I've just finished preparing my first fermented drink ever (Kvass) and I used a Mason jar to store the preparation during the 2 days of the fermentation process as advised by the various guides I found. However I've come to realized after 10 minutes that the jar's rubber seal is in fact leaking carbon dioxide.

Is this detrimental to the final product, will it still be safe to drink ?

I have properly sterilized the jar itself (though it might not be required for the fermentation but rather for the conservation of the drink) and I don't really mind it not being very fizzy therefore I was wondering if it was still safe to drink it.

I don't have any other stronger sealable container at the moment that isn't made of plastic so I'll have to go with that.

  • Your question is? Please clarify. Plastic could be better than a Mason Jar.
    – Philippe
    Jul 23, 2018 at 14:32
  • But according to my sources, plastic bottles and fermented drink don't really mix that well. Also the question was already quite clear: "therefore I was wondering if it was still safe to drink it." but I've made it clearer. Jul 23, 2018 at 15:19
  • Edit your question instead of adding comments. Not all comments may be shown initially, and comment order is not always preserved.
    – Robert
    Jul 23, 2018 at 17:01

2 Answers 2


kvass made in such a way is generally safe to drink. Leaking CO2 does not usually cause any sanitary problems, just a decrease in carbonation of the drink. Kvass is generally enjoyed not very carbonated anyway.

  • Thank you very much, this is indeed very useful information ! Jul 23, 2018 at 15:15

Mason jars are not designed to hold pressure. They are designed to hold vacuum and burb pressure.

  • Like an airlock then?
    – Martin
    Jul 22, 2018 at 21:19
  • @Martin more like a burp valve. But you shouldnt try to carbonate in them in the off chance they do seal, a few psi would make a bomb. Jul 22, 2018 at 22:40
  • Is this detrimental to the final product or is it okay if it acts like a burp valve ? Jul 23, 2018 at 8:09
  • 1
    Not being pressure sealed is not detrimental to the final product. A lot of kvass is sold with only very mild carbonation from large "trailer tanks". If a more carbonated product is required then it is best to use screw top PE (fizzy drinks) bottles until the carbonation routine is confirmed. Jul 23, 2018 at 9:42

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