House Shoyu

House shoyu is deep brown, brightly savory, and aromatic — the liquid member of the koji family. Unlike packed miso, soy sauce is a submerged mash (moromi): soy-and-wheat koji stirred into a strong salt brine, fermented for months while halophilic yeasts and lactic bacteria layer in alcohols and esters, then pressed and pasteurized. For wheat-free tamari, use nearly all soybean and age longer. This recipe follows the Shoyu & Tamari method.

Ingredients

Work by weight. Brine salt is a percentage of the brine water; the finished moromi lands around 17-19% salt overall. A “Jar” is a quart/litre wide crock or jar; a “Crock” is a 2 L open crock or barrel for daily stirring.

Component	1 Jar (~1.5 L moromi)	1 Crock (~3 L moromi)
Cooked soybeans	250 g	500 g
Roasted, cracked wheat (for shoyu)	250 g	500 g
Tane-koji spores (A. oryzae)	~0.5 g	~1 g
Water (for brine)	750 g	1,500 g
Salt (23% of brine water)	173 g	345 g

Note

Brine salt is 22-24% of the brine water (23% shown: 750 g water × 0.23 = ~173 g salt). Once the soy-wheat koji is folded in, the whole moromi sits around 17-19% salt — the high figure that makes this self-protecting. Use the brine-salinity calculator to size the salt for any water volume. For tamari, use ~95-100% soybean and a token amount of wheat.

Yield

About 600-700 ml raw shoyu per Jar / ~1.3 L per Crock after pressing, plus the savory spent solids (kasu). Pasteurized and bottled, it keeps well; refrigerate after opening.

Calculated values

• Brine salt %: 22-24% of the brine water (23% default).
• Moromi salt %: ~17-19% of the whole mash — this is the safety hurdle.
• Soybean : wheat: ~50 : 50 for shoyu; ~95-100 : 0-5 for tamari.
• Target finished pH: ~4.5-4.8 — moromi develops a gentle acidity, but salt, not acid, is the barrier.
• Fermentation temperature: 21-27 °C / 70-81 °F.
• Fermentation time: 6-12 months (shoyu); 8-18 months (tamari).

Info

Soy sauce is not an acidic ferment in the safety sense — its stability rests on the 17-19% salt in the moromi, which suppresses everything except the intended halophilic yeasts (Zygosaccharomyces rouxii) and bacteria (Tetragenococcus halophilus). Never dilute the brine to speed fermentation; at lower salt the mash is no longer self-protecting.

Readiness window

	Detail
Early	Months 1-2: pale, raw-soy aroma, daily stirring
Maturing	Months 3-8: darkening, aromatic, weekly stirring
Done	6-12 months (shoyu); longer for tamari
Arrest	Press, then pasteurize to ~75-80 °C to stop activity

Done when: the liquid is deep brown, richly savory, and the raw-soy edge is gone. Cold winters slow it; the long aging builds the depth. Because salt and pasteurization (not refrigeration) arrest this ferment, judge by color and aroma over months, then press.

Method

Make the soy-wheat koji

Cook soybeans soft. For shoyu, mix with roasted, cracked wheat (~50:50). Inoculate with Aspergillus oryzae and grow koji at 28-32 °C for ~48 hours per Rice Koji / Growing Koji. For tamari, use all (or nearly all) soybean.

Mix the moromi mash

Dissolve salt into the water at 22-24% by weight to make the brine. Stir the soy-wheat 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 few weeks, then weekly — this introduces oxygen for the yeasts and keeps the surface fresh. 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.

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.

Tip

The pressed solids (kasu) are not waste — they are intensely savory and salty. Use them as a marinade base or pickling bed, the same way sake kasu is used.

Caution

Soy sauce’s safety rests entirely on the 17-19% salt in the moromi — it is not protected by acidity. Never reduce the brine strength to make a “low-sodium” home version: at lower salt the mash is no longer self-protecting and can spoil dangerously. The finished sauce sits above the botulism line; keep it salty, ferment it long, pasteurize it, and refrigerate after opening. Do not can a reduced-salt soy sauce; refer formulation questions to NCHFP.

Variations / mix-ins

• Tamari (gluten-free): ~95-100% soybean, little or no wheat — darker, thicker, more umami-dense, aged longer.
• Barrel vs jar: any wide non-reactive vessel works; the open top is for daily stirring and oxygen exchange.
• Solar aging: traditional makers let summer warmth drive color and depth, slowing through winter.

See also

• Shoyu & Tamari — the full moromi method and press detail
• Rice Koji and Growing Koji — soy-koji is the starting point
• Making Miso — the paste cousin; tamari also pools atop miso
• Brine Chemistry and Salt Percentage
• Brine-salinity calculator
• Safety and Botulism