When I introduce Soju to my non-Soju-knowing friends, their first question is often – “is it the same as sake?” My usual quick answer is “Sake is brewed like beer or wine but Soju is distilled like vodka or rum”. This usually pleases most people’s curiosities and we move on to drinking! But sometimes I get the opportunity to nerd out with the extra-interested. In these rare and precious moments, I like to talk about the difference between Korean Nuruk and Japanese Koji.
In both Korea and Japan, fermentation plays a crucial role in the production of traditional alcoholic beverages. Nuruk and Koji are fermentation starters integral to the production of alcoholic beverages in their respective cultures.
Koji is a type of mold that is used in the production of sake, also known as Japanese rice wine. It is made by inoculating cooked rice with the Aspergillus oryzae mold, which then grows on the surface of the rice. The koji mold secretes enzymes that convert the starches in the rice into sugars, which are then fermented to produce sake. The koji mold is carefully cultivated and managed to ensure that it produces the desired enzymes and flavors.
In Korea, a similar role is played by nuruk, a type of fermentation starter used in the production of Korean alcohol including takju (incl. makgeolli), yakju, cheongju, traditional soju, etc.. Nuruk is made by collecting and culturing the microorganisms that are found in the atmosphere of the brewer’s region. This is typically done by moistening a grain or flour (often wheat, rice, and barley) with water, shaping it into a large cake, and then allowing it to ferment naturally for 2-4 weeks in a heated room, without the addition of any specific mold or bacteria. The cake matures at a precise temperature until mold forms, resulting in a unique blend of microorganisms that reflect the local terroir and environment, showcasing the distinct cultural practices of Korea in alcohol production.
One key difference between nuruk and koji is their composition. While koji is produced using a specific type of mold, nuruk’s microorganism composition depends on the unique character of the local environment. For example, nuruk made in the Southern coastal region near Busan may have a higher composition of Lactic Acid bacteria compared to nuruk made in other areas (source: “Begin with Rice & Water: A Primer on Brewing Makgeolli” published by National Academy of Agricultural Science, Republic of Korea, GPRN 11-1390802-000946-01). This environmental variability makes the production of good nuruk notoriously difficult, requiring years of experience and a deep understanding of the brewer’s environment. Nuruk produces a large range of flavours and aromas including fruity, floral, earthy, and spicy notes. Depending on the region and the specific production method, the flavours and aromas of Korean alcohol that are made using nuruk can be very diverse.
This excerpt from “Begin with Rice & Water: A Primer on Brewing Makgeolli” provides a great example of the different methods and environmental impact on nuruk making:
“The exact compliment of molds, yeasts, and lactic acid bacteria in nuruk can depend upon the region where the nuruk was made. Also, different regions in Korea have unique methods of making nuruk that can affect the microbial content. For example, in the southern region surrounding Busan, nuruk is molded into a flat disk instead of the brick that is common to other regions. This difference in shape of the nuruk is to accommodate the warmer temperatures and humidity as well as prevent spoilage. As a result, nuruk made in the region surrounding Busan sometimes has a higher lactic acid bacteria content than nuruk made in other regions. Thus, the nuruk’s terroir, or region of origin, can have an even more profound effect upon the final character of the brew than the region of the rice.”
Overall, nuruk and koji are similar in that they are both used as ferment starters in the production of Korean and Japanese alcohol, respectively. However, they are different in their composition, the way they are made, and the flavors and aromas they contribute to the finished product. These differences reflect the unique cultural and production traditions of Korea and Japan.