Homemade Shoyu Koji (Soy Sauce Koji)
An effortless, umami-packed Japanese fermented seasoning made with rice koji and soy sauce. This recipe is perfectly scaled to fit a standard 16 oz glass jar and features optional steps for a smooth, pourable paste ideal for dressings, marinades, and dipping sauces.
Servings: 1 jar
Calories: 23kcal
Ingredients
- 160 g Dried Rice Koji
- 400 ml Japanese Soy Sauce (Shoyu) (Honjozo/naturally brewed)
- 30 ml Water (optional for a less pasty consistency)
Instructions
Preparation & Mixing
- Sanitize Equipment: Thoroughly clean and sanitize your mixing bowl, a 16 oz glass jar, and mixing spoons with boiling water or food-grade alcohol. Let them dry completely.
- Combine Ingredients: Weigh 160g of rice koji into the sanitized mixing bowl. Pour the soy sauce over the koji and stir well until all grains are evenly coated and submerged.
- Transfer to Jar: Pour the mixture from the bowl into your clean 16 oz jar. Secure the lid.
Fermentation (Choose One Method)
- Method A (Room Temperature): Store the jar in a cool, dark, and clean place for 1 to 2 weeks (up to 4 weeks in winter). No daily stirring required.
- Method B (Yogurt Maker): Set your yogurt maker to 60°C (140°F) for 6 hours to rapidly develop sweetness and umami.
- Method C (Oven/Proofer): Place the jar in an oven with a proofing or fermentation setting at 55°C–60°C (130°F–140°F) for 6 to 8 hours. Stir a few times during the process to assist fermentation.
Finishing & Adjustments
- Hydration Check (Next Day): If using dried koji, check the jar the next day. If the top layer looks dry, add a small splash of extra soy sauce until the grains are completely submerged.
- Thin the Texture (Optional): After 1 week of room temperature fermentation (or immediately after a machine cycle), stir in 1/4 cup of water if you prefer a smoother, pourable texture over a thick paste.
- Blend (Optional): Once the koji grains are fully softened, use a hand blender to blitz the mixture into a completely smooth, uniform paste. Store in the refrigerator for up to 3 months.
Notes
- Soy Sauce Selection: Always use traditional, naturally brewed soy sauce (Honjozo). Avoid low-sodium varieties because the reduced salinity can compromise shelf-life and allow harmful bacteria to form during room temperature fermentation.
- Freezer Friendly: If you won't finish the batch within 3 months, freeze it in a silicone mold or freezer bag for up to 6 months. Due to the high salinity, it won't freeze rock-solid, meaning you can easily scoop it straight out of the freezer!
- Looking for Salt Koji? If you love this recipe, try my signature Homemade Shio Koji Recipe to round out your fermented pantry staples!
Nutrition
Serving: 15g | Calories: 23kcal | Carbohydrates: 1.4g | Protein: 1.2g | Sodium: 516mg | Sugar: 1.8g