Staff Writer
Kimchi, a fiery, pungent Korean meal made from fermented cabbage, has been made for more than a thousand years in clay containers called “onggi.” Now, a pair of mechanical engineers have figured out why these vintage Tupperware, which were formerly made of mud pounded and slapped by hand and spun on a pottery wheel, are well suited to encouraging the growth of probiotic microorganisms that turn ordinary cabbage into a gourmet superstar.
Due in part to the gut-healthy bacteria that contribute to kimchi’s unique punch and sour flavor, kimchi has gained popularity as a superfood. Onggi, however, have not done so, probably as a result of their thickness, weight, and fragility and the fact that they were not truly intended to be portable or fit onto contemporary kitchen worktops. Many Koreans fill a second, specialized refrigerator with contemporary glass, steel, or plastic containers of kimchi instead of utilizing onggi that are buried in the earth.
According to earlier research, kimchi made in onggi contains higher levels of lactic acid bacteria, antioxidant activity, and acidity, as well as a slower rate of growth for bad-tasting bacteria. Yet why?
David Hu, a mechanical engineer at Georgia Institute of Technology who previously explained the “wok tossing kinematics” of preparing fried rice, stated, “I thought there’s still a big missing link.” “Everyone thought pores were significant. People didn’t know why kimchi grown in these conditions had more [lactic acid] bacteria.
The results of the new study, which were published in the Journal of the Royal Society Interface, show that onggi’s walls are covered in teeny-tiny micro-pores. It is possible for salty water to pass through and evaporate, creating “salt flowers” on the object’s exterior. Additionally, because of the holes, the pottery can exhale some of the carbon dioxide produced during fermentation, which fosters the growth of lactic acid bacteria.
The advantages of employing an onggi are intuitively understood by many skilled chefs. Maangchi, a popular Korean chef on social media, claimed to have numerous onggi that she used to make a variety of foods, including gochujang (fermented hot pepper paste), doenjang (fermented soybean paste), and jangajji (salty Korean fermented pickles).
She keeps more than a dozen of the enormous pottery pieces in the window of her New York City apartment so they can catch the sunlight. Her apartment has large windows. She recalls that her grandmothers maintained the exteriors of their onggi very clean, possibly because they knew that the pots required air to breathe even without having access to precise scientific measurements.
A mechanical engineer at Georgia Tech named Soohwan Kim oversaw the trials with assistance from his mother, whom he refers to as his “kimchi mentor,” and stated the goal of the research was to understand how those pores function using the field of fluid mechanics.
On the volcanic island of Jeju-do in South Korea, where onggi are still made today, Kim spent his formative years. He returned home to conduct the majority of the research and purchase an onggi. He focused on the pores and measured them using a scanning electron microscope and a CT scan. These measurements enabled Kim and Hu to build models to comprehend the intricate fluid mechanics involved in the production of kimchi.
In order to conduct studies that would allow them to quantify the levels of carbon dioxide, oxygen, and pressure inside the onggi in order to better understand how it breathed, the scientists prepared a standardized and de-spiced version of salted cabbage. They discovered that the vessel produced an environment that was favorable for the growth of probiotic bacteria even without the use of specific valves, sensors, or monitors.
According to Maangchi, she once made two batches of kimchi—one in an onggi and the other in a jar stored in the refrigerator—as a taste test. She organized a tasting in Bryant Park for her readers to sample the two varieties.
She claimed that they generally couldn’t tell the difference.
Onggi are made from local clay by Hayun Surl, an assistant professor of ceramics at Angelo State University in San Angelo, Texas. Onggi is still used in cooking by a lot of people, he acknowledged, but onggi is also evolving from a strictly functional item into a work of art with cultural and symbolic importance.
To be honest, the kimchi from the kimchi fridge isn’t that horrible, Surl said. “We want to save space because most apartment dwellers don’t have a yard where they can store the large onggi jars,”
Star New York chef Eunjo Park claimed that there isn’t room for onggi in her compact residence. She claimed that other family members who reside in the suburbs have kimchi refrigerators, which assist maintain a more consistent temperature. Although Park acknowledged that contemporary tools can be used to manufacture kimchi, she still treasures the memory of eating her grandmother’s kimchi from a buried onggi, which had a distinctive fizz.
“It becomes really poppies with the [lactic acid bacteria] fermentation, similar with soda. That is built,” stated Park. “Regular kimchi you try to buy in a store is sour and lacks the pop.”
