In my household, my onggi are prized possessions. Not only are they super functional, but they’re also beautiful. In fact, they sit on my kitchen counter 24/7 even when I’m not actively fermenting a batch of kimchi or kkakdugi. That’s how much I love them.
Onggi, or Korean “earthenware crocks”, are made from clay and sand. When fired in a kiln, the vessel is left with microscopic pores. These holes allow for breathing, yet the end result is still water tight, making onggi ideal for fermentation. The glaze on the exterior of the onggi is made of wood ash and leaf mold and once applied, the onggi is fired in a kiln again. The science behind the firing sequences and the combination of the natural materials has been crafted and perfected over thousands of years. Though there are many more modernized devices for fermentation available today, my preference is to use the onggi because of the history and its environmentally friendly production. Here is a wonderful video on the creation of onggi.
Onggi are kitchen essentials in Korean households. These crocks are one stop shop devices that have been traditionally used to preserve many foods in the Korean culture, ranging from fermented salty fish, to soybean paste, to of course, kimchi. Traditionally, onggi are kept in clusters outside of the home on a terrace referred to as jangdokdae. During the winter in Korea, the onggi are buried in the ground to prevent the kimchi or other fermenting foods from freezing.
In my humble opinion, onggi are the OG fermentation vessel. Of course I’m shamelessly biased because I’m Korean, but hear me out on this. Korean onggi are like a cast iron skillet— they get better and better with time. Because of the microporous structure of onggi, the beneficial bacteria and enzymes from the previous fermentations are retained in the walls. The next time you use it, your ferment happens faster and the flavors are better. In a lot of ways, fermenting in onggi is like composting. The residual microorganisms jump start the next batch.
You may be wondering now, how do you clean it? The answer is, you sort of clean it. Because of the porous structure, you cannot use soap with onggi. Why? You guessed it— the soap will get trapped in the pores and then leach into your food. To clean an onggi, scrub it with warm water. Some of the kimchi smell will remain, but that’s ok. If you do want to give the onggi a deep clean, soak it in hot water with a dash of vinegar and leave it for 24 hours. Repeat the process if desired.
So let’s talk about the elephant in the room. Is it safe? I know all of you are wondering about this because yes, onggi are not air tight. Understand that fermentation is completely different than canning. That being said, many modern fermentation practices stress the need to fully submerge your food beneath a liquid salt brine and to use only air tight containers. While you do want to make sure you pack your kimchi down tightly when you’re filling your onggi, your kimchi will not be submerged beneath inches of liquid during the first few days of fermentation, and that is perfectly normal. Just pack it down as much as you can and make sure the surface is pretty much covered with kimchi paste, or kimchi juice if your ferment has been going for a few days.
If you are familiar with kimchi preparation or if you read My Homemade Kimchi Recipe, you know that for the first handful of days, kimchi ferments at room temperature. Those of you who are terrified of giving yourself or your loved ones botulism, you can take a breath and relax. Lacto-fermentation produces lactic acid, which creates an inhospitable environment for the bacteria that cause botulism. The beneficial lactobacillus bacteria, coupled with a salty brine, prevent the harmful bacteria from living in your ferment. So get your ferment on and rest assured that you will be fine!
The only thing I have ever run into with fermenting in onggi is a small amount of isolated white mold formation on some kkakdugi, and that is because it was left on the counter a little too long. With that being said, I’ve only had it happen once. This is why in my fermentation recipes, I do not advise people to ferment at room temperature for longer than 5-6 days. After one week, I’ve found that the probability for mold increases, so the kimchi needs to be moved into the fridge for storage and/or to continue fermenting. Even when this happened, I removed the moldy portion, transferred the kkakdugi into a jar, and moved it into the fridge. I continued to eat it for weeks with no problems. I know it is scary to let food sit on the counter in 70-75 degree temperatures, especially when seafood is part of the ingredient list, but trust me, people have been doing this for thousands of years, way before refrigerators!
In fact, fermenting in onggi has actually been proven to produce more desirable results than other more modern vessels for fermentation. The lactobacillus populations have been measured in some studies to be higher than those fermented via other mediums. If you feel like nerding out, here is the link to the abstract. You can request the full article if desired. This doesn’t at all mean that other vessels don’t ferment well, but it does go to show that thousands of years of practice have paid off for the Koreans and that there is some merit to the design and functionality of traditional onggi. If I haven’t convinced you to pick up an onggi, or if onggi are just nowhere to be found in town or online, using a glass mason jar will still get you fantastic results.
For me, fermenting my own kimchi in onggi makes me feel one with my heritage. I truly believe there is value in continuing the practices of my ancestors, and I can taste the difference in the kimchi I make. I hope you consider picking up an onggi and trying your hand at traditional Korean fermentation.