Gentle, savory-sweet, and full of natural umami—Onion Koji is a simple, plant-based alternative to consommé cubes and veggie bouillon.
Discover how this simple, fermented seasoning adds depth and richness to any vegan, vegetarian and plant-based cooking.
▼ Onion Koji Recipe Ideas
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🌿 What is Onion Koji?
Onion Koji (玉ねぎ麹) is a Japanese umami seasoning made with just onions, rice koji, and salt—what I call a vegan consommé. It’s a foundation for creating flavorful plant-based dishes without relying on store-bought bouillon.
Why it matters
For vegan and vegetarian cooking, seasonings can sometimes feel limited. Onion Koji naturally steps in as an alternative to consommé cubes, veggie bouillon, or even prepared broth—without additives or overpowering saltiness.
Simple ingredients, big flavor
You only need three things: onions, fresh rice koji, and salt. With just these, you’ll create a seasoning that layers flavor into Japanese-style curry, pasta sauces, or even a simple miso soup.
A little jar of magic
Once made, Onion Koji becomes your go-to flavor enhancer. A spoonful stirred into hot dishes instantly brings depth, richness, and a gentle sweetness that feels almost like slow-cooked stock.
Endless possibilities
And the best part? Together with Shio Koji and Soy Sauce Koji, Onion Koji gives you endless possibilities to season vegan food with depth and variety.
🧅 Ingredients
Just three simple, natural ingredients come together to make Onion Koji:
- Onions – Choose fresh, sweet onions for the best natural sweetness.
- Natural Salt – Enhances the flavors and helps preserve the koji naturally.
- Fresh Rice Koji – The key ingredient that transforms simple onions into rich, savory umami. You’ll need fresh rice koji for this recipe. In Japan, it’s available online (for example, Amazon), and in the U.S., some artisanal miso makers like AEDAN Fermented Foods offer fresh koji. If fresh koji isn’t available, dried koji works too—just adjust accordingly, as it absorbs moisture differently.
For exact amounts, please check the printable recipe card👇
🥄 Tools
- Grater, Food processor or Hand blender
- Bowl
- Spatula
- Spoon
- Glass food storage container
🥣 Step-by-Step Guide
- Prepare the ingredients
- Grate the onion and place it in a bowl with salt and fresh rice koji.
- Mix well
- Using a spatula, mix the ingredients thoroughly.
- The mixture should be uniform, with the salt and koji evenly coating the grated onion.
- Transfer to a storage jar
- Put the mixture into a clean glass jar or food storage container.
- Close the lid lightly and keep it out of direct sunlight. In summer, it will mature in about a week; in winter, around two weeks.
- If the color starts to change, stir gently with a clean spoon each time.
🌿 A clean jar and spoon are key to keeping your koji safe and happy.
- Maturing
- The Onion Koji is ready when it turns a beautiful pink-beige or beige and can be easily crushed with a finger.
- At this point, close the lid tightly and store it in the refrigerator.
👀 Tips:
If the color changes while you’re making it, don’t worry—this is just the koji maturing.
You can leave it as is, or give it a gentle stir from time to time to keep the color and flavor more even.
If you notice any unusual smells or mold, it’s best to start over with a fresh batch.
🫙 Storage
Store your Onion Koji in a clean, airtight container in the refrigerator.
It’s best used within about three months, while its gentle sweetness and umami are at their peak.
🧑🏼🍳 Note When Using
Whenever you use your Vegan Consommé Onion Koji, give it a gentle stir from the bottom to make sure the flavors are evenly distributed.
The salt tends to settle at the bottom, so mixing well each time is key.
And always use a clean spoon for serving to keep your koji fresh and flavorful.
💭 Questions
Shio Koji is a basic seasoning made with just rice koji and salt. Onion Koji adds grated onion, giving it natural sweetness and deeper umami. Its mild onion flavor makes it versatile for both Japanese and Western-style dishes.
Unlike Shio Koji, daily stirring isn’t necessary. You can give it a gentle mix if you want to even out the color or prevent salt from settling at the bottom.
