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ICHIZEN Japan Restaurant

Koji (麹)


Koji (麹) is a microorganism used in the production of traditional fermented foods and seasonings in Japan. Koji is mainly made from rice and soybeans, but it can also be made from other grains and legumes.

What is Koji?

The primary component of koji is produced by a group of microorganisms known as koji-kin, with the most common species being Aspergillus oryzae. Although other microorganisms can be used, Aspergillus oryzae is the most common.

Koji has a wide range of applications and can enhance the flavor of dishes. It is used in many elements of Japanese and Asian cuisine. Soy sauce is made by fermenting soybeans, wheat, salt, water, and koji. Miso soup, a familiar dish at ICHIZEN, also uses koji. Miso is made by fermenting soybeans, salt, and koji. Koji is also used in the essential mirin, a seasoning in Japanese cuisine. Additionally, the health benefits attributed to Japanese sake are in part due to the power of koji.

The Making of Koji

To make koji, koji-kin needs to be cultivated at the right temperature and humidity. Koji-kin is cultured in a special environment called a koji bed. In the koji bed, grains (primarily rice or soybeans) are mixed with koji-kin and left to ferment for a specific period under controlled humidity and temperature conditions. During this process, koji-kin produces enzymes that break down starches and proteins in the grains, resulting in various chemical changes. The unique fermentation process and microbiological characteristics give rise to flavors and umami, adding depth and richness to foods.

Koji and Beauty

Koji is believed to have several benefits for beauty.


Koji is rich in nutrients beneficial for beauty, including vitamins, minerals, amino acids, and more. These nutrients support skin health and can improve skin brightness and elasticity. Koji's lactobacilli may also improve gut health, which can, in turn, impact skin condition, as a healthy gut is crucial for maintaining beautiful skin.

Koji contains abundant antioxidants, which can protect the skin from external environmental factors such as UV radiation and stress. Antioxidants help neutralize harmful molecules known as free radicals, potentially reducing the signs of wrinkles and aging.

Supplying Biotin

Have you heard of biotin? Koji is rich in biotin (also known as vitamin H or B7). Biotin is an essential vitamin for skin, hair, and nail health, contributing to the improvement of these aspects.

Primarily used as a fermented food, koji is part of the fermented foods category. It may improve gut health and have an impact on beauty. A healthy gut environment is known to contribute to beautiful skin.

Koji and Health

Koji (こうじ) is believed to offer various benefits for health and is widely used in traditional Japanese cuisine and fermented foods.

Koji is a fermented food that supplies beneficial probiotics to the gut. These probiotics improve the gut environment, promote the growth of beneficial bacteria, and contribute to overall health. It is also rich in nutrients, including vitamins, minerals, amino acids, and enzymes. These nutrients are essential for the body, with notable inclusions such as the B-vitamin group (B1, B2, B3, B6, B12), biotin, folic acid, and iron.

Koji is considered a low glycemic index (GI) food, which means it can help stabilize blood sugar levels and support diabetes and weight management. Low GI foods provide energy over an extended period and sustain a feeling of fullness.

The dietary fiber and fermented products found in koji may contribute to improved cholesterol levels. Specifically, condiments and foods made from soy koji are believed to help lower cholesterol levels.

Koji is rich in antioxidants, which can neutralize free radicals in the body, protecting cells and tissues from oxidative stress. This may contribute to the prevention of aging and chronic diseases.

SHIO Koji (Salt Koji)Recipe

Salt koji is a versatile ingredient that can be used for marinating meats or fish, as a seasoning in stir-fries, or as a base for dressings. Here's how to make it:


Rice koji: 1 cup

Salt: 1/4 cup

Water: 1/4 cup


Wash the rice koji to remove impurities, ensuring that it is not soaked in water.

In a bowl, combine the washed rice koji and salt, mixing well to evenly distribute the salt.

Gradually add 1/4 cup of water, mixing to form a paste. Adjust the water as needed for your desired consistency.

Transfer the mixture to a clean glass jar or plastic container with a tight-fitting lid.

Seal the container and let it ferment at room temperature for about 1 to 10 days. You can promote even fermentation by shaking or stirring the mixture during this period.

After 1 to 10 days, your salt koji will be ready. It will become thicker as fermentation progresses. Store it in the refrigerator once it reaches your desired consistency.

Salt koji can be used for marinating meats or fish, in stir-fry dishes, or as a dressing base. It adds depth and flavor to your cooking.

At ICHIZEN, we offer a miso soup as part of our lunch set menu. We believe that a balanced diet contributes to improved well-being and productivity in your afternoon work.

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