It’s impossible to imagine Japanese meals without soy sauce, or the umami-rich fermented bean paste called miso, or the rice-based spirit known as sake. Which means that Japanese cuisine depends on the one fungus that enables the fermentation of all these delicious foods: koji. Today, American chefs are discovering what Asian cooks have known for centuries, that koji is a microbial powerhouse with seemingly magical abilities to completely transform food. But how does a mold from a family of microbes known for their toxicity turn salty, mashed beans into sticky, succulent miso? How did koji make its way from Japan to the U.S.? And how might the weird and wonderful ways chefs in the U.S. are now using koji transform the American dinner table, too?
Koji, or, as it’s known in scientific circles, Aspergillus oryzae, was domesticated by humans around 9,000 years ago. The fungus’s closest relatives can be deadly, due to the chemicals they produce to kill off microbial competitors. But, fortunately for our taste buds, a random nontoxic mutation likely landed on some damp leftover grains in Asia, and humans noticed that the fuzzy mold, with its intoxicating scent of grapefruit and flowers, also turned those grains into a literally intoxicating drink. (Our ancestors wouldn’t have known that this happened because koji broke down the starch enough to let yeast ferment the newly freed sugars into alcohol, but they’d have enjoyed the results.) Delighted, they probably encouraged the mold to grow on other left-over grains, gradually domesticating it by giving it a cushy home and caring for it over generations.