Gentle, naturally rich in umami, and perfect for enhancing vegan cooking—Soy Sauce Koji is simple to make and endlessly rewarding.
Making Soy Sauce Koji might sound a little mysterious at first, but don’t worry—it’s really quite simple. This homemade Soy Sauce Koji recipe is full of natural umami, adding gentle sweetness and depth to your dishes without relying on regular soy sauce.
It’s especially perfect for a plant-based kitchen, where seasonings can sometimes feel limited. By using Soy Sauce Koji instead of soy sauce, you’ll enjoy a lighter, lower-sodium option that still brings out incredible flavor.
And the best part? You can use it in so many ways: drizzle it over vegetables, mix it with vegan mayo for a dipping sauce, or stir it into your favorite grains. Even if fermentation feels intimidating, this is a gentle, beginner-friendly process that unfolds naturally with just a little daily care—and a clean spoon.
Jump to:
🥢 What is Soy Sauce Koji?
Soy Sauce Koji is a traditional Japanese seasoning made by combining soy sauce with rice koji, a fermentation starter cultivated from steamed rice. During fermentation, the koji enzymes break down proteins and starches, creating a sauce that is naturally rich in umami, sweetness, and depth of flavor.
Compared to regular soy sauce, Soy Sauce Koji has:
- A mellower, rounder taste that enhances vegetables, grains, and plant-based proteins.
- Lower salt content, making it a lighter yet flavorful alternative.
- A versatility that lets you drizzle it over steamed veggies, stir it into soups, or even mix it with vegan mayo for a simple dipping sauce.
✨ Even if you’ve never worked with koji before, Soy Sauce Koji is one of the easiest fermented seasonings to start with. It requires minimal equipment, just a bit of patience, and the reward is a jar of gentle, naturally complex flavor that brightens your vegan cooking.
🌿 Shio Koji & Onion Koji: Kindred Seasonings
Soy Sauce Koji is part of a family of koji-based vegan seasonings that bring natural umami to your cooking. Among them, Shio Koji and Onion Koji are especially popular and easy to use:
- Shio Koji (Salt Koji):
Made with rice koji, salt, and water, this seasoning adds gentle sweetness and tenderness. It works wonderfully as a marinade or as a natural substitute for salt. If you’d like to learn more about how to make it, see my Homemade Shio Koji Guide. - Onion Koji:
A savory-sweet seasoning made by fermenting onions with koji. It gently enhances vegan soups, stir-fries, or dressings with rich umami. Think of it as a plant-based replacement for bouillon or consommé, perfect for adding depth to Japanese-style curry and other dishes.
✨ What they share in common: all are easy to make at home, gentle on the palate, and excellent for vegan cooking where every layer of flavor counts.
👉 Curious about trying Onion Koji, too? You can find my full Onion Koji Recipe here.
🍘 Ingredients
Soy Sauce:
You can use whichever soy sauce you like best, but here are a few things to keep in mind: Salt content can vary depending on the brand, which will slightly change the taste, fermentation time, and shelf life of your Soy Sauce Koji. Generally, the saltier the soy sauce, the longer it will take to ferment—but it will also keep longer.
To start, we recommend a simple soy sauce made from soybeans, wheat, and salt. Making small batches first is a great way to get comfortable with the process. Once you feel confident, you can experiment with different types of soy sauce to create your very own, personalized Soy Sauce Koji.
Fresh Rice Koji:
This recipe calls for fresh rice koji. If you’re in Japan, you can get it online (for example, on Amazon). If you’re in the U.S., some artisanal miso makers like AEDAN Fermented Foods offer fresh koji. Can’t find fresh koji? Don’t worry! Dried koji works too. Just keep in mind that it absorbs soy sauce differently, so you may need to adjust the amount slightly to get the taste you like.
For exact amounts, please check the printable recipe card👇
🥄 Tools You'll Need
Making Soy Sauce Koji is simple and doesn’t require any fancy equipment. Here’s what you’ll need:
- Clean container or jar – wide-mouthed jars work best so you can mix easily.
- Clean spoon – for stirring the koji daily and scooping out portions without contamination.
- Optional: plastic wrap or a loose lid – to cover the jar while allowing the koji to breathe.
✨ Tip: Keeping your tools extra clean helps prevent unwanted bacteria and ensures a smooth fermentation. Even beginners can make a perfect batch with just these basics!
🥣 Step-by-Step-Guide
If you've already made Shio Koji, soy sauce koji is very easy!
- Combine fresh rice koji and soy sauce
Place your fresh rice koji and soy sauce into a clean jar or container.
🌿 A clean jar and spoon are key to keeping your koji safe and happy.
- Mix gently
Stir thoroughly with a clean spoon until the koji is evenly coated. Cover the jar lightly with the lid slightly open or with plastic wrap—this lets the koji “breathe” while fermenting.
🌿 Leave it at room temperature, ideally somewhere around 20–25°C (68–77°F)
- Let it rest
Place the jar at room temperature, out of direct sunlight.
🌿 In summer, it usually takes about a week to ferment; in winter, closer to two weeks.
- Check the koji absorption
After the first day, you’ll see the koji starting to absorb the soy sauce. The top may look dry while the bottom is moist—this is normal.
- Pour soy sauce over the dry spots
Gently pour just enough soy sauce to cover the dry parts of the koji.
🌿 For the first two days, if the surface looks dry, add a little more soy sauce—once or twice is usually enough.
