Serving pressure with tank in the keezer

So I just read a post with the pressure changes of a CO2 tank gauge related to the temp of thetank and I got to wondering... should we alter our serving pressures if we keep the tank in the keezer? Logic and science tells me that it is so with the ideal gas law (PV=nRT). I'm posting from my phone right now so I can't run through any calculations, but if I would normally serve at 12 psi out of the keezer, should I be serving lower with the tank inside?

High side and low side are totally different. No change.

Not entirely sure what you mean by that, but 1 volume of CO2 is 1 liter of CO2 in 1 liter of beer, and 1 liter of CO2 at 43F is not the same moles of gas at 75F, and really when we carb we're looking for an amount of CO2 in the beer which would only be able to be consistently/accurately measured by moles. Since the gas is denser at colder temp, you have more moles of CO2 in a given volume at 43F than at 75F, given that pressure is kept constant.

Pressure is pressure. If the pressure in the keg is at 10 PSI, the regulator outside the fridge will read 10 PSI too....

If the reg reads 10 PSI outside the fridge, the pressure inside the keg will be 10 PSI. Since carbonation is an equilibrium equation, you will get the carbonation that a calculator says you will get at fridge temp and 10 PSI.

Long story short, use your fridge temp for the carbonation chart/calculation, and don't worry that your reg is warmer than your keg.

Pressure changes with temperature. A keg at 65F and 18PSI will have about 2.0 vol. Volumes are your constant. At 40F, 2.0 volumes is equalized at 7PSI.

A great calculator is found at http://kotmf.com/tools/forcecarb.php.

Gremlyn1 said:

Not entirely sure what you mean by that, but 1 volume of CO2 is 1 liter of CO2 in 1 liter of beer, and 1 liter of CO2 at 43F is not the same moles of gas at 75F, and really when we carb we're looking for an amount of CO2 in the beer which would only be able to be consistently/accurately measured by moles. Since the gas is denser at colder temp, you have more moles of CO2 in a given volume at 43F than at 75F, given that pressure is kept constant.

Click to expand...

All true, but the keg, and therefor the gas in the headspace of the keg, is always at the temp of the kegerator. What does it then matter what the temp is on the high side (i.e. the tank)?

Mad_Milo said:

Pressure changes with temperature. A keg at 65F and 18PSI will have about 2.0 vol. Volumes are your constant. At 40F, 2.0 volumes is equalized at 7PSI.

Click to expand...

This isn't what he's saying. Of coruse you have to set your pressure for the temp of the beer. He's saying how teh Tanks HP reg will be un-readable do to lack of accuracy at the cold temp. The Guage on the LP side is what's he's questioning. as in, if it reads 10psi, is it only putting out 10psi or is that psi reading skewed because of the temperautre and actually putting out 12-14 (ie) psi.
I'm thinking the reg will be accurate and not affected by temp. It's still just reading the pressure coming through.
I have mine inside the fridge and use the settings the calcs say and get great pours. I think if this was a reality, we'd have brought it up already when we all had over pressurized beer.

No, the serving pressure stays the same because the beer temperature is the same.

However, when you put a tank and regulator in a kezzer, plan on having to adjust the regulator a couple times, as the mechanical parts work differently when cooled.

The density of gas will change with temp. but the amount of change is minimal. Liquids ability to hold CO2 in saturation changes immensely with temp changes

density of co2 at 12 psig
2.1529 kg / m3 at 32 deg f
2.1178 kg / m3 at 40 deg f
2.0015 kg / m3 at 68 deg f


For most people this would be of no concern as the change is too small