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The secret of UMAMI in soy sauce: How Koikuchi soy sauce is produced!

The soy sauce's umami is produced as the various types of amino acids are changed by the koji mold (Aspergillus oryzae) during the fermentation and brewing process. Glutamic acid is the main component of soy sauce's umami.

No matter how large the automated plant is, soy sauce is produced through the traditional process of fermentation and brewing to produce umami.

Here is how standard soy sauce (Koikuchi soy sauce) is produced: 


The basic ingredients of soy sauce are soybeans, wheat and salt.

First, the soybeans are steamed and the wheat is roasted and crushed.

Heat treatment enables the koji mold to easily propagate and for its enzymes to react with the proteins in the soy beans and the starch in the wheat.

For standard soy sauce (Koikuchi soy sauce), the soybeans and wheat are mixed at a ratio of 1:1.

Koji mold spores (green Aspergillus oryzae or Aspergillus soyae) are sprinkled on the soy bean and wheat mixture and left to germinate for about three days to create soy sauce koji in a room called muro where the heat and humidity are carefully controlled.

Koji mold creates enzymes and these enzymes help to change the proteins in soy beans to amino acids and the starch in wheat to glucose. This is the first secret of umami!


Next is the time for salt, one of the most important ingredients in soy sauce.  Salt protects the activity of the microorganisms from bacteria because of its high concentration of salinity.

Salt water is blended with the soy sauce koji mold produced in step 1. The ratio of salt water to soy sauce koji mold is generally 11-13:1. This mixture is called moromi.

At first we can see the shape of the soybeans and wheat in the moromi. The manufacturers or artisans put this moromi in their tanks or kioke (wooden barrels) for fermentation and brewing. 



It takes at anywhere from 6 months to 3 years for the fermentation and brewing. During this period, the artisans stir the moromi at certain intervals to keep the best environment for the activity of the microorganisms.  

In automated factories, soy sauce is brewed in temperature-controlled tanks and stirred at certain intervals.  This enables them to provide soy sauce to the market at a stable price. Here too, the umami is added to the soy sauce by the natural power of microorganisms.

For artisans or manufacturers using kioke (less than 1% of all manufacturers), stirring the moromi at certain intervals is quite difficult, especially in the summer or winter. However, by using kioke the microorganisms, the heroes of the fermentation, that live inside the kioke barrels will create an ecosystem unique to that brewery (please see more details in Kioke here).

In this way the fermentation and brewing are the key secrets of soy sauce umami!


Raw soy sauce is pressed from the moromi by weights and the brewed thick moromi is then wrapped in cloth and set in layers. The process differs slightly depending on the manufacturer or artisan but is basically the same.

Artisan manufacturer:            Large factory:


The raw soy sauce is then heated. This stops the activity of the enzymes and adds a special fragrance to the soy sauce (reminiscent of the scent of a BBQ). The heating time depends on the manufacturer, such as at 80 to 85°C (176 to 185 °F) for 10 to 30 minutes, or a lower temperature (65°C, 149 °F) for a longer time. 

After a quality check, the bottled soy sauce can be put on the market.


Go to Koikuchi Collection 

Refer to process of Tamari soy sauce 

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