Shio koji is a slurry using koji rice, water, and salt that is left to ferment. The mixture matures with time into a sweet, salty, umami porridge that is perfect for using as a marinade as the enzymes in the koji asssist in tenderizing the ingredients. If you’re not familiar with koji, it is a fungus, usually grown on a grain with certain enzymes that are responsible for the unique flavors in products like miso, sake, and shoyu. I like to use the shio for almost any meat, including all poultry or even different vegetables to add another dimension to my cooking.
Making shio is very easy. I combine dry koji to water at a 1:2 ratio. Add 1 tbs salt per 2 cups of mixture, or to your preference. Pop it all in a mason jar with lid fixed snug, give it a shake, and let it do its thing at room temperature.
If you’d like to get well acquainted with it, taste it every couple of days and note how it changes. After about 2 weeks you should be at a decent spot of maturity to do some marinating. However feel free to go as long as you wish.