Discovering Shio Koji

The fermenting fungus that wound up in everything
Culinary World Mar 05, 2021 Chelsea van Hooven
Shio koji fermentation

The first sources documenting the domestication of Kōji (Aspergillus oryzae) are from the year 300 BC. This mold was found in China and began to spread throughout the Asian region. In Japan, the culture of fermenting with Kōji has found significant importance and has become a substantial part of the culinary scene as it is used to make the most traditional products such as sake, mirin, rice vinegar, soy sauce, and miso. It is also used extensively in China and Korea to ferment and mature various foods.

The rice fermented with the fungus Aspergillus oryzae is called "Shio Koji" in Japanese and has been used in cooking for centuries as ahealthy alternative to salt and soy sauce, It is similar to the use of bacteria and yeast that give character to our Western cuisine to make cheese, beer, and wine. The difference is in the type of fungus used in the fermentation process.

Shio koji fermentation1

So how does the mold come to life?

First of all, it requires a substrate on which it can grow (this works particularly well on cereals such as buckwheat or rice). The spores of these mushrooms are mixed into steamed rice and then develop at a temperature of about 50° degrees and humidity around 80 percent - comparable to the conditions such as those found in the climates of Japan and China. The process takes about 48 hours to be completed, and in the end, the grain is covered with its white moldy coat.

During the growth process, the enzymes of koji break down the starch and protein in the grain, transforming the starch of the rice into sugar and realizing a series of fatty acids and amino acids, - within them, glutamate, the basis of the "fifth taste". Yes, UMAMI! This mixture is called "kome-kōji" in Japan. Once the mixture is enriched with a little sea salt during further processing, "shio kōji" is created. After adding salt, the resulting “umami salt” develops in a few days at room temperature. This process allows the sugars, but not the amino acids, to develop further. So the paste has now become an umami bomb. The sugar and salt content brings out the umami flavors of the products. This incredible flavor enhancer can be used on basically anything. Anything from fish to meat, tofu, and vegetables can be marinated with it.


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