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Where does the CO2 go?

Hi all, first post. I am trying to figure out where my Co2 is going when force carbonating. So, bring the keg to ~40 det f and hit it with 40 psi Co2, give it a good shake and wait. The next day, the pressure drops significantly. I am trying to figure out why. Volume hasn’t changed. Check, beer is now carbonated- some.
Thanks FE1

it’s gone from on top of the beer to in the beer.

Thanks Shizzy, I’m tracking so far. But, why does the pressure drop? Still there, right?

Slowly wrapping my head around it. It is gas compression not fluid. I’m learning. Thanks!

The pressure drops because the pressure value you are reading is the pressure of the CO2 gas above the surface of the liquid. It decreases because a portion of the CO2 you introduce into the keg has become dissolved in the liquid beer leaving less CO2 volume in the head space. This dissolved CO2 has created a mild carbonic acid solution. When its pressure is relieved (when you dispense and serve the beer) the weak carbonic acid solution (your beer in a glass) will not stay in solution under the lower atmospheric pressure. The bonds of the carbonic acid release liberating the CO2 and providing you with a foamy, carbonated glass of beer.

Thank you BrianH, I have been puzzling over this most of the afternoon. The obvious next question, and this my be the wrong forum, is: is there a limit? When will the gas stop dissolving in the solution?

Regards, fe1

The gas will stop dissolving into the beer depending on what ever you have the regulator set at.

If you have the regulator set to 12psi, it will equalize out at 12psi. Depending on the temp of the beer, you will reach various levels of “volumes of CO2” in the beer.

So at 50* and 12psi, you will have ~2vol of CO2. Good for stouts/porters. Not as good for IPA’s.

At 40* and 12spi, you will have ~2.5vol of CO2. Good for most beers.

Your maximum limit is the pressure rating of the vessel. Which is usually 130psi on corney kegs.

Because we are talking abut kegging, the draft section of the site would be the appropriate area to discuss this. :wink:


This is why you need gas to push the beer out of a full keg, while one with 3gal in it has enough head space (and pressure held in said space) to push beer out for a couple of days.

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