What is Koji?

Koji is the key ingredient for various traditional Japanese fermented foods such as soy sauce, Miso, Mirin (rice wine), rice vinegar, and Sake. These staple ingredients for Japanese cooking and diet are all fermented by a type of traditional rice culture called Koji culture (fungi: Aspergillus oryzae). It usually looks like grains covered by mold. The colour could be white, yellow, or green depending on what type of Koji. For making the Japanese staple ingredients mentioned above, white rice Koji is the most commonly used type. However, various types of grains and soybeans can be inoculated by Koji culture to make different types of Koji.

Where Koji came from?

There are several different opinions as to where Koji culture originally came from, but the use of Koji was most likely introduced from China, like many other Japanese food culture. It is believed that the Koji fungi widely used now in Japan was harvested from the mold on the ears of rice grown in Japan. Over time, the Koji fungi was refined enough to established monopolies of “Koji culture”, and became a commodity by the 17th century.

Recently, Koji culture was researched more closely and categorised in detail by The Scientific Conference of Brewing Society Japan , and in 2006 they claimed Koji fungi as Japanese National Culture.


How Koji is made?

Ingredient-wise, all you need is two ingredients, Koji culture (Aspergillus oryzae) and a medium to inoculate the culture. The types of Koji are determined by the medium. The most common medium widely used for Koji production in Japan is medium grain white rice. Despite the simple ingredients, the process of making Koji is quite complex. In short, it is all about creating the optimum environment for the culture to work. It takes about three days from the preparation stage to the end of the production process.

Firstly, the medium needs to be rehydrated and steamed so that the culture can start acting on the nutritional elements within the medium. Koji culture needs to be evenly seeded over the cooled medium. The next step is to keep the medium in a controlled environment in terms of the temperature and humidity. If the medium is kept in an optimum environment, it should start heating within 24 hours, and it should usually be ready to be used within about 40 hours all up.

What role Koji plays in cooking?

In the last five years, it appears chefs in the fine dining scene (especially in Europe and the U.S.) have been attracted to Koji, and the trend seems to have arrived in Australia a couple of years ago. The secret of Koji is in the uniqueness of its enzyme varieties. Creating a strong Umami flavour and softening ingredients would be two of the most distinctive functions of Koji, but it all depends on which characteristics of Koji you wish to utilise.

Normally, concentrated Umami can be found in ingredients which have a strong flavour, and that have a certain texture such as mushrooms or meat. Whereas Koji itself is quite neutral in flavor and flexible in format. These characteristics makes Koji as a powerful and special Umami source. It can be used for anything from sweets to mains and drinks, and it becomes an especially powerful tool for vegetarian/vegan dishes because a full body flavor can be achieved without any animal oriented Umami.

Koji can be used in its original grain format, but also could be used in a powder, paste or liquid format. Koji can be added at any stage of the cooking process from preparation to the garnishing stage. It can act as a salt alternative, a sweetener, flavour enhancement, or as additional texture to dishes. Koji also contains valuable vitamins as well as essential amino acids and digestive enzymes. When it is used in the preparation stage, it helps human bodies absorb nutrients.

What is the logic behind Koji’s characteristics?

The three main enzymes contained in Koji are amylase, protease, and lipase. These enzymes break down the nutrition in food and it transforms the original nutritional elements such as carbohydrate, protein, and fat into more accessible (easy to absorb) elements such as amino acids (the source of Umami), and glucose (sweetener). This breakdown process also means that adding Koji to food achieves a softening of the ingredients.

How to use different format of Koji?

There are several options available.

① Salty (Shio) Koji, ② Tamari Koji, ③ Spicy Koji, ④ Amazake, and ⑤ Straight Koji.

1. Salty Koji

Salty Koji is an alternative to salt, but in a runny paste form. It tastes a lot milder and sweeter than normal salt because of the strong Umami element. Salty Koji helps in highlighting the original flavour within ingredients by extracting sweetness and Umami elements naturally in them. So, the effect of salty Koji resembles MSG, but it’s not “adding” any artificial element but instead just extracting the existing natural flavour in the ingredients itself. Salty Koji is made from simple ingredients: Koji, sea salt, and water. It can be used to replace salt in any dish, or even in sweets and drinks.

How to experience the effects of Salty Koji?

Simply chop up some fresh vegetables suitable for a stir-fry (such as broccoli, green beans, and cauliflower etc.), put them in a bowl, coat them by a little bit of oil and add some Salty Koji next (just lightly coat the surface). Set it aside for a few minutes, then stir-fry them in the usual way and compare the difference in flavour. The starchy texture of Salty Koji will also aid emulsifying the marinade to avoid ingredients becoming too watery.

2. Tamari Koji

Tamari Koji is a marinated Koji in Tamari sauce. If you have normal Tamari in your kitchen, just taste test some of it and compare to Tamari Koji. You would immediately notice the difference in depth and complexity of the flavour and some pleasant sweetness in the Tamari Koji. Tamari Koji is good for baking dishes or BBQs because of the rice grains from the Koji. They will become caramelize and provide extra texture and bursting aroma.

3. Spicy Koji

This is a spicy version of Salty Koji. It is quite a strong flavour which contains saltiness, spiciness, but also sweetness. The texture of Spicy Koji is a lot stickier than Salty Koji, and it is very concentrated.

The basic use of Spicy Koji can be similar to Salty Koji, but because of its spiciness, it is best to be used for the base of a spicy Asian dishes such as a curry or even in Mexican or Italian style dishes. It’s a good combination with creamy ingredients such as thick cream, sour cream, cream cheese, coconut cream, silken tofu, and so on…

4. Amazake

Amazake is a sweet creamy rice paste, and is white in colour. It has a subtle honey or malt like fragrance. It is used as a sweetener, with a thickener effect added. During the fermentation process, Koji breaks down the carbohydrates in rice to glucose, then it becomes extremely sweet. It takes about 10 hours to make, and its transformation process is quite amazing.

The simplest use of Amazake is using it as a straight paste, as a creamy topping for desserts, and also it will make a nice thick drink such as a smoothie, by combining with milk and/or fruit. Another way of using it is to make a sake cocktail. Because it is made from the same original ingredients, Sake and Amazake are a great combination.

It is called Sake (Zake) because it is made from the same ingredients as Sake (alcohol), but it actually is non-alcoholic. Also it is named Sake (Zake) because Amazake is made by Sake brewers as a side product during their off season.

Nutrition-wise it is full of vitamins. Normally, vitamins in supplements cannot be fully absorbed by the body because it’s not in its natural form, whereas absorption ratio of the natural vitamins in Amazake is around 90%. Also, the Vitamin B2 level is increased by 6.3 times as much from the original ingredients because of the chemical transformation in the fermentation process.

5. Straight Koji

Straight Koji is in grain format, but it’s texture can be quite different depending on the type of Koji. Each Koji has significantly different aroma and texture. Some chefs use straight Koji by roasting and grinding to add texture to the dish. Others use it by soaking them in milk to transform its flavour to the liquid.

Here are some examples of unique Koji. Buckwheat Koji, Rye Koji, Spelt Koji, Amaranthus Koji, and Quinoa Koji. Even Teff (Ethiopian grain) can become Koji.