Shio koji is rice koji mixed with salt — a living enzyme marinade. The proteases in the koji partially break down the surface proteins of the fish over 24 hours: the result is tender, deeply seasoned salmon that caramelizes far better than anything marinated in plain salt.
What You Need
- 2 salmon fillets (skin-on, 150-180g each)
- 3 tbsp shio koji (store-bought or homemade)
- Optional: lemon, fresh dill, or perilla to serve
Shio koji is available at Japanese grocery stores and increasingly at health food stores. Homemade: mix 200g rice koji + 20g salt + 160ml water, stir daily, ready in 7-10 days at room temperature.
Method
1. Coat: Pat salmon dry. Coat both sides with shio koji — a thin, even layer. Place in a container or zip-lock bag.
2. Refrigerate 24 hours: This is the critical step. 12 hours minimum; 24 is optimal. The enzymes need time. Do not skip or rush this.
3. Scrape off excess koji before cooking: The koji paste will burn if left on. Scrape off most of it (not all — a thin coating is fine and adds caramelization).
4. Cook: Two options:
Pan-sear: Heat a heavy pan over medium-high. Add a small amount of oil. Place salmon skin-side down. Press lightly for 10 seconds. Cook 4-5 minutes until skin is crisp. Flip. Cook 1-2 minutes until just cooked through. The koji coating will create a visibly deeper golden-brown crust than regular salmon.
Oven: 200°C (400°F), 12-15 minutes on a foil-lined sheet. The koji caramelizes across the entire surface without requiring any attention.
Notes
- The caramelization difference is real — side-by-side comparison with the same salmon marinated in plain salt shows visibly better browning from the shio koji amino acids (Maillard reaction requires both amino acids and reducing sugars, both provided by koji).
- Do not over-marinate beyond 36 hours for thin fillets — the enzymes will break the surface texture down too far.
- Works identically on chicken thighs, pork chops, and firm white fish.