How to Make Shio Koji

If you're new to fermentation and feeling intimidated by multi-week projects, temperature control, or complex equipment, shio koji is your entry point. It's arguably the easiest ferment you can make: just three ingredients, a jar, and a week of daily stirring. No heating, no pH testing, no special vessels. And yet, the results are transformative—a creamy, umami-rich paste that will change how you cook vegetables, meat, and fish.

Despite being rooted in centuries of Japanese tradition, shio koji as we know it today is surprisingly new to home kitchens, even in Japan. Its recent renaissance makes it both ancient and modern—a technique rediscovered and democratised for contemporary cooks.

What is Shio Koji?

Shio koji (塩麹) translates simply as "salt koji." It's a fermented seasoning made from three ingredients:

• Rice koji (kome koji): steamed rice inoculated with Aspergillus oryzae, the mould culture used to make sake, miso, soy sauce, and mirin
• Salt: typically sea salt
• Water: clean, unchlorinated water

When you combine these ingredients and let them ferment at room temperature for 7-14 days, the koji's enzymes—particularly protease (which breaks down proteins) and amylase (which breaks down starches)—begin working their magic. The mixture softens, becomes creamy, and develops a sweet, slightly funky, deeply umami aroma. What you're left with is a living seasoning paste that both flavours and tenderises whatever it touches.

Unlike miso, which can take months or years, shio koji is ready in about a week. Unlike pickling, there's no vinegar or long brining time. It's genuinely one of the most beginner-friendly ferments you can attempt.

A Brief History: Old Technique, New Trend

Shio koji isn't new—it's been used in Japanese households for centuries as a pickling medium and seasoning. But for much of modern history, it remained a somewhat obscure ingredient, overshadowed by soy sauce and miso in everyday cooking. I certainly didn't come into contact with it when I was living there. 

Shio Koji kind of had a 'glow up' and came into the spotlight around 2011-2012 when Japanese cookbook author and chef Koji Nakamura published Shio Koji de Yaseru Recipe ("Shio Koji Diet Recipes"), which sparked a nationwide boom. Suddenly, shio koji was everywhere in Japan—in home kitchens, restaurants, and commercial products. The trend highlighted what traditional cooks had always known: shio koji is incredibly versatile, adds complex umami without heaviness, and makes cooking easier, not harder.

From Japan, the trend spread internationally. Chefs and home fermenters in Australia, the US, and Europe began experimenting with it, discovering its potential beyond Japanese cuisine. Today, it's used to marinate lamb, tenderise chicken, season salad dressings, and even make Western-style pickles.

For those of us passionate about fermentation, shio koji represents something important: it's accessible. You don't need years of experience or specialized knowledge. You need koji, salt, water, and a willingness to stir a jar once a day.

How to Make Shio Koji

Ingredients:

• 200g rice koji (fresh or dried—both work)
• 60g sea salt (about 30% of the koji's weight)
• 250-300ml filtered or dechlorinated water

Equipment:

• Clean glass jar (500-750ml capacity)
• Spoon for stirring
• Breathable cover (cloth, paper towel, or loose lid)

Method:

1. Combine koji and salt: In your jar, mix the rice koji and salt together thoroughly. If you're using fresh koji, it will feel moist and slightly sticky. If using dried koji, it will look like broken rice grains. Either way, make sure the salt is evenly distributed.
2. Add water: Pour in enough water to just cover the koji mixture. It should have a porridge-like consistency—thick, but with visible liquid. Stir well.
3. Cover loosely: You want airflow, but you also want to keep dust and insects out. Use a cloth secured with a rubber band, a paper towel, or a jar lid rested on top (not screwed on tight).
4. Ferment at room temperature: Place the jar somewhere at room temperature, out of direct sunlight. Ideal temperature is 18-25°C, but it's quite forgiving.
5. Stir daily: This is the only active work required. Once a day, give your shio koji a good stir. You'll notice changes:
   • Days 1-3: The mixture looks grainy, smells mildly sweet and yeasty
   • Days 4-7: The koji grains soften, the mixture becomes creamier, and the aroma deepens—sweet, funky, almost chestnut-like
   • Days 7-10: The grains are very soft (you can crush them easily between your fingers), and the paste is thick and creamy
   • Days 10-14: The flavour mellows and becomes more complex
6. Taste and decide: After 7 days, taste it. If the koji grains are soft and the flavour is pleasantly umami-rich and sweet, it's ready. If it's still quite salty or the grains are firm, let it go a few more days. There's no exact timeline—trust your senses.
7. Refrigerate: Once it's ready, transfer to the fridge. The cold slows fermentation dramatically. Shio koji will keep for 6 months or longer refrigerated.

Troubleshooting:

Too thick? Add a tablespoon of water and stir.
Too thin? That's fine—it just means it's more liquid. It will still work beautifully.
Smells alcoholic or slightly sour? Normal! That's fermentation at work.
Smells rotten or like gym socks? Not normal. Discard and start again, ensuring your jar was clean and your water unchlorinated.
White fuzzy mould on top? If it's a thin white bloom, that's likely kahm yeast—harmless, but skim it off. If it's pink, green, or black, discard.

The Science: What's Actually Happening

When you make shio koji, you're creating an environment where Aspergillus oryzae can thrive. This mould has been cultivated in Japan for over a thousand years and is prized for its enzymatic power.

Protease enzymes break down proteins into amino acids, which are the building blocks of umami. This is why shio koji makes meat and fish taste more savory and intense—it's literally unlocking glutamates and other amino acids.

Amylase enzymes break down starches into simple sugars, which is why shio koji has that characteristic sweetness, even though there's no added sugar. Those sugars also caramelise beautifully when you grill or roast foods marinated in shio koji.

The salt serves multiple purposes: it controls the fermentation rate, prevents unwanted bacteria from taking hold, and seasons the final paste. The 30% salt ratio (relative to the koji's weight) is high enough to be preservative but low enough to let fermentation happen.

How to Use Shio Koji

Once you've made it, shio koji becomes a kitchen staple. Here's a quick overview:

As a marinade:
Use about 10% shio koji relative to the weight of your protein or vegetables (e.g., 10g shio koji per 100g chicken). Marinate for 20 minutes to overnight, then cook as usual. The enzymes tenderise while adding flavor.

As a seasoning:
Stir a spoonful into soups, dressings, or grain dishes in place of salt. It adds depth and complexity beyond what salt alone can achieve.

As a pickle:
Massage shio koji into sliced cucumbers, daikon, or cabbage and let sit for a few hours. The result is a quick pickle with umami punch.

Examples:

• Chicken thighs marinated in shio koji, then grilled
• Salmon fillets brushed with shio koji, pan-fried until caramelised
• Mushrooms coated in shio koji and charred (see our [Shio Koji Mushroom recipe])
• Roasted cauliflower tossed with shio koji before roasting
• Sliced eggplant marinated and grilled for summer barbecues

Why Shio Koji Belongs in Your Kitchen

Shio koji is forgiving. It's hard to mess up. It requires minimal equipment, no technical skill, and delivers results that make you look like a far more experienced cook than you might be. It bridges traditional Japanese technique with modern, intuitive home cooking.

For those new to fermentation, it's proof that fermentation doesn't have to be scary or precious. It can be as simple as stirring a jar once a day and tasting as you go. And once you've made it, you'll understand why it's become a staple in kitchens far beyond Japan.

Rice koji available at [The Fermentary shop link].
Want to see shio koji in action? Try our [Shio Koji Marinated Mushrooms recipe].