People often ask, what makes soju different from other rice distillations? How would you distinguish it from, say, Japanese shochu?
Depending on who’s answering, the explanation could take up the rest of your afternoon with all its complexities. However, there is one fundamental difference that makes traditional soju stand apart from other rice alcohols, and that is the use of nuruk.
Difference between Korean and Japanese styles
Nuruk is the fermentation starter that creates the base alcohol which distills into soju. The Japanese method uses both koji to convert rice to sugar and yeast to convert sugar to alcohol. Nuruk does both jobs in one simultaneous process.
How to make a nuruk cake
Nuruk in itself ferments at much warmer temperatures than alcohol. This was traditionally done in the summer months when brewing was difficult. What constitutes nuruk varies, cultivating on starches such as rice flour, mung beans and wheat flour. The most common ingredient these days is whole ground wheat.
The ground wheat mixes with just enough water so that forms a cohesive shape. The brewer then then packs into a frame lined with cloth and steps on it using her heel to get enough pressure to pack it in tight. After stepping on the wheat cake long enough so that it doesn’t fall apart, she carefully pops it out of the frame and places it in a space that maintains temperatures between 26 and 37 degrees Celsius (~79 and 99 degrees Fahrenheit).
During the nuruk fermentation process, molds, yeast and bacteria inoculate the cake, and as moisture slowly releases, the cake becomes hard as a rock. If you’ve done a good job, you can then be crack the cake open and smash it into little pieces for curing in the sun, removing any musty, moldy aromas.
How to use nuruk
After all that hard work, the enzymes in the nuruk change the rice into sugar and the yeast converts the sugar into alcohol. This creates a complex and aromatic sool. Drinkable on its own as a strong wonju, allowed to sit and separate into a cheongju layer, or watered down for a lighter makgeolli, it’s up to the drinker to decide. If you spoon off the cheongju and distill it using a pot or reflux still, you can achieve a sweet and floral soju with a slightly earthy aroma.
While many sojus of today use a variety of ingredients and techniques, it’s safe to say that the truest expression of traditional hand-crafted soju comes from Korea’s unique fermentation starter, nuruk.