Koji is the fluffy white-and-gold mould Aspergillus oryzae grown deliberately on steamed grains — most often rice, but also barley and soybeans — to make the fermentation starter behind miso, soy sauce, sake, mirin and amazake. Named a "national fungus" of Japan, it is arguably the most important culinary mould on Earth: as it grows it floods its grain with enzymes that break starch into sweetness and protein into savoury, umami-rich amino acids, the biochemical engine of much of East Asian cuisine.