surface from going stale. The mash darkens and grows aromatic over months.

Age out

Ferment shoyu 6-12 months, tamari 8-18 months. It is ready when the liquid is deep brown, richly savory, and the raw-soy edge is gone. Cold winters slow it; the long aging is what builds depth.

Press, pasteurize, and bottle

Ladle the moromi into cloth and press slowly to extract the raw shoyu, leaving the spent solids (kasu) behind. Pasteurize the pressed liquid by heating to ~75-80°C to stop enzyme and microbial activity and stabilize flavor and color, then bottle. Refrigerate after opening.