Koji - The culture behind Japanese food production
Koji - The culture behind Japanese food production
Koji is the culture behind Japanese food production, discover what it is and how it is used.

What is Koji?
Koji is not actually a yeast, as many people mistakenly believe. Koji is cooked rice and/or soya beans that have been inoculated with a fermentation culture, Aspergillus oryzae. This naturally occurring culture is particularly prevalent in Japan, where it is known as koji-kin, which explains why so many Japanese foods have been developed over the centuries using it. It is used to make popular foods like soya sauce, miso, mirin and sake.

The first step in making these products is creating the koji. This involves adding the Aspergillus culture to steamed rice or soya beans or, in the case of shoyu soya sauce, to a combination of steamed soya beans and roasted, cracked wheat. ?The resulting mixture is then placed in a warm and humid place for up to 50 hours, often in wooden trays called koji buta in Japanese. During this time the Aspergillus feeds on the rice or soya beans, using enzymes that are adept at breaking down carbohydrates and proteins.



How it is used?
Once it has been created, the koji is usually added to larger quantities of rice or soya beans, together with a brine solution. In the case of mirin, it is mixed with glutinous rice and the distilled alcoholic beverage shochu. In each case, the enzymes in the koji break down complex carbohydrates and proteins into amino acids, fatty acids and simple sugars. ?

When making sake, rice is mixed with koji, which breaks down the carbohydrates into sugars then subsequently fermented by yeast to produce alcohol and carbon dioxide.



The benefits of Koji
The amino acids, fatty acids and simple sugars released by the action of the koji add flavour, depth and, it has been argued, a number of health benefits to foods. For example, the fermentation of soya beans using koji to create miso is known to increase the levels of isoflavones (link to Q & A on isoflavones), which are compounds that are said to be effective in the prevention of cancer. 

One of the amino acids released by the action of koji is glutamate, which imparts an intensely satisfying and delicious savoury taste known as umami. This, combined with the simple sugars also released, ensure that foods made using koji have a uniquely rounded and deep flavour.

Fluffy white grains of rice koji, here being used to make sake.

Making koji for Clearspring's mirin.

Clumps of rice are broken up to ensure that the koji develops in a uniform way.

The rice inoculated with kojikin culture is placed in wooden trays in a warm, humid atmosphere to propagate.

Miso is just one of the many traditional Japanese foods that relies on koji...

...as is sake, here served in a traditional wooden container called a masu.

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About Miso & Koji
About Miso
Miso is a condiment peculiar to Japan, produced through fermentation of soybeans and rice. The prototype condiment of miso was brought from ancient China. Since then, Japan developed it into a unique fermented condiment for over 1,000 years. Miso is a precious source of nutrition, and, has always been an important food indispensable in Japanese dining of any era as a condiment for a soup to have with the staple food. The present merits of Japanese cuisine are widely acknowledged worldwide due to it having been registered as one of the world’s intangible cultural heritages, and miso is attracting attention as an extremely important condiment responsible for the “soup” in the traditional Japanese meal serving style “one soup and three side dishes”. About Miso
About Koji
Koji is steamed grains to which koji-mold (aspergillus) is inoculated and grown. When koji is made from rice it becomes “rice koji”, from barley “barley koji”, from soybeans “soybean koji”, and so on. Marukome uses “rice koji” for its miso products. Various enzymes are produced during the process of koji-mold growth on rice. These enzymes decompose starch in rice and proteins in soybeans, resulting in the delicious taste unique to miso.
Brewed condiments such as miso, soy sauce, sake, mirin and vinegar are the basis of Japanese cuisine, and they are not available without koji. It is no exaggeration to say that it is the “power of koji” that has sustained Japan’s unique food culture.
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Koji Making Process

Koji (a Japanese term for cultred grain) is made by inoculating steamed grain with the spores of Aspergillus oryzae, a mold that transforms the grain into sweet, fragrant koji, or cultured grain, during a two-day fermentation process. Making koji is the first step towards making miso. In Japan, rice koji is used for a number of other fermented foods beside miso, including sake, amasake, rice vinegar, and mirin.

Day 0
Certified organic grains are washed and soaked overnight.	
Day 1
	After the grain has been steamed by wood fire (about 45 minutes) it is removed from the cauldron, which is lined with a netted muslin sack for the steaming process.
	(left) Removing the steamed grain from the cauldron.
(line drawing to right) Removing the steamed grain from wooden steamer in the traditional Tsujita miso shop, near Tokyo, during the early 1970’s.


	The steamed grain cooling down in one of the two cooling boxes. The grain needs to cool down to 112ºF before it can be inoculated with the spores of the mold, Aspergillus oryzae.


	Spore powder of the mold, Aspergillus oryzae, is mixed with a small portion of the steamed grain (in this picture it is Barley). About 3 tablespoons of spore powder are used for 350 pounds of grain.
	Sowing the koji: This is a sacred moment in miso making, the beginning of the long journey of fermentation, which for some varieties may last as long as three years. The inoculated sample is sown evenly over the "field" of grain in the cooling box. This is the equivalent of the agricultural process of sowing grain on the earth. In this case, the grain itself becomes the "ground" upon which the koji is sown. It is an agricultural process raised up, above the earth, into a higher realm of life processes.

	Anni Elwell looking over cooking box filled with barley koji	
	The inoculated grain, now rightly called koji, is placed into a large wooden box lined with a muslin cloth. This box is called the "crib". The old masters recognized that the koji at this stage was like a newborn baby. This photo is from 1984. Christian with daughter, Anni, and, in his arms, Isaiah, about to transfer koji from the cooling boxes into the crib.	
	The koji will stay in the crib overnight. It goes into the crib at about 80ºF; by the next morning the temperature will be approaching 95ºF.

Day 2
	Morning of day 3: The koji is first stirred in the crib to oxygenate the growing mold while releasing carbon dioxide. Warmer and cooler areas of grain koji in the crib are mixed together. The grain is then removed from the crib and scooped by measured amounts into wooden trays. These "koji trays" are then stacked up in the koji room, a small incubation room heated to about 90ºF with high humidity.	

	
Koji trays stacked in first formation in koji room.
	Later in the day the koji is stirred in each tray to disperse the up-building heat from the intense metabolic growth of the mold. The trays are re-stacked in a more open, "brick-lap" formation to allow more oxygen to nourish the koji and prevent overheating. The warmth given off by the koji is sufficient now to maintain the heat in the room. The koji itself at this stage and for the night following will be at 90 to 100ºF.

	Trays stacked in koji room at end of day 2. (looking in from the production room).
Day 3
	On day 3 the koji is ready to harvest. By this time, about 48 hours after it was initially steamed and inoculated, the grain is covered with a fragrant bloom of white mold.

	
The mycelia of the mold bind the grains together into a solid mass. During its growth, the mold has created vast stores of digestive enzymes, which are crucial to the second part of the fermentation process, when the salted koji is mixed with the cooked beans.


The chunks of koji are broken up by passing them through a screen. The crumbled koji is then mixed with a carefully measured amount of sea salt. The amount of salt used depends on the variety of miso and the intended length of fermentation. The sea salt preserves the enzymes and food value of the koji, while preventing any further mold growth. Salted koji is now ready to mix with cooked beans.	
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https://www.youtube.com/watch?v=CC6TxqtMKS0

What is koji?/MISO
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