Shoyu Koji
Gloopy, rich, and full of flavor after about a month in the fridge. Gets better with age.
A natural, umami-rich seasoning that’s toddler-friendly, gut-friendly, and full of gentle flavor.
Shoyu koji (醬油麹) is a naturally fermented seasoning made by combining naturally brewed (古式醤油) soy sauce and rice koji — a traditional Japanese culture used in miso and sake. It’s rich in enzymes that break down proteins and starches, making food more digestible and flavorful without needing salt bombs or MSG.
Shoyu Koji Recipe
Ingredients:
100g dried rice koji (if buying in Hong Kong, I use this one)
100ml naturally-brewed Japanese soy sauce (I bought this one in Tokyo)
250g glass jar with lid
Instructions:
Clean the glass jar properly
Wash with gentle, unscented soap, and disinfect with boiling water. Turn upside-down and let air dry to avoid contaminants from dish towels.Break up the rice koji
Gently crumble the koji with clean hands or pulse it once in a food processor if very clumpy.Mix with soy sauce
In a clean glass jar, combine the rice koji and soy sauce. Stir well until every grain is coated.Ferment
Cover loosely (with a cloth or lid slightly ajar) and let it sit at room temperature (20-28 degrees celsius) out of sunlight for 5–7 days, stirring once a day. It will smell savory and slightly sweet.Store
After fermentation, seal and store in the fridge with lid loose. It will continue to develop flavor and last for 3–6 months.
How to Use Shoyu Koji:
Marinate chicken, beef, or fish for 30 mins to a few hours
Stir into minced meat for a gentle soy flavor
Drizzle on rice or veggies like a toddler-safe soy sauce
Add to soup broth or congee for extra depth
(Just 1 tsp goes a long way!)
Note for Toddlers:
Because it’s fermented and has a lower sodium profile than regular soy sauce, shoyu koji is a great seasoning from around 10–12 months, in moderation. As always, check the ingredient list to avoid soy sauces with alcohol or chemical preservatives.
Note for Hong Kong readers on choosing soy sauce:
When making shoyu koji, it’s important to choose the right kind of soy sauce. Go for a naturally brewed, “頭抽” (first press) or “生抽” (light soy sauce) without additives. Look for labels that say 「古式」 (Koshiki, traditional brewing) or 「天然醸造」 (naturally brewed) - these indicate slow fermentation with just soybeans, wheat, water, and salt. Avoid dark soy sauce (“老抽”), which is thicker, sweeter, and often contains caramel coloring - it will overpower the koji fermentation. Also skip “seasoned soy sauces” made for dumplings or sashimi, as they usually contain sugar, MSG, or other flavorings that can throw off the fermentation.
Examples of naturally brewed soy sauce you can use in HK:
