Aspergillus oryzae (Yellow koji mold)
Aspergillus oryzae (Yellow koji)
Japanese: 黄麹菌（Aspergillus oryzae / A. sojae）
The most widely used koji mold in Japanese brewing. Used for miso, soy sauce, sake, and some shochu production, named 'yellow koji' for its yellowish-green spores.
Yellow koji mold stands at the very center of Japanese fermentation. Most koji molds used in brewing miso, soy sauce, and sake are classified as yellow koji.
Its spores are yellowish-green—a name distinguishing it from white and black koji. In culture, the color is subtle and delicate. It produces abundant amylase and protease, efficiently breaking down starches and proteins.
Taxonomically, it is broadly divided into Aspergillus oryzae (for miso and sake) and A. sojae (for soy sauce), though the boundary can be blurry. Centuries of selection by brewery masters have given rise to today's excellent strains.