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Food Science


Kimchi chemistry and cat-nose chromatography

by Krystal Vasquez
July 30, 2023 | A version of this story appeared in Volume 101, Issue 25


Flavorsome fermentation

A cross-section of a clay jar containing fermented cabbage.
Credit: Korean Ministry of Culture, Sports, and Tourism
Mysterious mechanisms: Kimchi fans have known that vegetables fermented in clay jars called onggis are higher quality. But until recently, researchers didn't know why.

Kimchi is such a staple in Korean cuisine that nearly 2 million metric tons of these spiced, fermented vegetables are consumed across South Korea annually, according to the Ministry of Agriculture, Food, and Rural Affairs of South Korea. Although the popular side dish was traditionally made using clay jars called onggis, most kimchi sold in South Korea today is mass fermented using glass, steel, or plastic containers.

But the food’s die-hard fans say that onggi-​fermented kimchi is far superior to versions fermented in modern vessels. They’re not being pretentious foodies either—science backs up these claims.

Previous research has found that an onggi’s kimchi is more acidic and has higher antioxidant activity than all other containers, says Soohwan Kim, a PhD student at the Georgia Institute of Technology. Onggis also promote the growth of lactic acid bacteria, the microbes that give kimchi its distinct sour taste (Int. J. Food Sci. Technol. 2011, DOI: 10.1111/j.1365-2621.2011.02710.x).

Some speculate that onggi kimchi’s superiority arises from the clay jars’ permeable walls, but no one had proved this scientifically. Kim sought to solve the onggi mystery with the help of his PhD adviser David Hu and Kim’s mother, who taught him how to make kimchi for his experiments. Kim outfitted an onggi with carbon dioxide sensors, added some plain, salted cabbage to the jar, and let the lactic acid bacteria do their thing.

Kim’s experiment, in combination with some fluid mechanical modeling, “showed that the onggi lets carbon dioxide out while the cabbage ferments,” he tells Newscripts. This gas exchange, aided by micropores across the onggi’s surface, mimics what happens in the loose soil that lactic acid bacteria naturally inhabit (J. R. Soc., Interface 2023, DOI: 10.1098/rsif.2023.0034).

In contrast, the CO2 levels were much higher in a glass container that Kim ran a similar experiment in. In these less permeable, modern containers, “lactic acid bacteria get suffocated by their own CO2,” Kim explains.

Modern fermentation methods attempt to accommodate for higher CO2 levels by “burping” their containers either manually or mechanically. The beauty of the onggi, Kim says, is that it achieves the same result without any outside intervention.

It’s unlikely that onggis will become mainstream again, as they’re quite expensive to make. Nevertheless, “it’s good to know about the science behind these old traditions,” Kim says.


Cat chromatography

The mouth and nose of a white-and-gray cat as it looks up.
Credit: Shutterstock
Supersniffers: Cat noses use a network of coiled tubes to differentiate between odor compounds, much like a gas chromatograph.

As sophisticated analytical instruments go, it’s tough to beat a cat’s nose. Cats’ sense of smell dictates a lot of their natural behaviors, says Kai Zhao, an otolaryngology professor at the Ohio State University. That’s why he and his colleagues whipped up an anatomically accurate model of a cat’s nasal cavity and simulated how air flows through it (PLOS Comput. Biol. 2023, DOI: 10.1371/journal.pcbi.1011119).

Using the model, Zhao and his team discovered that when a cat inhales, a portion of the air stream heads toward the lungs. The rest quickly makes its way to the feline’s olfactory system, where it is split among a network of coiled structures called turbinates. Each turbinate acts like a single gas chromatography column, detecting odor compounds as they interact with receptors positioned along the walls of the tubes.

Next, Zhao and his team plan to collaborate with neuroscientists to understand how the physical structures of cats’ noses help our furry friends perceive the world. Scientists can learn a thing or two from cats, Zhao tells Newscripts. Perhaps “we can learn from each other to build a better [gas chromatography] instrument.”

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