What is Nuruk?
Korean alcohol has three main ingredients; rice, water, and nuruk. Everyone knows rice and water but nuruk can still be a bit of a mystery to non-Korean speakers and this can lead to a bit of misunderstanding. It is important to fully understand this ingredient because it is one of the most important aspects of Korean alcohol.
In the most simple terms nuruk is crushed wheat that has been tightly packed into squares or circles then mold and yeast grow on it. Based on this nuruk may look simple but using different types of nuruk made in different locations can change the entire character of the resulting drink. It is one of the most important aspects of the brewing process and knowing it’s ins and outs is still something that is being studied.
Let’s start with how it is made. Most nuruk is made from wheat that has been crushed and packed into square or circular molds. It is then left in a high humidity environment for a week usually on a bed of straw or mugwort. During this time it will grow filamentous fungi, such as Aspergillus oryzae and Rhizopus oryzae and yeasts like Saccharomyces, Saccharomycopsis, and Pichia species. After seven days, the humidity of the fermentation chamber slowly decreases and the cake dries out. At this time the cake should be rather hard and compact and you shouldn’t see any mold on the outside. However if you break it open you will see a thin line of yellow that indicates the fungi have fully penetrated the nuruk. The middle should also be dry at this point. The final step is to break up the nuruk and dry it out.
Types of nuruk
Nuruk can be made with different types of ingredients. Most nuruk is made with wheat but it can also be made with rice and barley as well. Most nuruk manufactures will produce two different types of wheat nuruk one made with Korean wheat and another made with American wheat. Interestingly, this can lead to a big difference in the final taste of the alcohol. Typically, Korean wheat used for nuruk is called anjeung bengi wheat which is a shorter and higher in starch than its American counterpart. This leads to different fungal and bacterial profiles of the nuruk.
Wheat based nuruk isn’t the only type of nuruk. Another popular type of nuruk is eehwaguk (이화곡), or rice nuruk. Eehwagok is made from ground rice that has been formed into a ball slightly smaller than the size of a baseball. Eewhagok has the same fermentation process as nuruk but it is typically fermented on a bed of pine needles and will look a little different than wheat nuruk after fermentation. Eehwagok will start off white but can sometimes grow a dark green outer layer of mold. When it is broke open after drying it should be white and dry on the inside. Before being stored the moldy outer layer should be peeled off leaving a white ball that will be crushed into powder before brewing. Eehwagok is typically used to make a liquor called Eehwaju which has low water content and as a result is yogurt like in texture.
Both nuruk and eehwagok are a microcosm of many different types of fungi and microbes and as a result, the sugars, acids, and other compounds that they produce can vary wildly. This can have a large effect on the flavor of the liquor. While this might be a positive point to some, others prefer to have more consistency in the brewing process. So, some manufacturers prefer to use ipguk rather than nuruk. Ipguk is rice or wheat that has been inoculated with a single strain of fungus typically Aspergillus oryzae or Rhizopus oryzae. It is more similar to Japanese koji than to nuruk.
While embraced by some, it is sometimes seen as not as “traditional” to others. To these people it still carries some negative connotations with it and reminds them of the Japanese occupation period of the early 20th century. At that time home brewing was outlawed and village breweries were required to use ipguk rather than nuruk when making alcohol. Despite these connotations there are still some breweries that prefer to use ipguk over nuruk since it gives a more reliable result.
Of course, wheat and rice were not the only grains used to make nuruk. In the past there was a wide variety of nuruk made from different types of grains. These include nuruk made from black rice, brown rice, barely, millet, mungbean, sorghum, and more. Many of them have been lost to time but the Korean Food Research Institute (KFRI) has been doing research into some of these old style starters. They have been recreating different starters from old texts and seeing which ones make the best alcohol. They also isolate yeasts and molds from the nuruk to see what makes them different on a microbial level. They find the ones that work well in the lab then work with breweries to test out which strain of mold and yeast is the best to use for making alcohol. Their work is integral to Korean brewing and with their help will hopefully lead to its globalization.
Currently there is still so little information about nuruk in English it is easy to get misinformation about it. I hope this clears up what it is and how it works. If you want to know how to make it you can check out one of my previous posts on how to make nuruk. And if you have any questions about nuruk let me know.