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 mold causes food to taste and smell better. Koji mold can be cultivated on basically anything starchy-- rice, soybeans and toasted wheat are traditional, but koji also thrives on barely, rye, and even popped popcorn. Through the actions of its filaments, koji naturally enhances the sweet and umami flavoring of whatever it grows upon.
In commercial production of koji-fermented foods, different strains of koji, combined with different growth mediums are used to produce variations in flavor, aroma and texture. Three commonly used strains of Koji are yellow, white, and black varieties. Yellow koji is the most sensitive strain to variation in temperature, and as such requires great skill to properly cultivate. However, this difficulty is rewarded by the flavor it gives-- one that is rich, fruity and refreshing. Black and white koji are more hardy, requiring less precise monitoring. Black koji produces higher quantities of citric acid, which helps keep its medium from prematurely spoiling and gives a rich aroma, and sweet, mellow flavor. It’s biggest drawback is the color of its spores. Black koji’s spores are, as its name suggests, deep black and have a tendency to cover nearby exposed surfaces with a fine layer of charcoal colored dust. White koji is the most commercially popular today. It is the easiest and cleanest to cultivate, and it works quickly to break down its growth medium, adding a sweet and refreshing taste.
Experiencing the magic of koji at home is actually quite simple. Aside from cultivating it yourself, a process that, though usually not difficult, does require some time and monitoring, ready to use rice rice koji can be purchased right here at Maido. We have a few varieties to choose from. Cold Mountain Liquid Koji and Dry Koji are the least processed types. Each one is made from koji-fermented rice with a small amount of salt, and, in the case of liquid koji, water added for flavor and texture enhancement. Each of these koji can be used directly as marinades and seasonings. Scoop a spoonful into a stir-fry, or cup of miso soup, and, in a short time, experience the flavor enhancing powers of this little mold. The third type of koji we carry is Liquid Shio Koji. This koji has been substantially diluted with salt and water, which gives it a finer, more even texture, and makes it ideal for adding straight to sauces or using on its own as a marinade. We even use this particular one on-site in our own kitchen. Chicken for our teriyaki and karaage dishes is marinated overnight using only liquid shio-koji! The result is a substantially more flavorful chicken, that, through the action of the salt, holds its moisture content well.
With such a strong, flavor enhancing power, it is obvious to see how koji mold gained its prominence within, not only Japanese cuisine, but Asian cooking in general. It’s importance in creating favorite flavors makes its position as Japan’s national fungus not only accurate, but deserved.