If you have ever cooked Japanese food with miso, soy sauce or mirin, you have already tasted the flavours that koji helps create, even if you have never bought koji itself.
Koji may sound like a specialist fermentation ingredient, but it is part of many everyday Japanese seasonings. Once you know what it is, Japanese pantry ingredients start to make more sense.
Koji is made by growing a beneficial mould on grains or beans, most commonly rice, barley or soybeans. In Japanese home cooking, rice koji is the type you are most likely to come across.
Koji is not usually used like a spice or herb that you sprinkle into a dish. It is used because its enzymes help break down starches and proteins in ingredients like rice and soybeans, bringing out sweetness, umami and depth.
You do not need to understand all the science to use koji at home. For everyday cooking, the important idea is simple: koji helps create flavour.
There are different kinds of koji depending on what the koji mould is grown on. Rice koji is made with rice and is often used for shio koji, amazake, sake and some types of miso. Barley koji is made with barley and is used for barley miso. Soybean koji is made with soybeans and is used in some miso and soy sauce making.
Shio koji is a salty rice-koji seasoning that is often used in everyday cooking. Amazake is a naturally sweet rice-koji drink that has long been enjoyed in Japan.
Koji is part of many everyday Japanese seasonings, including miso, soy sauce, mirin, sake, amazake, shio koji and shoyu koji. So even if koji feels new, the flavours it creates may already be familiar.
If you cook with miso, soy sauce or mirin, koji has probably been part of your cooking all along.
Koji helps create umami, gentle sweetness and depth. It makes miso taste richer, gives soy sauce its depth, and helps shio koji season and tenderise meat or fish.
Shio koji is a Japanese fermented seasoning made by mixing rice koji, salt and water. As it sits, the enzymes in koji help create gentle umami and sweetness. When used as a marinade, shio koji can help meat and fish become more tender, and it adds depth and roundness to everyday cooking.
For everyday home cooking, I think the easiest ways to use koji are shio koji (made with salt) and shoyu koji (made with soy sauce).
- Shio koji can be used as a seasoning or marinade for meat, fish and vegetables.
- Shoyu koji can be used like a richer, slightly sweeter soy sauce for tofu, eggs, rice or meat dishes.
If you are curious about koji, I would start with shio koji. You can make it with dried rice koji, salt and water, then use it as a marinade for chicken, pork, fish or vegetables.
Koji is originally made fresh, but the dried koji sold in stores is simply fresh koji that has been gently dried so it keeps much longer. A packet of dried rice koji is a practical starting point because it is shelf-stable and easy to measure.
With dried rice koji, you can make shio koji, shoyu koji and even homemade miso. Once you make shio koji, it becomes a small jar of seasoning you can keep in the fridge and use little by little. Homemade shio koji usually keeps for a few months in the fridge if stored in a clean container.
Koji may sound like a special ingredient, but it is already behind many familiar Japanese flavours. You do not need to start with a big fermentation project to understand it. Even a basic understanding of koji can help miso, soy sauce, mirin and shio koji make more sense.
Simple recipes made with shio koji can be surprisingly delicious, which is why I think it is such a good place to start.
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