How Kimchi Is Made: The Process Behind Controlled Fermentation

FRANVIA | K-TODAY

Korea’s everyday life — tradition, as it lives today

Kimchi production is not cooking. It is the management of microbial activity through salting, seasoning, and environmental control. The process transforms raw vegetables into preserved food by creating conditions that favor lactic acid bacteria while suppressing spoilage organisms. Understanding how kimchi is made means understanding how each step manipulates chemistry, microbiology, and time to achieve a specific outcome.

The method is structured but not rigid. Each decision—how long to salt, how much seasoning to apply, where and how long to ferment—affects the final product. These decisions are informed by the vegetable being used, the season, the intended storage period, and the flavor preferences shaped by regional tradition. The process is therefore adaptive, requiring judgment rather than mechanical repetition.

This article explains the functional stages of kimchi production and the reasoning behind each step. It does not provide recipes or measurements, but rather clarifies why the process works the way it does and how variables within each stage alter the result.

Kimchi paste is gently placed
between each salted cabbage leaf
to ensure even seasoning before fermentation.

Top-down view showing the kimchi-making process,
including salted napa cabbage,
seasoning ingredients, and jars
prepared for fermentation.

Selecting and Preparing the Base Vegetable

The first stage is selecting the vegetable and preparing it for salting. The vegetable's structure, water content, and cell composition determine how it must be handled.

Napa cabbage is typically halved or quartered lengthwise to expose the inner layers while keeping the core intact. This allows brine to penetrate evenly while maintaining structural integrity. The cabbage is inspected for damaged or wilted leaves, which are removed. Leaving damaged tissue can introduce unwanted microbes or create uneven fermentation.

Radish for kkakdugi is peeled and cut into uniform cubes, usually between one and two centimeters. Uniformity ensures even salting and fermentation. Irregular pieces result in some sections fermenting faster than others, leading to inconsistent texture and flavor.

Leafy vegetables like mustard greens or young radish greens are trimmed and washed carefully. Because their cell walls are thinner than cabbage or radish, they absorb salt more quickly and ferment faster. They are often left whole or cut into large sections to preserve structure during fermentation.

Washing is critical but must be balanced. Vegetables are rinsed to remove soil and surface contaminants, but excessive washing can strip away naturally occurring bacteria that contribute to fermentation. Traditional methods used well water or clean running water without detergents. Modern producers may use filtered or dechlorinated water to avoid introducing chlorine, which inhibits lactic acid bacteria.

The preparation stage is where the maker begins controlling the fermentation outcome. The way the vegetable is cut, how much surface area is exposed, and how thoroughly it is cleaned all influence how salt penetrates and how seasoning adheres.

Salting: Creating the Conditions for Fermentation

Salting is the most critical step in kimchi production. It serves three purposes: drawing water from the vegetable cells to create brine, establishing an environment hostile to pathogenic bacteria, and beginning the process of texture modification that continues through fermentation.

There are two primary salting methods: dry salting and brine soaking. The choice depends on the vegetable's water content and structure.

Dry salting involves rubbing coarse salt directly onto the vegetable, particularly between the layers of cabbage leaves or onto the cut surfaces of radish. The salt draws water out through osmosis, and the vegetable's own moisture forms a brine. This method gives the maker more control over salt distribution and is often used when a firmer final texture is desired. The vegetable is typically left to sit for several hours, during which it is turned or massaged periodically to ensure even salting.

Brine soaking involves submerging the vegetable in a salt solution. The concentration of the brine determines how quickly water is drawn from the cells. A typical brine ranges from 5% to 10% salinity, though this varies by region and vegetable type. Cabbage is often soaked in brine for four to eight hours, sometimes longer. The vegetable is weighted down to keep it submerged, ensuring uniform exposure to the salt solution.

During salting, the vegetable loses rigidity as water leaves the cells. Cabbage leaves become pliable, radish cubes soften slightly, and leafy greens wilt. This textural change is necessary for seasoning to penetrate and for fermentation to proceed evenly.

