Photo: Forrest O., CC BY-SA 2.0 (via Wikimedia Commons)

Koji Mold

Aspergillus oryzae

Also known as Koji, Tane-koji (spore starter), Yellow koji mold, Rice mold

At a glance

Family

Aspergillaceae

Type

Filamentous fungus (mold), domesticated for fermentation

Parts used

Whole mycelium and spores, grown on steamed rice, barley, or soybeans

Size

Microscopic organism; visible colonies form a soft, cottony, pale gold to greenish mat over its growing medium within one to two days

Bloom

None in the plant sense. Aspergillus oryzae reproduces by releasing clouds of dusty conidia (asexual spores) once its mycelium matures

Habitat

Not found growing wild in any meaningful sense today. It is a long-domesticated descendant of wild soil and grain molds native to East Asia, now propagated entirely in controlled, warm, humid fermentation rooms

Acquisition

Buy

Traditional remedies in HerbSense

Key benefits

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Unlocks grain and bean nutrients

Aids traditional food digestion

Builds savory fermented flavor

Rich source of active enzymes

Traditional uses

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For well over a thousand years, this quiet gold-dusted mold has been the workhorse behind some of East Asia's most treasured foods, coaxed onto steamed rice or soybeans to become the starter for miso, soy sauce, sake, mirin, and rice vinegar. Japanese brewers and cooks learned to cultivate it so carefully, and valued it so highly, that in 2006 the Brewing Society of Japan named it the country's official kokkin, or national fungus. Traditionally, foods fermented with this mold, especially amazake and well-aged miso, have been taken as gentle digestive tonics, believed to ease the breakdown of rice and soy and to leave the stomach feeling lighter after a meal. Its enzymes were, in effect, the original food processors, transforming plain starch and protein into something sweeter, deeper, and easier for the body to take in.

How to grow & use it

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Pairs well with

✦Soybeans, for making miso and traditional soy sauce
✦Short-grain rice, for sake, amazake, and mirin
✦Barley, for rustic mugi-style miso

Substitutes

✦Aspergillus sojae, a closely related koji mold favored for some soy sauce styles
✦Rhizopus oryzae, the mold used to ferment tempeh, offering a different but comparable fermentation role

Choose it when

“When you want to coax sweetness, depth, and life out of humble grain and bean, the old and patient way.”

Did you know?

In 2006, the Brewing Society of Japan formally declared Aspergillus oryzae the country's kokkin, or national fungus, an honor that recognizes just how central this quiet mold has been to Japanese food and drink for over a thousand years.

Safety

Koji mold used in traditional fermentation is safe and, unlike wild relatives, does not produce aflatoxins. Raw spore powder can irritate the lungs, so people with mold allergies, asthma, or weakened immune systems should avoid handling it directly.