Why Kimchi Bubbles in the Jar

Open a jar of kimchi and it hisses. Bubbles climb the glass. Most people think it's gone bad. It's the opposite.

Nothing's carbonated in there. No one added fizz. So where are the bubbles in fermenting kimchi actually coming from — and should you be worried?

They come from living bacteria. Kimchi is packed with lactic acid bacteria — and a key group, like Leuconostoc, are 'gas-makers.' As they ferment the sugars in the cabbage, they don't just make acid — they release carbon dioxide as a byproduct. That gas forms bubbles that rise through the brine and build pressure in the jar. The more they ferment, the more gas, and the more sour it gets.

So those bubbles aren't rot — they're a progress bar. They're proof the bacteria are alive and working, turning your cabbage more sour by the hour. The fizz is fermentation, caught in the act.

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