The process of making miso paste starts with the production of a product known as koji. Koji is a Japanese term used for describing mold grown on rice, barley or soybean. There are several strains of koji spores used in different industries (miso, soy sauce, sake brewing, etc.).
The production of koji requires two types of ingredients: grains (rice or barley) and spores (A. oryzae). Historically, wild spores were attracted by using natural materials (e.g. hay) to endure the process of incubation in warm and humid conditions. With the advancements of science and technology, the spores were successfully domesticated and isolated from another type of spores from the same family, Aspergillus flavus.
Apart from Aspergillus Oryzae, dedicated mainly for miso production, the producers of other ferments, such as sake or soy sauce, use different types of spores from the Aspergillus family.
Most popular ingredient for koji is rice. It has a sweet or semi-sweet smell and taste with notes of chestnut and apricot. Due to high concentration of sugars, it is a great medium for building white miso or sake. The latter application is interesting due to its dual parallel fermentation processes (break down of starches by enzymes and simultaneous conversion of sugars into alcohol by yeast). Rice koji is usually inoculated with A. oryzae or A. luchuensis.
Second popular choice for growing koji is a different type of grain – barley. Most popular in Japan in 10th century (due to high price of rice back then), it is now a common choice in Western countries (especially Denmark) due to more earthy notes and distinctive mushroom taste. Barley koji is also semi-sweet with full-bodied flavor. It is what companies like Empirical Spirits or restaurant Noma choose as their go-to fermenting agent in production of innovative products.
Soybean koji is another type of ingredient, that could state its own category in koji world. Mixed with wheat kernels and inoculated with Aspergillus soyae, it is the main product in production of world renowned soy sauce. Koji brown on soybean with A. oryzae, later mixed with cooked soybeans lead to production of hatcho miso – deep and rich, long-fermented miso paste.
Other types of koji
Some of the pioneers of modern fermentation and koji-making push the boundaries and reformulate the understanding behind the traditional techniques. Jeremy Umansky from the restaurant Larder in Cleveland, Ohio (United States of America) has been experimenting with these applications for many years and has proven that the technique of koji making can be applied to substrates other than rice or barley (e.g. popcorn, buckwheat, cacao nibs). This allowed him to create unprecedented food items and look at traditional Japanese fermentation techniques from a new perspective. Additionally, he standardized the process of making vegetable charcuterie and koji-curing meat cuts