Koji is the Japanese term for "cultured grain." Fermentation is a natural process that preserves and enriches food. For over 2000 years, the koji fermentation method has been used in Japan for making vinegar, miso, and soy sauce. Solgar EarthSource Koji Fermented Zinc starts by growing the koji culture on cooked rice. As the koji matures and ferments, it's enriched with zinc. Then, it's harvested and processed into powdered Koji Zinc. This food-based bioavailable zinc is an important immune supporting nutrient.