In a storage container such as a glass jar with a lid, mix water and salt well until salt is completely dissolved.
Add dry koji and mix with the salt & water. Put the lid on but do not close the container tightly. Carbon dioxide produced during fermentation should be able to escape.
Leave the container at the room temperature, stirring the content once a day.
In one week to 10 days, when the koji becomes creamy, it’s ready for use.
Koji Marinated Pork Loin
Combine shio koji, garlic, and ginger well.
Put the pork fillets and koji marinade together in a ziploc bag. Massage the pork, making sure to squeeze all the air out of the bag. Seal the bag and refrigerate it for 8 hours or overnight.
Take the pork fillet out of the bag and wipe off excess marinade with paper towel, as the koji tends to burn quickly on a pan.
Heat cooking oil in a cast iron or stainless steel pan over medium-high heat. Place the pork in the pan.
While cooking one side put the lid on and turn the heat down to medium. Cook for about 5 minutes.
Flip the pork, put the lid back on, and cook the other side for another 5 minutes or longer until the meat is cooked through.