Koji-Marinated Salmon
Cookbook author Sonoko Sakai calls this her “‘no-recipe’ salmon dish. It’s adapted from her 2019 book Japanese Home Cooking: Simple Meals, Authentic Flavors, which we reviewed in June 2020. Simple yet delicious, it’s a great weeknight main course that can be gotten to the table in about 15 minutes (because you marinated the fillets the previous day or evening). It’s also the perfect centerpiece of a bento box or topping for ochazuke (rice tea soup) or — if you’re up for a cross-cultural adventure — a Vietnamese Rice Noodle Salad Bowl.
The recipe relies on shio koji — fermented koji salt — which you can buy in a Japanese supermarket or make yourself (instructions follow the salmon recipe). It’s a great to have lurking in your fridge (where it’ll last three months) for simple weeknight dishes like this. It’s also useful in case you have some fish you’d planned to cook that evening, but your plans change; slap on the marinade and you have a three-day window in which you can broil and eat it.
As nice as the salmon turns out with 24-hour shio-koji marination, if you let it cure for two days, it’s even more remarkable; the flavors concentrate more and the texture does something wonderful, a little velvety almost. We highly recommend the 2-day cure, rather than just over, if possible.
You can also use shio koji as a marinade in this way for other fish, Sakai points out, “such as mahi-mahi, yellowtail, opah, ocean whitefish, snapper, halibut, cod, scallops, squid or shrimp, as well as for meat including pork, chicken and beef.”
For the garnish, traditionally a Japanese grater called an oroshi-ki is used to grate daikon and ginger, but a fine Microplane grater works too.
Makes 4 servings.
Ingredients
3 tablespoons Shio Koji (see recipe below)
4 salmon fillets, about 1 1/2 pounds total
Canola or other neutral oil for brushing the fillets
For the garnish
6 ounces daikon, peeled and grated
1 tablespoon grated ginger
Instructions
1. Evenly spread the shio koji all over the salmon fillets, including the skin, and let them marinate in the refrigerator overnight or up to 3 days. The longer the fish marinates, the saltier it will become.
2. When you are ready to cook the salmon, position the top rack of your oven about 7 inches from the broiler and preheat the broiler. Line a rimmed baking sheet with aluminum foil.
3. Wipe off the shio koji with a paper towel or give the fish a quick rinse and then wipe down with a paper towel. Brush the fillets with oil and place them skin-side down on the prepared baking sheet. Broil for 5 to 6 minutes, until the fish is lightly browned and you can flake it easily with a fork. Serve with the grated daikon and ginger.
Shio Koji (Fermented Koji Salt)
Find dried rice koji in the refrigerated section of Japanese supermarkets, or online. It takes five days to ferment, and will keep in the refrigerator for up to 3 months.
Makes about 2 1/2 pounds.
Ingredients
1 pound dried brown or white rice koji
8 tablespoons sea salt
2 1/2 cups hot water (140 degrees F/60 degrees C)
Instructions
1. If the koji granules are whole (meaning they look like rice), grind them in a food processor until they are about half their size. In a large bowl, combine the rice koji with the salt and mix well.
2. Add the hot water and rub the granules with your hands. Transfer to a container with a lid to let it ferment at room temperature for 5 days. Stir with a spatula once a day. The shio koji will become thicker and creamier, and it will begin to smell like sweet miso from the fermentation process. You can make a creamy shio koji out of some or all of it by processing it using a food processor until smooth, or you can use it in its grainer form. The shio koji keeps for up to three months in the refrigerator.
Koji-Marinated Salmon
Ingredients
- 3 tablespoons Shio Koji (see recipe below)
- 4 salmon fillets, about 1 1/2 pounds total
- Canola or other neutral oil for brushing the fillets
- FOR THE GARNISH
- 6 ounces daikon, peeled and grated
- 1 tablespoon grated ginger
- 1 pound dried brown or white rice koji
- 8 tablespoons sea salt
- 2 1/2 cups hot water (140 degrees F/60 degrees C)
Instructions
- Evenly spread the shio koji all over the salmon fillets, including the skin, and let them marinate in the refrigerator overnight or up to 3 days. The longer the fish marinates, the saltier it will become.
- When you are ready to cook the salmon, position the top rack of your oven about 7 inches from the broiler and preheat the broiler. Line a rimmed baking sheet with aluminum foil.
- Wipe off the shio koji with a paper towel or give the fish a quick rinse and then wipe down with a paper towel. Brush the fillets with oil and place them skin-side down on the prepared baking sheet. Broil for 5 to 6 minutes, until the fish is lightly browned and you can flake it easily with a fork. Serve with the grated daikon and ginger.
- If the koji granules are whole (meaning they look like rice), grind them in a food processor until they are about half their size. In a large bowl, combine the rice koji with the salt and mix well.
- Add the hot water and rub the granules with your hands. Transfer to a container with a lid to let it ferment at room temperature for 5 days. Stir with a spatula once a day. The shio koji will become thicker and creamier, and it will begin to smell like sweet miso from the fermentation process. You can make a creamy shio koji out of some or all of it by processing it using a food processor until smooth, or you can use it in its grainer form. The shio koji keeps for up to three months in the refrigerator.
Notes:
Find dried rice koji in the refrigerated section of Japanese supermarkets, or online. It takes five days to ferment, and will keep in the refrigerator for up to 3 months. The koji salt sub-recipe makes about 2 1/2 pounds of Fermented Koji Salt.
Recipe notes
• We tested this twice — the first time marinating for 24 hours and the second time marinating for 48 hours. While the 24-hour cure gave a very good result, the 48-cure was much more impressive, resulting in more concentrated flavor and a more velvety texture. We haven’t yet tried a 72-hour cure; we will update when and if we do.