Step 1

In a lidded container, combine koji and salt, breaking up any clumps of koji either with clean hands or a spoon. Add water and stir until mixture is well-combined and salt is dissolved, about 30 seconds.

Step 2

Cover container with lid and set aside to ferment at room temperature until koji mixture is thickened and smells sweet and funky, at least 7 days or up to 10; stir mixture once per day throughout this fermentation process. Once shio koji is fermented, transfer to refrigerator until ready to use. Shio koji can be refrigerated in an airtight container for up to 10 months.