What Is Koji?
The Japanese food culture owes a lot to a microscopic organism called Aspergillus oryzae, also known as koji-kin. The action of this magical mould, which grows on a variety of grains, is crucial to the production processes that result in soy sauce, rice vinegar, and miso. Traditionally these are Japanese seasonings that are used in much of their cooking. As an essential ingredient of sake, koji-kin is also used as part of rice and water, a use which dates back to the Nara period (710-94).
As of 2006, the Brewing Society of Japan officially named koji-kin the "national fungus" of Japan.
Koji-kin is the key element necessary to make sake. It is what turns rice starch, with no fermentable sugars, into sweet koji rice suitable for alcoholic fermentation.
The process of turning starch into glucose (sugar) is called saccharification.
There are three different types of koji-kin, or koji mould, all delineated by the colour of their spores.
Scientifically called "aspergillus oryzae" in English, yellow koji is used to produce sake, soy sauce and miso. Yellow koji produces potent enzymes to saccharify starch and break down proteins.
"Aspergillus awamori" in English is used in Awamori production, a distilled spirit unique to the tropical islands of Okinawa. Black koji's distinctive characteristic is its high production of citric acid and enzymes to saccharify starch.
Scientifically known as "aspergillus Kawachi", it is a mutant form of black koji, and it is mainly used in the production of shochu, Japan's national distilled spirit.
Shochu producers also offer yellow koji versions of their products, which offer more citrusy and fruity aromas. Consequently, rice-based shochu produced with yellow koji has a more sake-like taste.
Koji & Sake.
When talking about koji and sake, it is critical not to confuse koji-kin, the fungus, with rice koji. Rice koji is steamed rice onto which the koji-kin mould has been cultivated.
Rice koji is crucial to sake brewing. The rice koji is usually made by hand at breweries, but machines can also be used to create it. Sake makers often use this saying to describe the importance of rice koji production: "First comes the koji, then comes the moto and then comes the fermentation."
Rice koji is made in a dedicated room called "koji-muro". It is because temperature control is crucial to the production process. Throughout the entire 48 hour process, the temperature needs to be above 35C (95F). Firstly, steamed rice is put into the koji-muro. The koji mould is sprinkled on top after cooling the rice a bit. Rice is then mixed frequently and checked to maintain a constant temperature and humidity level throughout the 48-hour process.
It is a sweaty and challenging process that will significantly influence the final flavour of the sake.
There are two types of rice koji—each with its distinguishing characteristics leading to the brewing of different types of sake. They are classified based on how the koji mould propagates onto the rice.
The first type of rice koji is called "souhaze-gata", which is the most aggressive type as the fungus covers the entire surface of the rice kernel and penetrates deep into its centre. This kind of rice koji creates full-bodied sake with more intense flavours (think junmai).
Rice onto which Koji-kin has been cultivated
The second type is called "tsukihaze-gata" where the koji mould still bores its way to the core of the kernel but only sparsely covers its surface. This type of rice koji leads to more delicate, smoother and lighter sakes with subtle fragrances (think ginjo and daiginjo).
The use of koji mould is what makes sake unique and sets it apart from wine, beer and other fermented beverages.
We believe the future of sake lies within koji innovation, with the takeover of breweries by the younger generation and the international expansion of the market. Just as with the craft beer movement, experimentation will lead to new discoveries and the emergence of distinct flavours, aromas and styles of sake.
It is an exciting time for the category, so make sure to keep an eye open for the arrivals of the latest brews from innovative breweries bridging tradition and savoir-faire with new technologies and experimentations.