Koji Yeast

Koji Yeast is a fermenting aid used in China and Japan in creating products such as miso sauce, soy sauce, sake, shochu, huangjiu, natto, etc.

It is a mould with long, dark green spores [1]. The mould creates enzymes which in turn convert long starch molecules in food items such as rice, potatoes and grain into small sugar molecules such as glucose for other yeast to feed on. Other sugars are produced that yeast can't use, but those other sugars are important anyway in carrying through a flavour to the finished product.

The propagation of Koji is called "seigiku." It is done in breweries in a room called a "koji muro."

Generally, the base food item is husked rice, or husked rice and barley. The rice or barley is steamed first to cook them, then is sprinkled with the mould spores. The spores are allowed to work 40 to 45 hours at a controlled temperature to encourage spore activity.

The process is mostly done by machine now, though Koji for the most expensive sakes is still made by hand.

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[1] A separate species, "Monascus purpureus" is red. The fermentation process is generally not allowed to exceed a three day period, both because of the desired results, and because some mycotoxins could be produced, such as Kojic acid, Maltoryzine, Cyclopiazonic acid and b-nitropropionic acid.
Koji is not really found in nature. It is presumed to have evolved through years of selection in cultivation from a mould called "Aspergillus flavus." It's presumed that Koji can only survive for a short time in the wild.

Koji has been used since around 1,000 AD in Japan.

It was sold as commercially as "Takadiastase" by a Dr. J. Takamine in Clifton, New Jersey starting in 1894.

Also called:

Shochu

Active Dry Yeast, Bread Machine Yeast, Brewer's Yeast, Compressed Yeast, Cream Yeast, Fast Action Bread Yeast, Fresh Yeast, Inactive Yeast, Instant Yeast, Koji Yeast, Torula Yeast

Chemical Leaveners, Starters