The vegetable is then rinsed to remove excess surface salt. This step is important because too much residual salt can inhibit fermentation or make the final product unpalatably salty. The vegetable is usually rinsed once or twice with clean water, then drained thoroughly. Some water remains in the cells and between the layers, which becomes part of the fermentation brine.

Salting time and salt concentration are adjusted based on temperature and intended fermentation speed. In winter, longer salting with higher salt levels slows fermentation and extends shelf life. In summer, lighter salting and shorter times prevent over-fermentation in warm conditions.

Coarse salt is applied
between napa cabbage leaves
to draw out moisture
and prepare the cabbage for fermentation.

Napa cabbage leaves after salting, softened
and ready for seasoning and fermentation.

Preparing the Seasoning Paste

The seasoning paste is where flavor complexity is built. It is a mixture of aromatics, spices, fermented ingredients, and sometimes fruits or vegetables that contribute sugars, enzymes, and microbial cultures to the fermentation.

The base of most seasoning pastes includes garlic, ginger, and gochugaru. Garlic is crushed or minced to release allicin and other sulfur compounds. These compounds have antimicrobial properties that selectively inhibit certain bacteria while allowing lactic acid bacteria to thrive. Ginger is grated or finely chopped, adding warmth and slight sweetness while contributing gingerol compounds that also affect microbial activity.

Gochugaru is mixed into the paste to achieve the desired level of heat and color. The chili powder must be evenly distributed to avoid concentrated pockets of spice. Some makers lightly toast or bloom the gochugaru in a small amount of oil to intensify its color and flavor, though this is not universal.

Fermented seafood is added to provide umami, salt, and enzymatic activity. Salted shrimp is commonly used, either whole or crushed. Fish sauce or anchovy sauce may be added for liquid and concentrated flavor. The type and amount of fermented seafood vary significantly by region and personal tradition. Coastal regions tend to use more and varied types, while inland areas may use less or substitute with vegetable-based umami sources.

Julienned radish, scallions, and sometimes onions are incorporated into the paste. Radish adds texture and releases sugars during fermentation, feeding lactic acid bacteria and contributing to brine development. Scallions provide sharpness and aromatic intensity. Onions, when used, add sweetness and help bind the paste.

Korean pear, apple, or other fruits are sometimes blended into the paste. These ingredients serve multiple functions: they add natural sugars that accelerate fermentation, contribute pectin that helps the paste adhere to vegetables, and provide subtle sweetness that balances salt and spice. Not all kimchi includes fruit, and its use depends on regional practice and the maker's intent.

Some recipes include glutinous rice porridge or sweet rice flour paste. This thickens the seasoning mixture and provides additional sugars for fermentation. The porridge is cooked and cooled before being mixed with other ingredients. It creates a smoother, more cohesive paste that clings to vegetable surfaces more effectively.

The proportions of these ingredients are not fixed. A maker adjusts based on the vegetable being used, the season, and the desired flavor profile. Heavier vegetables like radish may require a denser paste, while delicate greens need lighter seasoning. Winter kimchi intended for long storage may have more salt and fermented seafood, while summer kimchi uses lighter, fresher flavors.

 Ingredients for seasoning paste
arranged in small bowls
including gochugaru, minced garlic,
grated ginger, and salted shrimp

Applying Seasoning and Packing for Fermentation

Once the seasoning paste is prepared, it is applied to the salted vegetables. This step requires attention to ensure even distribution and proper packing to create the anaerobic environment necessary for fermentation.

For whole or halved cabbage, the paste is spread between each layer of leaves, working from the outermost leaves toward the core. The maker uses hands to massage the paste into the crevices, ensuring contact with all surfaces. The outer leaves are then folded over to enclose the seasoned interior, creating a compact package that minimizes air exposure.

