[Stevie]

Maybe smaller volumes carbonate faster due to less volume for the co2 to dissolve into, but pressure is pressure. Container shape and volume doesn't matter as long as it can hold and maintain the pressure. The only situation where shape would matter is if it affects the surface area where the beer and headspace meet (keg on its side vs standing)

[tommymorris]

It definitely takes some fine tuning to get what works for your system. You know, all it takes is for your regulator and mine to be off a couple psi, or our temps to be off a couple degrees to have a noticeable difference. If you think about it (not counting shake method, don't like it), if a half full keg got overcarbed at a set pressure where the full one didn't, every keg of beer would get progressively overcarbed as we emptied it.

I think with a smaller volume the co2 dissolved in the liquid may reach equilibrium faster. I don't think the equilibrium changes with volume. Henry's Law is the relevant law. The volume of gas dissolved into the liquid depends on the pressure of the gas above the liquid and a constant related to the type of liquid. Henry's Law doesn't concern itself with the speed of reaching equilibrium. I wonder if that speed may depend on gauge pressure and the volume of liquid.

I don't know. I agree I need to find the right set point and time for my  system.

PS. I forgot temperature. Dissolution of gas in a liquid also depends on temperature.

[tommymorris]

I did some reading. I think Fick's law applies. This video describes diffusion of molecules into a volume.

https://www.khanacademy.org/science/health-and-medicine/respiratory-system/gas_exchange/v/fick-s-law-of-diffusion

The video talks about molecules diffusing through a wall. Fick's law is often applied to calculate diffusion rate through a membrane; such as oxygen through a cell wall. If the beer being carbonated is the volume then less beer is analogous to a thinner wall (smaller T from the video). 

In a keg, the surface area is the same. The pressure difference is the same. In both cases (5G vs 2.5G beer) the diffusion constant should be the same. But the thickness of the beer (height in the keg) is half as much for the 2.5G case.

As such, I think (I have no experimental data to prove it) the beer will reach equilibrium faster when there is less beer being carbonated. So, I think when boost carbing lower volumes you should either leave at high pressure for less time or not set the pressure as high.

[Footballandhops]

I try to stay ahead of schedule and simply natural carb in the keg with priming sugar...it only takes a week at room temp and I'm all set

[tommymorris]

I try to stay ahead of schedule and simply natural carb in the keg with priming sugar...it only takes a week at room temp and I'm all set

I have done that several times. It is pretty awesome. I added sugar. I guess from your comment you keg it a few gravity points before fermentation completes.

[Footballandhops]

I try to stay ahead of schedule and simply natural carb in the keg with priming sugar...it only takes a week at room temp and I'm all set

I have done that several times. It is pretty awesome. I added sugar. I guess from your comment you keg it a few gravity points before fermentation completes.

No, I wait until the beer is done and stable. Then I add 1/3 the amount of priming sugar needed for bottling to my keg, rack beer on top, seal with a good 30psi blast of co2 and just wait a week

It's the same principle as bottling your beer, I just like it better than force carbing by shaking because I find that I can hit my target carbonation level in a more predictable fashion