Koji: An Ancient Mold and Its Modern Renaissance

Rediscover the Japanese culinary wonder that’s making its way into the contemporary spotlight.

| Fall 2019

koji-closer 
Close up of koji.

For most people, including the word “mold” in the culinary vocabulary sounds like the opposite of delicious. But for fermenters, lovers of cheese, and curators of salami, mold worship is a kindred character quirk. Aspergillus oryzae — or koji, as it’s been called for centuries in Japan — enjoys one of the most storied and multifaceted relationships with humans of any of our micro-epicurean allies. In this article, and the following articles in this series, we’ll explore koji as thoroughly as possible for the nerds around the incubator. What is koji; how does it produce a huge variety of flavors; how can we discover its potential in the kitchen; and where is our partnership with this mold headed?

Meet the Mold

Koji is a filamentous mold, much like the type you might find growing on bread or oranges. Molds are fungi, and fungi attach themselves to their homes via hyphae (singular: hypha). Think of hyphae to fungi like roots to a plant. The individual hypha together make up many hyphae, and the network of hyphae is called a mycelium. A. oryzae makes its white to yellow-green network of fungal hyphae, or mycelial mat, on the surface of foods. Its favorite substrate is grain, so it’s aided the fermentation of rice, barley, and red beans for centuries. It’s predominantly associated with Japanese cuisine; its name comes from the culture, and its uses and flavor are key throughout the cuisine. Koji is a crucial component of miso, soy sauce, and sake, just to name a few foods with which most people are familiar. This friendly, multifaceted mold unlocks the promise of possibility in the kitchen.

jeremy-umansky
Jeremy Umansky experiments with koji in his development of "vegan charcuterie." He believes that you can use the mold to put a vegetable through the same charcuterie processes as meat.



The history of koji traces back to China. Early analyses of Neolithic pottery from the second millennium B.C. reveals residue of rice-based fermented wine. The first reference to using mold in culinary production comes from 300 B.C. in the time of the Zhou dynasty, and relates to the preparations of grain-based wines and bean pastes. Koji is a saccarifying mold, meaning that its most potent use is the breakdown of starches, which are heavily present in grains.

Over time, the fusion of koji with yeasts and ash (which was added to change the pH) isolated A. oryzae from other Aspergillus strains and non-related surface molds. This achieved two things: the wealth of variants in color and enzyme production within the species A. oryzae, and likely the mutation leading to koji becoming one of the only Aspergillus molds that doesn’t produce aflatoxins, which are toxic compounds produced by certain molds.






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