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Mixing CO2 with Air under pressure

  1. Jan 25, 2010 #1
    Hello folks - I hope this is the right area to post....

    I brew beer at home, and air, more correctly, the O2 in air causes oxidation and ruins beer. In order to prevent it, many home brewers use stainless steel containers that can be pressurised with CO2.

    The commonly accepted wisdom is that a squirt of CO2 is let into the container to pressurise it up to say 20 psi. A pressure release valve is then pulled to "expel air" dropping the pressure a little.

    My query is this - how does CO2 mix with air under pressure in the vessel? Does it form a layer underneath the O2 in "air" or do the two gasses mix. What is the explanation behind the answer?

    Hugely grateful to you for the answer, since I have been relatively uncomfortable with the explanation that the CO2 forms a "layer" to protect the beer. I personally don't think it's that simple surely?

    Thanks :)
  2. jcsd
  3. Jan 25, 2010 #2


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    Staff: Mentor

    Most likely they mix perfectly and all you can get with the procedure described is dilution (less O2 left, but it is still present). Repeat several times for best results.
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