Yes. In summer, it takes about 1 week; in winter, around 2 weeks. It’s ready when the color turns a soft pink-beige and the koji can be easily crushed with your finger.
Keep it in a clean, airtight container in the refrigerator, and it’s best used within about 3 months.
Natural fermentation can slightly deepen the color or intensify the aroma. As long as there’s no unusual smell or mold, it’s fine. You can gently stir with a clean spoon if you like.
Onion Koji can flavor many dishes, such as Vegan Bolognese, Vegan Cream Pasta, Vegan Tuna Mayo, Vegan Béchamel Sauce, Vegan Borscht, Vegan Japanese Curry, and more. Think of it as a gentle, plant-based substitute for consommé cubes or vegetable broth in almost any recipe.
Koji is alive and breathing during fermentation. Make sure the lid isn’t on too tight, and check the color each day.
Fresh rice koji gives the best flavor, but dried koji can work too. Keep in mind that dried koji absorbs moisture differently, so you might need to adjust the amount slightly. I will update this page with exact instructions once I test it myself.
If you feel like whispering a thought, asking a question, or simply saying hello — the comment section is always open 📮
🍽 Recipes with Consomme Onion Koji
- Easy & Refreshing Tomato and Basil Vegan Pasta
- Harty Vegan Chickpea Minestrone Soup (Japanese-style Pork & Beans)
- Vegan Stir-fried Veggies & Whole Red Lentils with Ketchup-Based Sauce
- Vegan Borscht
- Vegan Chilled Baby Corn Soup
- Quick & Easy 3 Minutes Vegan Cup of Soup (Japanese-Style Cream of Mushroom)
- Simple & Nostalgic Vegan Japanese Curry Rice | Gluten-Free & Healthy
- Vegan Creamy Maitake Mushroom Pasta
- Vegan Spaghetti Bolognese with Lentils (No Meat, High Protein)
🖋 More Recipes with Onion
🌾 More Recipes with Koji
Koji-based umami boosters for vegan cooking:
📖 Recipe Card｜Printable
Homemade Vegan Consomme, Onion Koji｜Japanese Umami Seasoning
Equipment
- Grater OR Food processor OR Hand blender
- Bowl
- Spatula
- Spoon
- Glass container or Jar
Ingredients
- 300 g Fresh Onion
- 100 g Fresh Rice Koji
- 35 g Natural Salt
Instructions
- Prepare the onion: Grate the onion using a grater, food processor, or hand blender.300 g Fresh Onion
- Mix: In a bowl, combine the grated onion with fresh rice koji and salt. Mix well using a spatula.100 g Fresh Rice Koji35 g Natural Salt
- Transfer to jar: Place the mixture into a clean glass container or jar. Cover lightly with the lid or plastic wrap. Store out of direct sunlight.
- Observe & stir (optional): As the koji matures, the color may change. You can give it a gentle stir to evenly distribute color, though daily mixing isn’t required.
- Maturation: Wait until the mixture turns a beautiful pink-beige or beige and the koji grains can be easily crushed with your fingers. This typically takes 1 week in summer or 2 weeks in winter.
- Refrigerate: Close the lid tightly and store in the refrigerator. Best used within 3 months.
Notes
- When using, always stir from the bottom to distribute the salt and flavor evenly.
- Fresh rice koji gives the best flavor; dried koji works but may require slight adjustments.
- Do not worry if the color changes during maturation—it’s part of the natural process.
- Uses: Vegan Bolognese, Vegan Cream Pasta, Vegan Tuna Mayo, Vegan Béchamel Sauce, Vegan Borscht, Vegan Japanese Curry, etc.
- Maturation delay: Ensure the lid isn’t too tight; koji breathes while fermenting.
- Dried koji: Can be used, but fresh gives the best results.
If this recipe made its way into your kitchen, and you'd like to share that moment, feel free to tag @veginveganvegun or use #vegin_vegan_vegun.
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Ellie says
It was perfect for making Japanese curry, thank you!