Basic Physics ?

[Scooba]

So I'm still relatively new at kegging. I have 4 on tap as we speak. All have been forced carbed around 12-13 PSI and the serving pressure has stayed the same.

I'm just trying to get a grasp on the physics part and CO2 absorption. My understanding is the once the beer has absorbed CO2 and is fully saturated at the dialed in pressure, the the same pressure needs to be applied to keep it carbed up. I.E., serving pressure has to be the same. OR, does it not matter what the serving pressure is because once the beer is saturated with the correct volumes of CO2, it has nothing to do with serving pressure?

Please clarify for me!!!

 

[Punx Clever]

The pressure you keep the keg at determines how much CO2 is in the beer. Lower the pressure, the beer will off-gas CO2. Increase the pressure, CO2 will be absorbed.

Same thing happens when you open a bottle of Coke. Pressure drops, CO2 comes out of solution.

 

[Seven]

My understanding is the once the beer has absorbed CO2 and is fully saturated at the dialed in pressure, the the same pressure needs to be applied to keep it carbed up. I.E., serving pressure has to be the same.

This is correct. In order to maintain the desired carbonation level in the beer you must keep the same pressure applied at all times. Carbing the beer then changing the regulator setting to a lower "serving pressure" will cause the C02 to come out of solution and the beer will de-carbonate until it matches the new PSI setting on the regulator.

 

[stratslinger]

Basically, you're looking to reach an equilibrium point between the gas pressure coming off your regulator and the vapor pressure released from your beer. So, once you get the beer carbed to the desired level, you need to maintain serving pressure from your regulator, or the vapor pressure will overwhelm it and allow the gas to escape the beer and the beer will go flat over time.

 

[Scooba]

Thanks to all of you for the insight. This is what I thought. I have some gas law experience and this is what I was thinking. Appreciate it!!

 

[spokaniac]

It gets confusing/frustrating to some because it is not instantaneous. It can take several days for the beer to reach equilibrium with your regulator so your beer can go from undercarbed, to perfect, to overcarbed over the course of a few days without changing your pressure. But if you go by the charts for your serving pressure you will get there.