Time it takes for co2 to settle??

[mwsenoj]

When trying to purge a vessel of oxygen we often fill it with CO2 because CO2 is heavier and the oxygen will form a blanket on top of the CO2 and be pushed out. How long does it take before the CO2 and oxygen completely separate? I'm sure there's some sort of mixing going on so I want to put enough CO2 in and wait long enough so that my keg is completely purged of O2. Anybody with any scientific information on this question?

 

[doug293cz]

CO2 will not "settle out." That's not the way gas diffusion works. Two gases will eventually homogenize, not separate. The larger the difference in gas densities, the longer the mixing will take.

Brew on

 

[fj605]

The best you can do is to fill the keg with CO2, purge, fill with CO2, purge, etc. This will lower the concentration of O2.

 

[PlinyTheMiddleAged]

Doug is right. Gases don't settle - they will mix thoroughly. Check out this video. They start with separated gases (bromine and air - bromine is about 7 times more dense than air) and the gases mix in about 30 minutes.

http://youtu.be/_oLPBnhOCjM

The suggestion to pressurize with CO2, vent, repeat works through diluting the air in the keg - add CO2, vent air and CO2, add CO2, vent air and CO2,...

Another way to minimize O2 exposure is to fill your keg with sanitizer, hook up the CO2, and empty the keg. Now you have a keg full of CO2. Disconnect the CO2, then fill through the liquid in post while occasionally relieving pressure so the beer can flow in. I hope that makes sense!