For cubed radish or other cut vegetables, the seasoning paste is mixed directly with the pieces in a large bowl. The mixture is tossed and massaged until each piece is evenly coated. This method ensures uniform flavor distribution and encourages brine formation as the salt in the paste continues to draw moisture from the vegetables.

The seasoned vegetables are then packed into fermentation containers. Traditional earthenware onggi are still used by some households, but glass jars, plastic containers, and purpose-built kimchi refrigerators are now common. The choice of container affects fermentation because different materials interact differently with temperature and gas exchange.

Packing must be tight to minimize air pockets. Air allows aerobic bacteria to grow, which can lead to surface mold or off-flavors. The vegetables are pressed down firmly, and any remaining seasoning paste or liquid is poured over the top. If there is insufficient liquid to cover the vegetables, a small amount of salted water may be added to ensure submersion.

A weight is sometimes placed on top of the packed vegetables to keep them submerged as fermentation begins and gases are released. This weight can be a clean stone, a smaller jar filled with water, or a purpose-made fermentation weight. The goal is to prevent the top layer from being exposed to air.

The container is then sealed, though not airtight. Fermentation produces carbon dioxide, which must be allowed to escape. Traditional onggi have porous lids that permit gas exchange while keeping contaminants out. Modern containers may be loosely covered or equipped with airlocks that allow gas to exit without letting air in.

Fermentation: Temperature, Time, and Microbial Succession

Fermentation is where salt, seasoning, and vegetables interact with microbial communities to produce the flavors, textures, and preservation characteristics of kimchi. This stage is governed by temperature and time, and the maker's role is to control these variables to achieve the desired result.

In the initial phase, a diverse community of bacteria begins to multiply. As the environment becomes more acidic due to lactic acid production, acid-tolerant species dominate while others decline. This microbial succession is predictable but sensitive to conditions.

At cool temperatures (4–7°C), fermentation proceeds slowly. Lactic acid bacteria multiply gradually, and flavor develops in layers over weeks or months. The vegetables retain more of their original texture, and the flavor remains balanced rather than intensely sour. This slow fermentation is traditional for winter kimchi, which was historically made in large quantities in late autumn and stored in buried onggi or cool cellars.

At moderate temperatures (10–15°C), fermentation accelerates. The kimchi reaches peak flavor in one to two weeks. This is a common temperature range for household kimchi production, as it allows for relatively quick consumption without requiring extended storage.

At warm temperatures (18–25°C), fermentation happens rapidly. Summer kimchi made in these conditions can be ready in two to three days. However, the risk of over-fermentation increases. If left too long, the kimchi becomes excessively sour, the vegetables lose structural integrity, and off-flavors may develop. Summer kimchi varieties are designed for this rapid cycle and are typically consumed quickly.

During fermentation, the kimchi is monitored for signs of progress. Bubbles appear as carbon dioxide is released. The brine becomes cloudy as bacteria multiply. The smell shifts from raw vegetable and pungent seasoning to a tangy, fermented aroma. The flavor becomes increasingly sour as lactic acid accumulates.

Tasting is the primary method of determining when kimchi is ready. The maker samples the kimchi periodically, assessing sourness, texture, and flavor balance. Readiness is subjective and depends on preference, but there are general indicators: the vegetables should be tender but still have bite, the flavor should be tangy without being harshly acidic, and the brine should taste clean rather than funky or off.

Once the desired fermentation level is reached, the kimchi is transferred to cold storage to slow further fermentation. Modern refrigeration maintains a consistent cool temperature that preserves the kimchi in its peak state for weeks or months. Traditional methods relied on cool cellars or buried pots, which kept kimchi cold through winter but warmed as spring arrived, requiring consumption before over-fermentation occurred.

[Image: Glass jar showing kimchi at different fermentation stages with visible bubble formation and color changes]

Managing Fermentation Variables

Successful kimchi production requires managing multiple variables simultaneously. Each decision influences the others, and the maker must adjust based on real-time observation rather than following a fixed formula.

