Koji starters is the spores of aspergillus oryzae used in fermented foods such as soy sauce, miso and sake. Aspergillus oryzae was certified to a "national fungus" (kokkin) by the Brewing Society of Japan in 2006.
Koji is heat-denatured ingredients such as steamed rice and barley inoculated with Koji starters (aspergillus oryzae), which is cultured for about 3 days under the control of temperature and humidity. Because koji contains enzymes produced by aspergillus oryzae, its enzyme action decomposes starch and protein, producing sugar and amino acid which serves for the nutrition of taste ingredients, yeast, etc.
The details are this