pressure vs carbonation

I think I will finally admit to myself it was a mistake to have never taken a physics class in HS or college.

Question:

Just kegged 10 gal of beer into 2 cornies. One keg went into the kegerator on gas with 9lb CO2 while the I other pressurized with 20lb of CO2
and put into my garage for "cool storage" (ambient temp around 48F). After a week I pulled the pressure relief valve on the keg in the garage and got a whisper of a hiss. If I am sure the keg was pressure tight, what happened to the pressure?

I am guessing the 20lb of CO2 filled the void between the liquid and the lid. When the CO2 dissolved into the beer, the pressure equalized?

Or could it be the drop in temperature from 67F to 48F reduced the pressure in the keg as the liquid contracted?

Or a combo of both?

A combo of both.

A combo of both.

Click to expand...

True, but the decrease in volume of the liquid is completely negligible compared to the decrease in volume of the gas. Liquids for the most part are "incompressible." The main culprit is the beer absorbing the CO2.

If you want to store your beer without it being constantly hooked up to gas, you should keep giving it "hits" of CO2 (over a few days) until it stops absorbing and the keg retains pressure.

iceman has got it. Even the decrease in CO2 pressure in the head space from the temperature drop is negligible (not even 4% pressure drop). Also, liquid absorbs more CO2 at lower temperatures.