Kimchi, a Korean fermented delicacy, is popular throughout the world, made by activity of billions of microbes. Ingredients vary but usually include napa cabbage, Korean radish and a variety of spices.
A traditional vegetable dish of Korea, its origins trace back over 2,000 years. Many regional varieties exist. Flavors vary widely, from tangy and spicy to sweet and sour.
Often eaten as a side dish, it can also be incorporated into stews, soups, stir-fries and pancakes. Kimchi is a symbol of Korean identity and heritage. In many households it's a daily basic.
Creation of kimchi is often a communal effort. This happens especially during kimjang, when families and communities prepare large batches for winter. Clay vessels can be used; glass is popular today.
Kimchi is fermented using wild cultures naturally found on the vegetables.
Microorganisms of kimchi production are lactic acid bacteria (LAB), acetic acid bacteria and yeast. These three microbe types often travel together.
LAB dominate the process, developing in the initial phases of kimchi fermentation. Yeast appears during the intermediate stages, and may form a harmless thin whitish skin on top. Further LAB flourish later in the process.
In anerobic fermentation, yeast consume sugars to produce CO2, hence some of the outgassing, and a small amount of ethanol. In finished kimchi alcohol is fundamentally non-existent.
It's transformed to acetic acid by the acetic acid bacteria. The acidity and salt eliminate pathogens like the botulism bacteria Clostridium botulinum, which can't survive pH below 4.6; and Salmonella (pH 6.5 - 7.5).
Acetobacter species continue to oxidize the acetic acid they produce into CO2 and H2O, in a process of acetate oxidation or overoxidation. This can cause higher levels of sourness. Gluconobacter spp lack this ability.
In aerobic or oxygen-based fermentation the yeast produce CO2 and water. Acetic acid bacteria are aerobic, as opposed to LAB and yeast who prosper in anaerobic conditions.
The lid of the kimchi fermentation jar should not be tight. Screw-on lids can be left loose to allow gases to escape and promote conditions for AAB. Glass vessels with tight lids can explode.
Production of organic acids, mainly lactic and acetic acid, creates an ideal kimchi pH of 4.2. While ingredients can vary, a few components are essential to the kimchi-making process.
These include:
Napa Cabbage (Baechu) Brassica rapa: This is the most common base for kimchi, providing a crisp texture and a mild sweetness that balances the other flavors.
Korean Radish (Mu): Longer and thicker than the commonly found radish, the Korean radish offers a refreshing, slightly peppery bite.
Gochugaru (Korean Chili Powder): This vibrant red chili powder gives kimchi its characteristic color and heat. Gochugaru comes in varying degrees of coarseness and spice levels.
Salt: Salt draws out moisture from the vegetables, creating an environment conducive to fermentation.
Aromatic Vegetables: Garlic, ginger, and scallions are essential for adding depth and complexity to the flavor.
Fermentation Starters: Ingredients like jeotgal (fermented seafood sauce) or saeujeot (fermented shrimp) may be used to kickstart the fermentation process and add umami richness.
The Kimchi-Making Process
Making kimchi is a tradition passed down through generations. The first step is choosing a high-quality napa cabbage. Poor quality, limp or old cabbage is a sure fail. Cabbage is washed and cut it into quarters.
Salting the Cabbage: The napa cabbage is heavily salted, covered and left to sit for several hours or overnight. Salt draws out moisture, softens the leaves, and inhibits growth of undesirable bacteria.
Preparing Kimchi Paste: While cabbage is salting, the other ingredients are prepared. The radish, garlic, ginger, and scallions are chopped or grated. The gochugaru, jeotgal or saeujeot, and other spices are combined to create a paste.
Rinsing and Draining: After the salting period, cabbage is thoroughly rinsed to remove salt. It's then drained completely.
Mixing It Together: The kimchi paste is rubbed into each leaf of the cabbage, ensuring every part is coated.
Packing and Fermenting: The kimchi is packed tightly into jars or fermentation containers, leaving some space at the top to allow expansion.
The mix ferments at room temperature (20°C or 68°F) for a few days, contingent on desired sourness. Fermentation transforms the raw ingredients into the complex and flavorful kimchi.
During fermentation, lactic acid bacteria like Lactobacillus spp. break down carbohydrates in the vegetables, producing lactic acid. Along with acetic acid, this contributes to the sourness of kimchi.
Lactobacillus also produces many of enzymes associated with humans. Primary enzymes identified include lactase, proteases, fructanases, amylases, bile salt hydrolases, phytases, and esterases.
Lactobacilli occur naturally in soil and organic matter, as well as in the human digestive system. In the body and environment, Lactobacilli suppress harmful enzymes released by pathogens.
Kimchi can ferment at room temperature for 1 to 5 days. Fermentation length influences flavor. Warm temperatures stimulate activity of microbes to accelerate the process, but too much warmth can spoil the food.
After a few days, kimchi is put in a cold place like the fridge. This slows fermentation and allows the flavors to mature gradually.
Even in the fridge the process cannot fully be stopped. Over-sour kimchi is often used as a tangy flavoring.
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