- Mix and settle
Stir gently with a clean spoon so the koji absorbs the soy sauce evenly. The mixture should now be just covered with soy sauce.
- Stir daily
Using a clean spoon, stir roughly once a day. This ensures even fermentation.
🌿 The photo shows the soy sauce koji on the third day of fermentation.
- Check readiness
Around day 5-7 (or longer in winter), the koji will have softened and absorbed the soy sauce completely. It should be easy to crush gently with your fingers.
✨ Small daily steps and a clean spoon are all you need to create a naturally umami-rich, gentle Soy Sauce Koji that elevates any vegan dish.
📖 Variations & Recipes
Soy Sauce Koji is wonderfully versatile, bringing gentle umami and natural sweetness to vegan dishes. Here are some simple ways to enjoy it:
- Drizzle over vegetables
Steam or roast your favorite veggies, then lightly drizzle Soy Sauce Koji over them. It adds depth without overpowering their natural flavors. - Mix with vegan mayo for a dip
Combine Soy Sauce Koji with vegan mayonnaise for an easy, flavorful dip. This goes perfectly with Vegan Avocado Sushi Rolls, roasted potatoes or fries, and other favorite snacks. The possibilities are endless! - For wasabi lovers: Japanese yam with Soy Sauce Koji
Thinly slice Japanese yam and gently coat it with Soy Sauce Koji and a hint of wasabi. This creates a crunchy, and umami-rich bite that’s perfect as a side dish. If you spot Japanese yams at your supermarket, this easy preparation is definitely worth trying! - Stir into grains, noodles, or stir-fries
Season rice, noodles, or vegetable stir-fries like Vegan Beef & Green Pepper Stir Fry, or Vegan Steamed Rice with Bamboo Shoots, even Vegan Takoyaki. Soy Sauce Koji elevates these dishes with natural richness.
✨ Even if you’ve never used fermented seasonings before, these ideas make it easy to experiment. Start small, have fun, and discover how Soy Sauce Koji can brighten your vegan cooking.
More recipes are HERE!
🫙 Storage
Once your Soy Sauce Koji is ready, simply keep it in the same clean jar with a tight lid and store it in the refrigerator. It will stay good for about 3 months, depending on the salt content and how carefully you handle it.
A few gentle reminders:
- Always use a clean spoon when scooping out your koji to prevent contamination.
- Check the aroma and taste before use—if it smells or tastes off, discard it.
- The koji may continue to mature slowly in the fridge, so feel free to stir it occasionally.
Refrigeration slows down fermentation, so your Soy Sauce Koji will stay flavorful and safe to use over time.
💭 Questions (FAQ)
Even if this is your first time working with koji, don’t worry! Here are some common questions and tips:
A: This is normal! It means the koji is fermenting. Simply stir it gently with a clean spoon, and it will mix back together.
A: Fermentation depends on room temperature. In summer, it usually takes about a week; in winter, around two weeks. The koji is ready when you can crush it gently between your fingers.
A: Don’t worry at all! Soy Sauce Koji is quite forgiving. Even if you forget to stir for a day—or a few days—it will still turn out fine. Just resume gentle daily stirring when you remember. (Salt Koji is a bit more sensitive, but Soy Sauce Koji is easygoing!)
A: Yes! Start with a small batch and taste as it ferments. You can add a bit more soy sauce if needed.
✨ Tip: Using a clean spoon each time you stir not only keeps your koji safe but also makes the process stress-free and beginner-friendly.
If you like this recipe or have already made it, we'd love to hear your thoughts in the COMMENTS 🐒. Also feel free to ask any questions or leave any requests!
👨🏻🍳 Recipes with Soy Sauce Koji
✌️ Latest Vegan Recipes
Home Made Soy Sauce Koji
Equipment
- Glass container or Jar
- Clean spoon
Ingredients
- 150 ml Soy Sauce (Choose a simple soy sauce made from soybeans, wheat, and salt. Add more if needed as fermentation progresses.)
- 150 g Fresh Rice Koji (If you can't find fresh koji, dried rice koji can be used; adjust soy sauce accordingly.)
Instructions
- Combine fresh rice koji and soy sauce: Put the fresh rice koji and soy sauce in a clean container.150 ml Soy Sauce150 g Fresh Rice Koji
- Mix gently: Mix thoroughly with a clean spoon. Cover lightly, leaving a small gap for the koji to breathe.
- Check the koji absorption: The next morning, the koji will have absorbed the soy sauce and the upper half may be dry. Add just enough soy sauce to cover the koji and mix gently.* For the first two days, if the surface looks dry, add a little more soy sauce—once or twice is usually enough.
- Stir daily: Stir roughly once a day with a clean spoon. In summer, it will be ready in about 1 week; in winter, about 2 weeks. You'll know it's ready when the koji can be easily crushed with your fingers.
- Check readiness: When fermentation is complete, the soy sauce flavor will be softened and the koji will have a sweet, mellow depth.
- Store: Close the lid tightly and store in the refrigerator. Use as a versatile seasoning in vegetables, dips, soups, or grains.
Notes
- Even if you forget to stir for a day, Soy Sauce Koji is forgiving—just resume gentle daily stirring when you remember.
- For more about Shio Koji and Onion Koji, see my related guides.
We'd absolutely love to see your photos of the dishes you've made with our recipes! Share them on Instagram with the hashtag #vegin_vegan_vegun or just tag us @veginveganvegun 🙏
Mika says
It was easy and tasted so good!