Brewed soy sauce is the traditional, slowly fermented condiment made from soybeans, roasted wheat, salt, and water. Unlike the quick chemical versions, true brewing relies on a months-long fermentation that develops deep umami, complexity, and a balanced salty-sweet profile. This recipe walks you through a small-batch home brew that yields a rich, artisanal sauce you can use in everything from stir-fries to marinades.
Ingredients
- 2 cups (400 g) dried soybeans
- 2 cups (250 g) hard red winter wheat berries
- 1 cup (120 g) all-purpose flour (for the koji)
- 1 tsp (5 g) koji starter (spores of Aspergillus oryzae)
- 1 cup (300 g) sea salt (non-iodized)
- 4 cups (960 ml) filtered water, divided
- Cheesecloth or a clean, breathable cloth
- Large glass or ceramic crock (at least 1 gallon/4 L capacity)
- Weight (e.g., a clean glass jar filled with water)
Instructions
- Prepare the soybeans: Rinse the soybeans and soak them in plenty of water for 12–24 hours until fully hydrated. Drain, then steam or boil them for about 2 hours until they are soft enough to mash easily between your fingers. Drain and let cool to room temperature.
- Prepare the wheat: Toast the wheat berries in a dry skillet over medium heat, stirring frequently, until they are lightly browned and smell nutty (about 10–15 minutes). Let cool, then coarsely grind them in a food processor or blender—you want a gritty texture, not a powder.
- Make the koji: In a large bowl, mix the cooled soybeans with the ground wheat and the flour. Sprinkle the koji starter over the mixture and toss thoroughly to distribute. Spread the mixture evenly in a shallow tray (like a baking sheet) and cover with cheesecloth. Keep it in a warm, humid place (around 85–90°F / 29–32°C) for 48–72 hours, stirring once or twice a day. The mixture should develop a white, fuzzy mold and smell pleasantly earthy—this is the koji.
- Make the brine: Dissolve the salt in 3 cups (720 ml) of filtered water to create a 20% brine. Set aside.
- Combine and ferment: Transfer the koji into the crock. Pour the brine over it and add the remaining 1 cup (240 ml) of water. Stir well to break up any clumps. The mixture should be a thick slurry. Cover the crock with a cloth and secure it with a rubber band. Place the weight on top to keep the solids submerged.
- Ferment: Store the crock in a cool, dark place (around 60–70°F / 15–21°C) for at least 3 months, ideally 6 months. Stir the mixture once a week for the first month, then once a month thereafter. The liquid will gradually darken and develop a rich aroma.
- Press and bottle: After the fermentation period, strain the liquid through a fine-mesh sieve lined with cheesecloth. Press the solids to extract as much liquid as possible. Discard the solids (the okara). Transfer the liquid to a saucepan and bring to a boil, then simmer for 10 minutes to stop fermentation and pasteurize. Skim any foam. Let cool completely.
- Bottle and age: Pour the finished soy sauce into sterilized glass bottles. Seal and refrigerate. The sauce will continue to mellow in flavor over time.
Tips
- Use non-iodized salt: Iodized salt can inhibit fermentation and impart a metallic taste. Sea salt or kosher salt is best.
- Keep it submerged: The solids must stay below the brine to prevent mold growth on the surface. If you see mold, skim it off and make sure the weight is pressing down firmly.
- Be patient: The flavor deepens significantly with time. A 3-month soy sauce will be good, but 6 months or longer yields a more complex, rounder sauce.
- Substitute the koji: If you can’t find koji starter, you can use a commercial koji (like the kind used for miso) and crumble it into the mixture. This will still work, though the flavor may vary slightly.
Serving Suggestions
Use your brewed soy sauce as you would any premium soy sauce: as a dipping sauce for dumplings or sushi, a seasoning for stir-fries, a marinade base for meats, or a finishing splash on soups and rice bowls. Its deep, savory flavor also shines in salad dressings and glazes.
Variations
- Tamari-style: Omit the wheat and use only soybeans (and maybe a bit of rice flour) for a gluten-free version. The flavor will be less sweet and more intensely soy.
- Sweet soy sauce (kecap manis): After pressing, stir in palm sugar or brown sugar to taste (about 1/2 cup / 100 g per cup of sauce) and simmer until dissolved.
- Add aromatics: During the boil, add a few slices of ginger, a clove of garlic, or a star anise for a flavored soy sauce.
Storage and Reheating
Store the brewed soy sauce in a sealed glass bottle in the refrigerator. It will keep for up to 6 months, though the flavor may deepen over time. You can also freeze it in ice cube trays for longer storage—just thaw in the refrigerator before use. If you prefer to keep it at room temperature, it will last about 1 month; always check for off smells or mold.
Frequently Asked Questions
Can I use regular soybeans from the grocery store? Yes, any dried soybeans will work. Just make sure they are not genetically modified if that matters to you, and that they are fresh (not too old).
What if I don’t have a koji starter? You can order koji starter online or from specialty stores. Alternatively, you can use a piece of fresh koji (often sold in Japanese grocery stores) and crumble it. Without koji, fermentation won’t happen properly.
Why does my sauce taste bitter? Bitterness can come from over-toasting the wheat or from fermentation temperatures that are too high. Try toasting the wheat gently and keep the fermenting crock in a cool spot.
Is it safe to eat if I see mold on top? A little surface mold is common and not dangerous if you skim it off and the sauce smells fine. If the mold is fuzzy and covers a large area, or the sauce smells off, discard it.
Can I speed up the process? You can, but the flavor will be less complex. A 1-month ferment will give a mild, slightly sweet sauce, but it won’t have the depth of a longer ferment. Patience is key.
What can I do with the leftover solids (okara)? The okara is nutritious and can be used in veggie burgers, baked goods, or as a protein-rich addition to soups. It has a mild flavor and a texture like fine breadcrumbs.
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