Japanese Ingredient Highlight: Shio koji (塩麹, 塩糀). A century-old natural seasoning used in Japanese cooking to marinate, tenderize, and enhance umami flavor of a dish. Learn more about this all-purpose seasoning.
In a large bowl, break 200 g rice koji and separate the koji grains into smaller pieces.
Rub the koji firmly in your hands to separate into individual grains.
Rub the koji until aromatic, add 4–5 Tbsp sea salt, and mix all together.
Add 1 cup water. If necessary, add more water if it doesn‘t cover the surface of the koji. Rub the koji with your hands.
Transfer to sterilized jar(s)/container with a lid. Make sure the shio koji is submerged in water; if not, add more water.
Ferment the shio koji at room temperature, open the lid and mix it once a day for 1 week during the summer and 2 weeks during the winter (as warm temperature speeds up the ripening process). Add a bit of water if the shio koji is too hard. It might taste salty at the beginning, but it will gradually become mild. Shio Koji will become thicker and begin to smell sweet from the fermentation.
To Store
Store in the refrigerator for up to 6 months.
Notes
Koji: The majority of koji you find at stores will appear lighter in color than this brand of koji that I use, which is slightly yellow. The yellow color comes from koji mold, and some are yellow and some are brown. Depending on the brand/company, they may mix different kinds of koji molds to create a more complex flavor. You see more white koji in stores as they look “prettier” (source).