Kimchi is a conventional Korean meal made from fermented vegetables, typically cabbage and radishes, skilled with numerous spices and spices. It is known for its unique appetizing and hot taste, resulting from the fermentation procedure. Kimchi is a staple in Korean food and is typically taken in as a side meal or used as an active ingredient in other meals, adding a unique and tasty element to meals.
Kimchi, a type of fermented food, has actually been a main component of Korean cuisine for centuries. In ancient times, Korean cooking experts used onggi, clay jars crafted by hand, for the fermentation of kimchi. While the modern-day production of kimchi predominantly counts on mass fermentation processes utilizing containers made of steel, glass, or plastic, its extensively thought that onggi-fermented kimchi boasts remarkable quality.
This long-held belief among kimchi connoisseurs has actually now received scientific recognition due to recent research study carried out by David Hu, a professor at the George W. Woodruff School of Mechanical Engineering at Georgia Tech, along with Soohwan Kim, a Ph.D. trainee presently in his 2nd year under Hus assistance.
In a combined experimental and theoretical research study, Hu and Kim determined carbon dioxide levels in onggi during kimchi fermentation and developed a mathematical design to demonstrate how the gas was produced and moved through the onggis porous walls. By bringing the research study of fluid mechanics to bear on an ancient innovation, their research study highlights the work of craftsmens and offers the missing link for how the traditional earthenware enables for premium kimchi.
A cross-sectional view of onggi showing fermenting cabbage. Credit: Korean Ministry of Culture, Sports, and Tourism.
Their research study was published in the Journal of the Royal Society Interface.
” We desired to discover the secret sauce for how onggi make kimchi taste so great,” Hu stated. “So, we measured how the gases developed while kimchi fermented inside the onggi– something nobody had actually done before.”
The porous structure of these earthenware vessels imitates the loose soil where lactic acid germs– understood for their healthy probiotic nature– are discovered. While previous studies have revealed that kimchi fermented in onggi has more lactic acid bacteria, nobody understood exactly how the phenomenon is linked to the distinct material residential or commercial properties of the container.
First, Kim acquired a standard, handcrafted onggi container from an artisan in his hometown of Jeju, South Korea, an area well-known for onggi. Back at Georgia Tech, Hu and Kim first checked the permeability of the onggi by observing how water vaporized through the container in time.
David Hu (ideal), teacher of mechanical engineering at Georgia Tech, and Soohwan Kim, a second-year Ph.D. student, with the onggi they utilized in fermentation experiments. Credit: Georgia Institute of Technology
Next, they set up carbon dioxide and pressure sensors into both the onggi and a normal, hermetically sealed glass container. They prepared their own salted cabbage and placed it in both containers. They then utilized the sensing units to compare the change and determine in carbon dioxide– a signature of fermentation.
Hu and Kim also established a mathematical model based on the porosity of the onggi. The model allowed them to infer the generation rate of co2, given that the onggi lets co2 out slowly.
They concluded that the onggis porous walls permitted the carbon dioxide to get away the container, which accelerated the speed of fermentation. The onggis porosity likewise operated as a “security valve,” resulting in a slower increase in carbon dioxide levels than the glass container while obstructing 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 helpful bacteria in the onggi-made kimchi multiplied 26% more than in the glass counterpart. In the glass jar, the lactic acid germs became suffocated by their own carbon dioxide in the closed glass container. It turns out that, due to the fact that the onggi launches carbon dioxide in small rates, the lactic acid germs are happier and recreate more.
” Onggi were created without modern understanding of chemistry, fluid, or microbiology mechanics, however they work incredibly well,” Kim said. “Its extremely interesting to get these new insights into ancient innovation through the lens of fluid characteristics.”
Onggis semi-porous nature is unique compared to other types of earthenware. A clay container that leaks, but only slightly, is difficult to make. Terra-cotta containers, for example, quickly leak water.
” Its fantastic that, for thousands of years, people have actually been constructing these special containers out of dirt, however in lots of ways, they are very modern,” Hu stated. “We discovered that the ideal quantity of porosity allows kimchi to ferment quicker, and these onggi supply that.”
Kim said that some artisans still use ancient approaches when making onggi, but their numbers are decreasing. Now, the market is flooded with inauthentic variations of the vessels.
” We hope this study accentuates this standard artisan work and inspires energy-efficient approaches for fermenting and saving foods,” he stated. “Also, the onggi are rather stunning.”
Reference: “Onggis permeability to co2 accelerates kimchi fermentation” by Soohwan Kim and David L. Hu, 5 April 2023, Journal of The Royal Society Interface.DOI: 10.1098/ rsif.2023.0034.
The research study was moneyed by the National Science Foundation.
In ancient times, Korean culinary specialists utilized onggi, clay containers crafted by hand, for the fermentation of kimchi. Next, they installed carbon dioxide and pressure sensing units into both the onggi and a common, hermetically sealed glass container. They concluded that the onggis porous walls permitted the carbon dioxide to escape the container, which sped up the speed of fermentation. The onggis porosity also operated as a “security valve,” resulting in a slower increase in carbon dioxide levels than the glass container while blocking the entry of external particles. Their data exposed that the carbon dioxide level in onggi was less than half of that in glass containers.
