Making soy sauce at home is a rewarding project that yields a rich, complex condiment far fresher than most store-bought bottles. This recipe uses a simplified fermentation method with koji (the same mold used for miso) to create a deeply savory, umami-packed sauce in about two weeks. While it won’t replicate the exact flavor of a 2-year-aged artisanal soy sauce, it produces a delicious, versatile sauce that is perfect for dipping, marinades, and stir-fries.
Ingredients
- 2 cups (300 g) dried soybeans
- 1 cup (120 g) all-purpose flour (or whole wheat flour for a deeper flavor)
- 2 tbsp (15 g) koji starter (spores) or 1 cup (200 g) rice koji (see Tips)
- 3 cups (700 ml) filtered water
- 1/2 cup (120 ml) sea salt (non-iodized)
- 1/4 cup (60 ml) sake or dry sherry (optional, for flavor)
Instructions
- Rinse the soybeans and soak them in plenty of water for 12 hours, or overnight. Drain and place in a large pot. Cover with fresh water and bring to a boil, then reduce to a simmer. Cook until the beans are very soft and can be easily mashed with a fork, about 3 hours. Drain and let cool to room temperature.
- Once the beans are cool, mash them with a potato masher or your hands until they form a coarse paste. Mix in the flour and the koji starter (or rice koji) until well combined. The mixture should be crumbly but hold together when pressed.
- Shape the mixture into a firm ball or patty, about 2 inches thick. Place it on a clean, dry surface (like a bamboo mat or a wire rack) and cover with a clean cloth. Let it ferment in a cool, dark place (ideally 70°F / 21°C) for 48 hours. You should see a white mold bloom on the surface—this is the koji. It is safe and expected.
- After 48 hours, break the fermented cake into small chunks and place them in a large glass or ceramic jar. Stir in the salt and the filtered water. The mixture will be very salty and thick. Cover the jar with a cloth or a loose lid to allow air circulation but keep out dust.
- Place the jar in a cool, dark place (around 60–70°F / 15–21°C) and let it ferment for 10 to 14 days. Stir the mixture once every day with a clean, dry spoon. You will notice a dark liquid forming—this is the soy sauce.
- After 10–14 days, the liquid should be dark and fragrant. Strain the mixture through a fine-mesh strainer lined with cheesecloth. Press the solids to extract as much liquid as possible. Discard the solids (the okara).
- Pour the liquid into a saucepan and bring to a boil over medium heat. Reduce to a simmer and cook for 5 minutes. This stops the fermentation and sterilizes the sauce. If using, stir in the sake or sherry. Let cool completely.
- Bottle the finished soy sauce in a clean glass jar or bottle. It will keep for several months in the refrigerator.
Tips
- Koji: Koji starter (spores) is available online or at Asian grocery stores. If using rice koji (which is already inoculated), use 1 cup (200 g) and skip the 48-hour fermentation step, as the koji is already active. Simply mix the rice koji into the mashed beans and proceed to the brining step.
- Salt: Use non-iodized salt (like sea salt or kosher salt) to avoid a bitter taste. The salt is essential for preventing unwanted bacteria growth during fermentation.
- Flavor: For a sweeter, more mellow sauce, add 1 tablespoon of brown sugar or molasses to the simmering step. For a spicier version, add a few slices of fresh ginger or a dried chili to the jar during fermentation.
- Common Mistake: Do not skip the daily stirring. This prevents mold from forming on the surface and ensures even fermentation. If you see a small amount of white mold, skim it off—it’s harmless, but black or green mold means the batch is spoiled and should be discarded.
Serving Suggestions
Use this homemade soy sauce as a dipping sauce for dumplings, sushi, or spring rolls. It works beautifully as a marinade for chicken, beef, or tofu, and can be used in stir-fries, noodle dishes, or as a seasoning for soups and stews. Drizzle it over steamed vegetables or rice for a quick, savory boost.
Variations
- Tamari-style: Replace the soybeans with an equal amount of chickpeas or black beans for a gluten-free, slightly different-flavored sauce.
- Sweet soy sauce (kecap manis): After simmering, stir in 1/2 cup (100 g) of brown sugar and 1/4 cup (60 ml) of water until dissolved. This creates a thick, sweet sauce perfect for Indonesian-style dishes.
- Garlic soy sauce: Add 3-4 crushed garlic cloves to the jar during the fermentation step for a garlicky, aromatic sauce.
Storage and Reheating
Store the finished soy sauce in a sealed glass jar or bottle in the refrigerator. It will keep for up to 6 months, though the flavor may mellow over time. The sauce does not need reheating—use it cold or at room temperature. If you prefer it warm, heat gently in a saucepan over low heat, but do not boil, as this can alter the flavor.
Frequently Asked Questions
Can I use this soy sauce immediately after bottling? Yes, the sauce is ready to use as soon as it is bottled and cooled. However, the flavor will continue to develop and deepen over the first week in the refrigerator.
Why is my sauce cloudy? Cloudiness is normal and is caused by tiny particles of the fermented solids. It will not affect the flavor. You can filter it through a coffee filter for a clearer sauce.
How long can I store it? In the refrigerator, it will keep for 4-6 months. Always use a clean, dry spoon when taking out sauce to avoid introducing bacteria. If you see any mold or off-odor, discard it.
Can I make soy sauce without koji? No, koji is essential for breaking down the proteins and starches into amino acids and sugars, which create the characteristic umami flavor. Without it, you will end up with a salty bean paste, not soy sauce.
Why does my sauce taste too salty? The salt is necessary for preserving the sauce and controlling fermentation. If it tastes too salty for your palate, you can dilute it with a little water when using, but do not reduce the salt in the recipe, as it may spoil.
Is this safe for people with gluten allergies? Traditional soy sauce is made with wheat, but this recipe uses flour. If you need a gluten-free version, use a gluten-free flour blend or omit the flour entirely and increase the koji to 1.5 cups (300 g). The texture will be slightly thinner, but the flavor will be similar.
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