I ran out of CO2 while force carbonating. I barely had enough to seal the lid and purge the air out. I plan on getting more CO2 tomorrow but I'm afraid the beer will absorb the CO2 in the corney keg lowering the pressure and the lid will unseal exposing the beer to air. Is this a valid concern?


2 Answers 2


No, it's quite alright. CO₂ is heavier than O₂, and it's a very constrained pathway for O₂ diffusion. For just one day, it's totally fine. Heck, it'd probably be fine for weeks, honestly; even just a couple of PSI is nothing to sneeze at.

  • Thank you, first time doing all this so of course I over think it.
    – Jordan
    Commented Dec 17, 2013 at 5:48
  • 1
    It's true that CO2 is more dense than air, so it can initially be poured as a layer (there are plenty of demos on the net showing CO2 putting out a flame). However, gasses immediately start to diffuse into their container - so it doesn't take long for CO2 to diffuse into the area that contains it, and it would escape a non-sealed keg and be replaced by air. If diffusion didn't occur, we'd all be walking in a layer of CO2 in our homes.
    – mdma
    Commented Dec 17, 2013 at 15:07

It will be fine for a day if it's cold. Your keg may even remain sealed without the pressure from the gas - some kegs seal on they're own (but not all.)

I had one keg lose pressure and was exposed to air for a couple of weeks - the main problem was loss of aroma, and then a little staling.

  • A keg that does not seal is faulty -- replace the o-rings, and if that doesn't fix it, replace the poppet valves and/or the pressure relief valve. I have found that when reassembling the poppet valves after cleaning, I need to be careful to seat them properly too. You should be able to fill an empty keg with 10psi of CO2, and find it still at 10psi weeks later.
    – jalynn2
    Commented Dec 17, 2013 at 18:42
  • I agree - although I'm not talking about leaking gas, I mean that some kegs can hold the lid in place without any additional pressure from gas needed, so that the seal is maintained even when the gas has dissolved into the beer and the pressure drops 20-fold.
    – mdma
    Commented Dec 17, 2013 at 19:43

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