Koji: Aspergillus Oryzae as Flavour Engine

Koji mould (Aspergillus oryzae) is the foundation of Japanese fermentation — the organism responsible for sake, miso, soy sauce, mirin, and rice vinegar. Noma's fermentation laboratory, under the direction of David Zilber, applied koji beyond its traditional Japanese applications to European ingredients — growing it on barley, rye bread, and proteins to produce accelerated umami development. The result was a body of work that brought koji into the global chef conversation.

Aspergillus oryzae spores inoculated onto a cooked starch substrate (rice, barley, bread, corn) and incubated at specific temperature and humidity until the mycelium penetrates the grain and produces enzymes — primarily amylases (which break down starch into sugars) and proteases (which break down proteins into amino acids and glutamates). The resulting koji is then used as an ingredient, a fermentation starter, or a curing agent.

Koji develops flavour through enzyme activity, not through heat or acid. It produces glutamates (umami), sugars (sweetness), and complex aromatic compounds simultaneously. Shio koji applied to protein for 24–48 hours produces a Maillard response during cooking that is faster and more intense than unsalted protein — the sugars produced by amylase activity brown more readily at the surface.