Last week my friend Mayumi came to visit for a few days and brought me a gift for my kitchen- a pouch of shio koji. Shio koji, for those who are unfamiliar, is a rice malt that has been fermented with sea salt. The rice malt (koji) is made from rice that has been inoculated with the spores of a benign mold called Aspergillus oryzae. Shio koji looks like a white porridge-like paste and imparts a sweet, floral aroma. Koji itself has been around for centuries. It's used by sake brewers and makers of soy sauce, mirin and miso. In the past two years, however, it has experienced a huge resurgence and become a popular pantry staple in Japanese kitchens and is now gaining a following in the US. Shio koji has a mild taste that can be best described as a subtle combination of sweet and salty. It works great as a salt substitute and when added to dishes, this versatile seasoning packs a rich umami punch. You can use it to enhance all kinds of foods- you can use it to marinate and tenderize meats (it's supposedly fantastic on roasted chicken), season fish and vegetables, and as a seasoning base for sauces, soups and dressings. Some people even mix shio koji into baked goods or use it to make sausage. Mayumi told me one of her favorite uses for shio koji is marinating firm tofu in it. She presses the excess moisture out of the tofu, then rubs the shio koji on the tofu, wraps it in plastic and then lets it sit, refrigerated, for about 5 days. The tofu takes on a faux cheese like texture (creamy and dense) and tastes great spread on crackers. Shio koji is also great for making "quick" pickles.
Mayumi and I used some to "marinate" our sashimi Thursday night and I did find that the seasoning enhanced the flavors of the tuna noticeably.
Besides being easy to use, shio koji is nutritious and great for the digestive system. It's rich in enzymes and amino acids. Also, the fermentation process increases the amount of vitamins B1, B2, B6 and lactic acid.
You can buy shio koji premade in the refrigerated section of your Japanese grocery store or make your own. To make your own batch, you would need to buy the granulated rice koji (kome koji), add sea salt and water then allow the mixture to ferment for a week. The finished product will keep for a few months, refrigerated. In addition to shio koji, there's also shoyu koji (koji mixed with soy sauce instead of salt) and ama koji (sweet koji). Shoyu koji is great on fish. We used some shoyu koji tonight on some salmon filets and it was delicious. I just covered 2 filets with a tablespoon of shoyu koji each and placed them in a Ziploc bag to marinate for about 4-5 hours. When dinnertime rolled around, I removed the fillets from the bag and placed them on a foil lined baking sheet and broiled them on high for 8-9 minutes on one side and about 3-4 minutes on the other. Shoyu koji burns easily so I kept a close eye on the salmon. The fillets came out perfect- the shoyu koji kept the fillets moist while crisping up the skin nicely and it seasoned and sweetened the fish itself.