Salt concentration affects fermentation speed and final flavor. Too little salt allows rapid bacterial growth but increases the risk of spoilage. Too much salt inhibits fermentation and makes the kimchi unpalatably salty. The maker must calibrate salt levels based on the vegetable's water content, the ambient temperature, and the intended storage period.

Seasoning density influences flavor intensity and microbial activity. A thick, heavily seasoned paste creates bold, complex flavors but may slow fermentation slightly. A lighter paste allows the vegetable's natural flavor to remain more prominent and ferments more quickly. Regional traditions and personal preference guide this choice, but the vegetable's structure also matters. Dense vegetables like radish can support heavier seasoning, while delicate greens require restraint.

Container choice affects temperature stability and gas exchange. Earthenware breathes, allowing slow gas exchange that some believe improves flavor complexity. Glass and plastic are non-reactive and allow visual monitoring but do not breathe. Kimchi refrigerators are designed to maintain optimal fermentation and storage temperatures, cycling through slight temperature variations that some users believe enhance flavor development.

Air exposure is a constant concern. Even small amounts of oxygen at the surface can lead to mold growth or oxidation that discolors the kimchi and produces off-flavors. Keeping vegetables submerged and minimizing headspace in the container reduces this risk.

The maker must also account for batch size. Large batches ferment differently than small ones because of thermal mass and surface-area-to-volume ratios. A large batch in a traditional onggi maintains stable temperature more easily than a small jar in a fluctuating environment. This is one reason traditional kimjang—the communal kimchi-making event in late autumn—produced such large quantities. The volume itself contributed to successful fermentation and long-term storage.

Post-Fermentation Handling and Storage

Once kimchi reaches the desired fermentation level, handling practices determine how long it maintains quality and how its flavor evolves during storage.

Kimchi stored at refrigeration temperatures (2–4°C) continues to ferment, but very slowly. Over weeks and months, the flavor becomes more sour and the texture softens. This gradual change is often desirable, as many people prefer well-aged kimchi for certain dishes like kimchi stew or fried rice. The increasing acidity also acts as a preservative, extending shelf life.

When removing kimchi from the container, clean utensils should be used to avoid introducing contaminants. The kimchi should remain submerged in brine, so if liquid levels drop, the maker may add a small amount of salted water to maintain coverage. Exposure to air during storage increases the risk of surface mold.

If white film or spots appear on the surface, this is usually harmless yeast or mold that can be skimmed off. The kimchi beneath remains safe to eat as long as it smells and tastes normal. However, extensive mold growth, particularly if it appears fuzzy or colored, indicates spoilage, and that portion should be discarded.

Over-fermented kimchi that has become too sour for eating fresh is not wasted. It is used in cooked applications where its strong acidity and soft texture are assets. Kimchi jjigae, a spicy stew, relies on sour kimchi for its characteristic tang. Kimchi pancakes and fried rice also benefit from the concentrated flavor of aged kimchi. This repurposing reflects the practical approach to fermentation: even past its prime for one use, kimchi remains valuable for another.

Some households maintain a rotation of kimchi at different fermentation stages. Fresh kimchi is eaten as a side dish, moderately fermented kimchi is used for wraps or rice accompaniment, and fully soured kimchi is reserved for cooking. This approach ensures continuous use and reduces waste.

Kimchi seasoning carefully layered
between salted cabbage leaves
before fermentation.

Fully seasoned kimchi
neatly gathered and prepared for
storage and fermentation.

Finished kimchi arranged on a plate,
ready to be served at the table.

Seasonal Production Cycles and Kimjang Tradition

Kimchi production in Korea was historically governed by agricultural cycles and seasonal temperature patterns. The most significant production event was kimjang, the late autumn preparation of winter kimchi.

