I bought some pasteurized cider from a grocery store that was sourced from a local apple farm. The jug has been sitting in my refrigerator unopened since I got it.

To my surprise, after a few weeks the jug significantly swelled up, indicating that fermentation had occurred. I was definitely surprised by this since it was pasteurized, unopened, and refrigerated the entire time.

Is this safe to drink? Can I continue to let it ferment (maybe even at room temperature)?

I know most people add their own yeast so I am a little skeptical as to how safe this "mystery" culture might be.

1 Answer 1


More than likely- it's safe to drink. Pasteurization is really difficult to get right, especially for smaller farms.

You can of course leave it to ferment- and it clearly will continue to do so even when cold. Are you going to get a very drinkable cider? Possibly.

Depending on the strain of yeast causing the fermentation, letting the product completely ferment you'll likely get 1 of 3 things:

  1. Vinegar
  2. Low ABV cider that is pretty sweet
  3. Higher ABV cider that is very dry

Typically with wild yeasts you'll get 1 or 2.

Either way make sure you open the cap and bleed out the pressure once or twice a day (or get an airlock) otherwise the pressure will build and rupture making quite a mess in your fridge!

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