How long does opened kombucha last in the fridge?

The short version: an opened bottle of kombucha, kept cold and more or less sealed between pours, is usually still good to drink for about one to two months. That is a long window compared with most things covered on this site, and the reason is not luck — kombucha is already fermented and acidic before you ever open it, which is exactly the combination that makes a drink inhospitable to the bacteria that spoil milk or juice. What changes after opening is not really safety. It is fizz, sourness and flavour, and all three keep moving whether the bottle is open or not.

Why kombucha does not behave like an ordinary opened drink

Most drinks on this site get less safe the longer they sit open, because opening exposes a previously sealed, low-acid liquid to new bacteria for the first time. Kombucha is built the opposite way round. It starts as sweet tea, and a culture of yeast and bacteria — often shortened to a SCOBY — ferments it for days or weeks before it ever reaches a bottle, driving the pH down to somewhere around 2.5 to 3.5, similar territory to vinegar. That acidity is inhospitable to the pathogens that make most food-safety guidance nervous. Opening the bottle does not hand a clean slate of nutrients to anything dangerous; it just lets in a bit of air and lets some of the built-up carbonation escape.

What actually keeps changing

The honest way to think about kombucha is that fermentation never fully stops, it only slows down. In the fridge, the cold does not switch the culture off, it just makes it sluggish. Over the weeks after opening, three things drift in a fairly predictable direction: the drink gets a little more sour as remaining sugar keeps converting to acid, the carbonation gradually flattens because it is no longer trapped under a sealed cap, and the flavour mellows away from whatever fruit or botanical note the bottle was sold on. None of that is spoilage in the sense milk or meat spoils. It is more like the difference between a young wine and one that has had longer to develop — a matter of taste drifting, not a countdown to unsafe.

Raw versus pasteurised: the label distinction that actually matters here

Kombucha sold in shops splits into two genuinely different products, and the difference matters more than the printed date does. Raw or "living" kombucha still contains an active culture — it says so on the label, usually alongside "keep refrigerated" — and it keeps fermenting in your fridge the same way a home-brewed batch would, just slowly. Pasteurised kombucha has been heat-treated to stop fermentation, which is why it can sit unrefrigerated on a shelf before you buy it; once opened, it behaves closer to an ordinary bottled drink, without the ongoing sourness-and-fizz drift described above. If a bottle does not say which one it is, "keep refrigerated" on the label before you even opened it is the giveaway that it is the raw, still-active kind.

Home-brewed kombucha is its own category again — more variable than either, because it depends on how the batch was fermented and bottled, and it is worth judging on its own terms rather than by the timelines above.

What is normal, and what is worth stopping for

A few things people mistake for a problem are just the culture doing what it does. Thin, stringy, translucent strands floating in the bottle are cellulose and yeast from the culture, not a sign anything has gone wrong — many bottles list this as expected. A build-up of pressure under the cap, sometimes enough that it fizzes hard when opened, is the same ongoing fermentation making carbon dioxide with nowhere to go, which is also why an opened bottle should go back in the fridge promptly rather than sitting out.

What is worth paying attention to is different in kind, not degree: fuzzy or coloured mould on the surface, rather than the stringy strands described above, or a smell that has crossed from "vinegary" into something sharper and more chemical, closer to nail-polish remover than to sour tea. General food-safety guidance is consistent on this across categories — when something looks or smells clearly wrong in that way, the sensible move is not to taste-test to find out, the same "when in doubt" rule that applies to everything else on this site.

The habit that actually helps

Because the change is gradual rather than a hard cliff, the easiest way to lose track of an opened bottle is simply forgetting when you opened it — a half-finished bottle at the back of the fridge door is easy to overlook precisely because nothing about it looks urgent. Writing the day you opened it on the cap or the label turns "is this still the fizzy one or the flat one" into something you can just check, rather than something you have to taste your way into finding out.

This is exactly what Munch's opened-item tracking is for: marking a bottle as opened starts its own countdown from that day, separate from whatever date was printed on the label, and visible to everyone in the household rather than only to whoever opened it first — so the kombucha at the back of the door does not depend on anyone's memory of which Tuesday it was.