How to Make Soy Sauce at Home (Traditional Brewed Shoyu)

You also need shoyu koji spores, a steamer, an incubator that holds 28–32°C, and a food-grade crock or tub with a lid.

1. 1
   Prepare the soybeans Soak the soybeans for 12–24 hours, then steam them for 1–2 hours or pressure-cook until soft. They should be cooked but not mushy.
2. 2
   Roast the wheat Toast the wheat berries in a dry pan or oven until deep golden and fragrant, then crack them coarsely in a grain mill or blender.
3. 3
   Mix and inoculate While the beans are still warm (about 35°C), toss them with the cracked wheat so it coats them and absorbs surface moisture. Mix in the spores at the supplier’s rate.
4. 4
   Grow the koji Spread 3–5 cm deep in cloth-lined trays and incubate at 28–32°C with high humidity for about 48 hours, breaking up and furrowing it at around 18 and 30 hours to release heat. It is ready when covered in mould and turning yellow-green.

1. 1
   Make the brine Dissolve 250 g of salt per litre of water, which is about 20% by weight. You need roughly 1.2–1.3 litres of brine per litre of koji.
2. 2
   Combine Put the koji in the crock and pour over the brine. Stir well. This mash is the moromi.
3. 3
   Stir Stir daily for the first two weeks, then weekly. Stirring brings oxygen to the yeasts and keeps the surface from moulding. Keep it covered between stirs.
4. 4
   Age Leave it at room temperature for at least 6 months, ideally a year or more. It darkens from tan to deep red-brown and smells increasingly of soy sauce.

1. 1
   Press Ladle the moromi into a strong cloth bag and press it, slowly, with weights or a cheese or fruit press. Collect the dark liquid.
2. 2
   Settle Let the raw soy sauce stand for a few days so oil rises and sediment sinks. Skim the oil and pour the clear sauce off the sediment.
3. 3
   Heat Heat it to about 80°C for 15–20 minutes. This stops the enzymes and microbes and deepens the colour and aroma.
4. 4
   Bottle Bottle while hot, cap and store in a cool place. Keep opened bottles in the fridge.

The pressed cake (shoyu kasu) is still salty and savoury; use it in pickles and marinades.

If a year is too long, homemade miso gives you a little tamari as it ages: the dark liquid that pools on top. Collect it with a spoon or by making a well in the miso, and use it as a rich, mostly soy-based sauce.