What Is Koji? (麹)

Koji is grain or beans carrying a cultivated mould, Aspergillus oryzae - the starter behind miso, shoyu, amazake and sake.

What it is	Steamed rice, barley or soybeans inoculated with Aspergillus oryzae spores (tane-koji) and held warm until the grains are covered in white mycelium
What it does	Its enzymes break starch into sugars (amylase) and protein into amino acids (proteases) - the source of sweetness and savoury depth
Standing	In 2006 the Brewing Society of Japan described Aspergillus oryzae as Japan's 'national fungus' (kokkin)

Almost every Japanese fermented seasoning starts with koji. The mould itself is not eaten as a separate food so much as used as a living tool: once koji has done its enzymatic work in a salted mash, the result becomes miso, soy sauce, mirin seasoning or sake, depending on what it is combined with.

Koji is made, not gathered. Specialist koji starters (moyashi) have been produced for centuries - Kyoto's Hishiroku, a koji starter maker with about 300 years of history, is one of the best known. The spore type is chosen for the job: strains for miso, for shoyu and for sake differ in their enzyme balance.

This guide covers koji as a food ingredient - the fresh and dried koji sold for cooking, and the seasonings made from it. The brewing-technical side of koji for sake belongs to our sake guide; here the focus is the kitchen.

What Is Koji? (麹)

See also