By Wonsuh Song
Kimchi, Korea’s most iconic fermented food, is loved by many—but how many of us truly understand how it is made and what drives its fermentation? The key lies not just in the salted napa cabbage but in the invisible world of microbes.
As a geographer who once studied microbiology in graduate school, I first became fascinated with the way microorganisms weather rocks. That scientific curiosity eventually led me to explore the microbes behind traditional fermented foods, including kimchi. What I found was that kimchi’s soul rests in one unassuming ingredient: jeotgal—fermented fish sauce.
Jeotgal is not merely a seasoning. It is the microbial heart of kimchi. Whether it’s saeujeot (salted shrimp), anchovy extract, or kanari fish sauce, these fermented condiments are already teeming with salt-tolerant microbes like lactic acid bacteria and proteolytic bacteria. When added to kimchi, they become the engines that drive its fermentation.
Kimchi made without jeotgal tends to spoil or develop off-flavors. That’s because it lacks the right microbial population—what ends up taking over are wild, uncontrolled bacteria. Jeotgal ensures not just proper fermentation but the complex umami and aroma that define authentic kimchi.
But microbes don’t work alone. They need fuel. In jeotgal, fish proteins provided that nourishment. In kimchi, we often add pul, a porridge made of rice or wheat flour, to serve as an energy source. This ‘gruel’ gives microbes the sugars and nutrients they need to multiply rapidly.
That’s also why we leave freshly made kimchi out at room temperature for a day or two before refrigerating it. In this warm environment, microbial populations double quickly, jump-starting the fermentation. Once this happens, cold storage slows the process and allows flavors to develop over time.
Even additions like grated apple, pear, or oysters serve a microbial function: they are all nutrient-rich ingredients that influence flavor and fermentation speed.
Ultimately, kimchi is the result of a delicate collaboration between nature and human know-how. Understanding its fermentation mechanism enriches not only our appreciation but also the pride we take in this culinary heritage. It’s time we start enjoying kimchi not just with our taste buds, but also with our scientific curiosity.
Wonsuh Song (Ph.D.)
Full-time Lecturer, Shumei University / NKNGO Forum Representative
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