Kimjang typically occurred in November or early December, after the final harvest of napa cabbage and radishes but before the first hard freeze. Extended families and neighbors gathered to process large quantities of vegetables—sometimes hundreds of heads of cabbage—over one or two days. The work was divided: some cleaned and salted vegetables, others prepared seasoning paste, and others packed the finished kimchi into storage vessels.

The timing of kimjang was critical. Too early, and the kimchi would over-ferment before winter cold slowed the process. Too late, and freezing temperatures would damage the vegetables before they could be processed. The work required careful observation of weather patterns and coordination across households.

The kimchi produced during kimjang was intended to last through winter and into early spring, a period of several months when fresh vegetables were unavailable. The large volume meant that even as fermentation continued in storage, the household would consume kimchi at different stages of sourness throughout the season.

Modern refrigeration and year-round vegetable availability have reduced the necessity of kimjang, but the tradition persists as a cultural practice and social event. Many urban households still participate, though on a smaller scale than in rural areas or previous generations. The practice reinforces family bonds, transmits knowledge across generations, and maintains connection to agricultural rhythms even in industrialized settings.

Summer kimchi production followed a different pattern. Small batches were made frequently using seasonal vegetables like cucumbers, young radish greens, or scallions. These kimchis were consumed within days rather than stored for months. The goal was not preservation but utilization of abundant summer produce and provision of light, refreshing side dishes suited to hot weather.

Why Kimchi-Making Is Knowledge, Not Recipe

Understanding kimchi production requires recognizing that it is knowledge-based practice, not rule-following. The process involves principles that apply across all kimchi types, but the specific actions taken depend on variables that change with every batch: the vegetable's water content, the ambient temperature, the desired storage period, and the intended use.

A maker develops judgment through experience. They learn to assess when cabbage has been salted enough by how pliable the leaves feel. They adjust seasoning paste density based on how the vegetable will be eaten—fresh or aged, alone or in cooking. They determine fermentation readiness through taste, smell, and appearance rather than adherence to a fixed timeline.

This knowledge is often transmitted within families and communities rather than through written instructions. A person learns by observing, assisting, and eventually making their own batches under guidance. Mistakes—over-salting, under-seasoning, letting fermentation proceed too far—become learning experiences that refine technique.

This is why kimchi made by different people, even using similar ingredients and methods, can taste noticeably different. The accumulated judgments made throughout the process compound into distinct outcomes. One maker's "properly fermented" is another's "too sour" or "not ready yet." These differences are not errors but reflections of the adaptive, judgment-based nature of the practice.

Industrial kimchi production standardizes these variables to ensure consistency across batches. Manufacturers use controlled environments, precise ingredient measurements, and regulated fermentation times. The result is predictable and reliable, but it represents a single path through the decision space that traditional kimchi-making occupies. The industrial product sacrifices the variation inherent in the craft for the sake of scalability and consistency.

For anyone learning to make kimchi, the task is not to find the "correct" method but to understand the logic that connects each step to the desired outcome. Salt draws water and creates conditions for fermentation. Seasoning introduces flavor and microbial cultures. Temperature controls fermentation speed. Time allows complexity to develop. These principles remain constant, even as the specific actions taken vary with circumstances.

Kimchi-making is fermentation literacy—the ability to read the signs of microbial activity, to adjust conditions in response to what is observed, and to guide a living process toward a desired end state. This literacy is applicable beyond kimchi to other fermented foods and to the broader understanding of how preservation, flavor, and nutrition intersect through microbial transformation.

 

Explore more perspectives on Korean food and culture in our previous articles.

• What Kimchi Is and Why It Takes Many Forms
• Fermentation Science — The Quiet Engine of Korean Flavor | Kimchi, Jang, and Makgeolli Explained
• Kimchi Salt Ratios Explained for First-Time Fermenters
• Kimchi That Works: The Real Salt Ratios and Timelines You Need
• Kimchi Craze: Why This Spicy Fermented Side Dish Became a Global Superstar

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