Cover the surface of the meat with koji rice, and leave it in the refrigerator for 3 to 5 days. Then remove the koji rice and cook the meat to the desired temperature. You will achieve a dry-aging effect equivalent to 15 to 20 days.
You can make AMAZAKE (a paste made from koji rice) with 1 part koji rice, 1 part water, and 2% salt. Follow the same process as mentioned earlier for easier removal of the koji rice.