You may have heard of countries having a national bird, national flower, or even national food, but did you know that Japan has a national fungus? Indeed, Japan’s national fungus is none other than the humble koji mold-- named such because of the integral role it plays in creating many of the flavors that make the backbone of Japanese cuisine. Miso, sake, mirin, and Japanese soy sauce all owe some portion of their distinct tastes to koji mold, as its unusual properties add a certain subtle specialness to all of these key Japanese ingredients.
Koji mold, known scientifically as aspergillus oryzae, is a type of mold that grows naturally on rice plants, and historically, cooked rice grains left unattended (today, a more scientific approach is favored; beds of cooked rice, wheat and soybeans are purposely inoculated with spores, and their growth is monitored very precisely). Most species of aspergillus mold produce spores that are highly toxic and can lead to respiratory infections among people who are exposed, but koji mold is somewhat special in this regard. Unlike it’s deadly cousin, the dreaded black mold that tends to flourish in basements that are too wet, koji mold’s spores are completely harmless to humans, making it ideally suited as a fermentation agent.
In a culinary application, koji mold works in a peculiar way. The mold filaments secrete enzymes to make the medium it grows on more easily usable. These enzymes break carbohydrates down into sugars, and proteins down into their constituent amino acids. This process results in two things: first, the release of a wonderful, complex and subtle aroma from the mold, and second, a substantial uptick in the balance of compounds that human beings find particularly flavorful. In other words, koji