What Is Onggi? Traditional Fermentation Jars of Korea

Korean clay jars - onggi

Before there were refrigerators or even kimchi fridges, Koreans stored their food in clay jars called onggi (옹기). These beautiful, earth-toned vessels weren’t just containers—they were living tools that made fermentation possible long before modern technology.

 

Let’s explore what makes onggi so special, and why some Korean families still prefer them for fermenting kimchi, doenjang (soybean paste), gochujang (red chili paste), and soy sauce.

What Exactly Is Onggi?

Onggi are traditional Korean earthenware jars made from breathable clay. They’ve been used for over 2,000 years to store and ferment food. What makes them unique is their porous surface, which allows air circulation while keeping out contaminants. This balance is perfect for controlled fermentation.

There are various types of onggi: some tall and narrow for sauces, others wide and deep for kimchi. Most are brown, with a glazed finish and subtle texture from the clay’s natural firing process.

How Were Onggi Used?

In traditional Korean homes, large onggi jars were often kept outside in a designated corner of the yard, called a jangdokdae (장독대). They held:

• Kimchi – stored underground or in shaded areas to ferment slowly
• Doenjang & Gochujang – fermented for months or years
• Soy Sauce (Ganjang) – naturally aged using sunlight and airflow

A pair of hands carefully stuffs spicy seasoning into napa cabbage leaves—a classic scene from Korea’s kimjang tradition. [ⓒPhoto Korea - Kim Jiho]

A row of onggi jars sits outdoors as a person carefully lifts the lid to check the fermentation process—a timeless Korean tradition. [ⓒPhoto Korea - Park Eun Kyoung]

The jars were sealed with cloth or heavy lids and weighted stones, allowing gases to escape while blocking pests.

The Science Behind Onggi

Modern studies have shown that onggi's micropores allow gas exchange while limiting excess moisture. This helps beneficial bacteria thrive during fermentation.

Compared to glass or plastic, onggi provides a more stable, natural environment for long-term fermentation—similar to wine cellars or cheese caves in other cultures.

Onggi's micropores allow gas exchange while limiting excess moisture.

Onggi Today: Still Alive in Korean Kitchens

While kimchi fridges have become the norm in urban apartments, some people—especially those living in the countryside—still use onggi. You’ll also find them at Korean traditional markets or pottery villages like Icheon and Onggi Village in Ulsan.

Recently, onggi has gained attention among international chefs and fermenters looking for natural materials and ancient techniques.

How to Clean and Care for Onggi

Onggi jars are natural, chemical-free fermentation vessels—and they need to be treated with care. Here’s how to clean and store them properly.

1. Cleaning Onggi Before Use

• Mix water with one of the following: salt, vinegar, or baking soda for sterilization. (Just water is also fine, since onggi is chemical-free.)
• Use a soft sponge to gently clean the inside and outside. Avoid harsh scrubbers.
• Rinse thoroughly with clean water.
• Let the onggi air dry in the sun for about one day. (If you plan to store rice, make sure it's completely dry.)

2. Important Cautions

• Do not expose to sudden temperature changes. Avoid pouring hot water into a cold jar or placing it in freezing conditions.
• Sudden heating or cooling can cause cracks. Always bring the jar to room temperature first.

Do not expose onggi to sudden temperature changes.

3. Natural Characteristics to Expect

• Color variations: Onggi is glazed with natural ash, so each piece may look slightly different—this is normal.
• White stone powder: You may see small white particles inside and outside. These are harmless residues from the kiln process.
• Imperfect logo stamps: The brand logo may appear faint or irregular. This happens with hand-stamped jars and is not a defect or fake product.

4. Modern Tips for Using Onggi

Today, many Koreans use onggi jars with transparent glass lids instead of traditional clay lids. These allow users to check the fermentation status without opening the jar and exposing it to air. Some households even reuse wide, flat glass pot lids that fit snugly over the onggi opening.

For making large batches of kimchi (especially during gimjang season), it’s common to line the onggi jar with a kimchi storage bag—a thick, food-grade plastic liner. This makes cleaning easier and helps control moisture and odor inside the jar.

Does Using a Kimchi Bag in Onggi Affect Fermentation?

Lining onggi jars with thick kimchi bags is a common practice in modern Korean homes. It makes cleanup easier and prevents staining or odors inside the clay jar.

Some fermentation experts prefer using onggi without plastic liners to allow full air interaction through the porous walls. However, for most home cooks, using a bag does not significantly affect the fermentation process—especially for short to medium-term storage (1–3 months).

Just make sure the bag is food-grade and loosely placed, not fully sealed airtight, so the fermentation gases can still escape.

“Onggi is a living tool—it breathes, ferments, and carries generations of wisdom. Handle it with respect, and it will take care of your food.”

Onggi vs. Modern Containers

Feature	Onggi	Modern Containers
Material	Breathable clay	Glass, plastic, or steel
Airflow	Yes – allows gentle gas exchange	No – airtight
Fermentation Style	Slow, natural	Controlled, stable
Flavor Development	Deep, earthy complexity	Clean, consistent taste

Korean Fermenting Onggi Jars

Coming Up Next…

Next, let’s take a closer look at doenjang—Korea’s fermented soybean paste—and how it’s traditionally made in onggi jars.

Up next: What Is Doenjang? Korea’s Fermented Flavor Bomb