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hubie [soylentnews.org] writes:

Want Better Kimchi? Make It Like the Ancients Did [gatech.edu]:

Fermented foods like kimchi have been an integral part of Korean cuisine for thousands of years. Since ancient times, Korean chefs have used onggi — traditional handmade clay jars — to ferment kimchi. Today, most kimchi is made through mass fermentation in glass, steel, or plastic containers, but it has long been claimed that the highest quality kimchi is fermented in onggi.

Kimchi purists now have scientific validation, thanks to recent research from David Hu [gatech.edu], professor in the George W. Woodruff School of Mechanical Engineering [gatech.edu] and the School of Biological Sciences [gatech.edu] at Georgia Tech, and Soohwan Kim, a second-year Ph.D. student in Hu's lab.

In a combined experimental and theoretical study [royalsocietypublishing.org], Hu and Kim measured carbon dioxide levels in onggi during kimchi fermentation and developed a mathematical model to show how the gas was generated and moved through the onggi's porous walls. By bringing the study of fluid mechanics to bear on an ancient technology, their research highlights the work of artisans and provides the missing link for how the traditional earthenware allows for high quality kimchi.

[...] "We wanted to find the 'secret sauce' for how onggi make kimchi taste so good," Hu said. "So, we measured how the gases evolved while kimchi fermented inside the onggi — something no one had done before."

The porous structure of these earthenware vessels mimics the loose soil where lactic acid bacteria — known for their healthy probiotic nature — are found. While previous studies have shown that kimchi fermented in onggi has more lactic acid bacteria, no one knew exactly how the phenomenon is connected to the unique material properties of the container.

[...] They concluded that the onggi's porous walls permitted the carbon dioxide to escape the container, which accelerated the speed of fermentation. The onggi's porosity also functioned as a "safety valve," resulting in a slower increase in carbon dioxide levels than the glass jar while blocking the entry of external particles. Their data revealed that the carbon dioxide level in onggi was less than half of that in glass containers.

They also found that the beneficial bacteria in the onggi-made kimchi proliferated 26% more than in the glass counterpart. In the glass jar, the lactic acid bacteria became suffocated by their own carbon dioxide in the closed glass container. It turns out that, because the onggi releases carbon dioxide in small rates, the lactic acid bacteria are happier and reproduce more.

[...] "It's amazing that, for thousands of years, people have been building these special containers out of dirt, but in many ways, they are very high tech," Hu said. "We discovered that the right amount of porosity enables kimchi to ferment faster, and these onggi provide that."

Kim said that some artisans still use ancient methods when making onggi, but their numbers are decreasing. Now, the market is flooded with inauthentic versions of the vessels.

"We hope this study draws attention to this traditional artisan work and inspires energy-efficient methods for fermenting and storing foods," he said. "Also, the onggi are quite beautiful."

Journal Reference:
Kim Soohwan and Hu David L. 2023 Onggi's permeability to carbon dioxide accelerates kimchi fermentation J. R. Soc. Interface 20 http://doi.org/10.1098/rsif.2023.0034 [doi.org]

Original Submission