There are hundreds of styles of kimchi and as many variations as cooks who make it. But preparing iconic tongbaechu-kimchi, the mildly spicy kind made with napa cabbage, goes something like this: Salt the leaves to remove excess water; coat them with a mixture of aromatics (garlic, ginger, onion/scallion), shredded radishes and/or carrots, lots of gochugaru, maybe seafood seasonings such as fish sauce and/or saeujeot (fermented salted shrimp), and sometimes a paste of glutinous rice and water that binds it all together and encourages fermentation; tightly pack the coated cabbage into a sealed container; and leave it to ferment until it sours and softens a bit.
This is when the magic happens: The kimchi’s flavor undergoes a long and complex series of transformations, becoming more sharply sour at first, as sugar is converted to lactic acid, and gradually shifting into a funkier, more intense—but balanced—pickle as other flavor components evolve. At the same time, the cabbage’s cell walls break down and the once-crunchy leaves soften.
All those changes vary widely depending on the ambient climate during fermentation and how far into its life cycle—days, weeks, or months—you eat it. When it’s prepared according to traditional kimjang customs, fresh kimchi is packed into an earthenware crock called an onggi and buried in the ground.
“It will ferment all winter long,” explained Jeisook Thayer, who makes and sells kimchi on Martha’s Vineyard. She notes that burying the onggi prevents the contents from freezing. “You take out a little at a time, if you need to have it for that day or that meal.”
Nowadays, many Korean households are outfitted with a kimchi naengjanggo, a dedicated kimchi refrigerator with multiple zones that allows cooks to regulate the climate and produce batches with different levels of fermentation.
STAGES OF FERMENTATION
The following are commonly recognized (but not industry-regulated) stages of kimchi fermentation. Most stores don’t label the products as such (though some might indicate when the kimchi was made), and telling them apart is a matter of smelling or tasting them.
Geotjeori: fresh, unfermented, relatively crunchy kimchi that’s sweet and salad-like, with bright white cabbage
Kimchi: well-fermented, everyday kimchi
Shin Kimchi: overfermented and more acidic kimchi; often used in cooked dishes that incorporate kimchi, like kimchi bokkeumbap and kimchi guk
Mugeunji: fermented at a low temperature for at least six months so that it’s very pungent
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