Shio Koji Marinated Mushrooms

In early 2019, we hosted a weekend-long event at the Daylesford Longhouse called Hakko, celebrating Japanese fermentation and preserves. We brought in Terada Masaru and Nancy Singleton Hachisu from Japan—both respected voices in traditional Japanese food culture. It was an ambitious undertaking, and the weekend itself was genuinely special: full of learning, wonderful food, and a roomful of people eager to deepen their understanding of fermentation.

One of the recipes that Nancy asked us to prepare on that weekend was these shio koji marinated mushrooms. Simple, elegant, and packed with umami, this demonstrates everything shio koji does well: transforming vegetables with minimal fuss, creating deep flavour through enzymatic action, and delivering that elusive fifth taste we call umami. So yummy. 

What is Shio Koji?

Shio koji is a traditional Japanese ingredient made from rice koji (rice inoculated with Aspergillus oryzae), salt, and water. As the mixture ferments, the koji's enzymes break down proteins and starches, creating a paste rich in umami, subtle sweetness, and the power to tenderise and enhance whatever it touches. It's been used in Japanese households for centuries, though it's experienced a renaissance in recent years as cooks discover its versatility.

The magic lies in those enzymes—particularly protease and amylase—which work to both tenderise proteins and develop complex flavours. When you marinate mushrooms (or meat, fish, or vegetables) in shio koji, you're not just adding salt; you're fundamentally transforming the ingredient's texture and taste.

Shio Koji Mushrooms

Serves 4 as a side dish

Ingredients:

• 400g mushrooms (shiitake, Swiss brown, oyster, or a mix)
• 2-3 tablespoons shio koji
• 1 tablespoon neutral oil (for pan-frying) or oil for brushing (if grilling)
• Optional: fresh herbs like shiso, parsley, or chives for garnish

Method:

1. Clean and prepare the mushrooms: Wipe mushrooms with a damp cloth rather than washing them (they'll release too much water when cooking otherwise). For larger mushrooms like shiitake or Swiss brown, cut into thick slices or halves. Leave smaller mushrooms whole.
2. Marinate: In a bowl, gently massage the shio koji into the mushrooms, ensuring each piece is lightly coated. You want a thin, even coverage—not a heavy coating. Let them sit for at least 20 minutes, or up to 2 hours at room temperature (or overnight in the refrigerator for deeper flavour).
3. To grill: Preheat your grill or barbecue to medium-high heat. Thread mushrooms onto skewers if desired, or use a grill basket. Brush lightly with oil. Grill for 3-4 minutes per side until golden and caramelised, with slight char marks.
4. To pan-fry: Heat a tablespoon of neutral oil in a large frying pan over medium-high heat. Add mushrooms in a single layer (work in batches if needed—crowding creates steam rather than caramelisation). Cook undisturbed for 3-4 minutes until golden, then flip and cook another 2-3 minutes.
5. Serve: Garnish with fresh herbs if desired. These are delicious warm or at room temperature.

Notes:

• The shio koji will create beautiful caramelisation as the sugars develop during cooking. Watch for burning, especially on the grill.
• Don't skip the resting time—those enzymes need time to work their magic.
• These mushrooms are excellent on rice, in grain bowls, alongside grilled meats, or simply as a side dish.

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Making Your Own Shio Koji

Ingredients:

• 200g rice koji (available at The Fermentary!)
• 60g sea salt
• 250-300ml filtered water

Method:

1. Combine rice koji and salt in a clean jar, mixing to distribute evenly.
2. Add water until the koji is just covered (it should be a porridge-like consistency).
3. Stir daily for 7-14 days at room temperature. The mixture will soften, become creamy, and develop a sweet, complex aroma.
4. Once the grains are very soft and easily crushed between your fingers, it's ready.
5. Store in the refrigerator for up to 6 months.

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Beyond Mushrooms: Quick Shio Koji Applications

Once you've made shio koji, you'll find endless uses for it:

Instant marinades (20 minutes - 2 hours):

• Chicken thighs or breasts: 1 tablespoon per piece, grill or roast
• Salmon or white fish: thin coating, pan-fry or bake
• Sliced eggplant or zucchini: massage in, then grill
• Tofu steaks: coat and pan-fry until golden

Longer marinades (4-24 hours):

• Pork chops or pork belly: deeply tenderising
• Whole fish: transformative for texture
• Root vegetables before roasting

As a seasoning:

• Stir into soups instead of salt (add at the end)
• Mix into salad dressings (2 parts oil, 1 part acid, 1 part shio koji)
• Toss with roasted vegetables fresh from the oven
• Stir through cooked grains or noodles

The ratio: As a general guide, use about 10% shio koji to the weight of your ingredient (e.g., 10g shio koji per 100g chicken).

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Why This Recipe Matters

What I've come to understand about shio koji is that it rewards trust—trust in the process, trust that enzymes will do their work quietly and efficiently, trust that simple ingredients treated properly can be extraordinary. Mushrooms marinated and cooked with shio koji are delcious - they burn a little quicker, taste of umami, of time and transformation, of enzymatic alchemy working below the surface.

Try it once, and if it isn't already - shio koji will become a permanent resident in your refrigerator.

Further reading: Nancy Singleton Hachisu's books Japanese Farm Food and Preserving the Japanese Way offer comprehensive guides to traditional Japanese techniques and remain valuable resources for home fermenters  - from an American who married a Japanese guy and has remained in Japan now for decades. We brought Nancy out several years ago to take part in Hakkō, our Japanese Ferment Festival held at The Daylesford Longhouse.

Our own local miso maker and educator - Yoko Nakazawa also attended Hakkō in 2019 as a teacher (she is Cooking with Koji on insta). Yoko has married an Australian and been living here for decades and making miso to sell at markets for years - has just written a book too - 'The Japanese Art of Pickling and Fermenting; Preserving vegetables and family traditions'.  My recommendation is Yoko's book. Nancy has actually garnered inspiration from Yoko's blog over the years, even acknowledging her in her own preserving book as a source of information x