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.
- Substrate must be cooked but not wet — excess moisture promotes bacterial contamination rather than koji growth. The grain should feel dry to the touch but be fully hydrated internally [VERIFY moisture content] - Incubation temperature: 30–33°C throughout the growth period. Below 28°C growth slows dramatically; above 35°C the mould dies and harmful bacteria proliferate [VERIFY temperature range] - Humidity: 70–85% relative humidity. The grain must stay moist enough for mycelium penetration but not so wet that bacterial contamination outcompetes the koji [VERIFY humidity] - Growth period: 40–50 hours for rice koji. The koji is ready when it is fully white, fragrant with a sweet chestnut aroma, and shows mycelium penetration throughout — not just on the surface [VERIFY time] - Shio koji (salt mixed with finished koji) is a versatile curing and flavouring agent — the enzymes remain active and continue developing flavour in whatever they contact [VERIFY ratio: approximately 1:1 koji to salt by weight] Decisive moment: The aroma at 40–48 hours — properly growing koji smells of sweet chestnuts, mushrooms, and clean fermentation. Off aromas (ammonia, acid, rot) indicate contamination. The mould should be completely white — any black, green, or pink colouration indicates non-koji growth and the batch must be discarded. Sensory tests: - Ready koji: completely white, sweet chestnut aroma, mycelium visible throughout grain cross-section, grain feels slightly warm from metabolic heat - Shio koji after 1 week: liquefied, deeply savoury, sweet, complex — not simply salty
- Substrate too wet — bacterial contamination outcompetes koji - Temperature too high — koji dies, harmful organisms flourish - Inadequate air circulation — CO2 builds up in the incubation chamber, slowing growth - Harvesting too early — amylase and protease enzyme content not yet at maximum - Contaminated equipment — koji spores are resilient but other organisms introduced through dirty tools will compete
MAANGCHI KOREAN — Second Batch KR-26 through KR-40