Originally Posted by ajdelange
At room temperature 0.2 atm is going to give you about 8 mg/L. Thus pure oxygen at 1 atmosphere (open the bleed valve, put some O2 pressure on and let the O2 sweep out the air and then shut off the O2 and close the bleed valve) will result in about 40 mg/L. It might make more sense to pressurize to 2 atm (14.7 psig) with air as that gives a partial pressure of O2 of 0.4 atm and an equilibrium oxygen level of 16 mg/L.
But this isn't what they are asking. We want to know how much pressure O2 in a headspace is going to give us our total amount of O2 needed for the entire volume of beer. I think malfet is looking for an initial dose, that once shaken in (or left to absorb and diffuse), will result in the desired O2ppm... NOT the partial pressure of O2 that will give the desired ppm if the supply is unlimited, via a continuously connected tank/reg.
Yes, 8ppm at 0.2atm at equilibrium, but how much do we get from a given headspace to go into a given amount of wort at what pressure O2? Assume none goes into solution during the headspace charging....