Weird carbonation issue bright tank versus kegs

[AnthonyB]

Should I expect to lose some amount of product carbonation after I fill a keg? I currently manually fill kegs by:

* Purging receiving keg with CO2 at 15psi
* Connect filling head to bright tank and turn on product flow
* Crack valve on gas connection of filling head, allow CO2 to bleed, beer to fill.

The whole process usually takes about 3 minutes to fill a 1/6 BBL of beer with no resulting foam. But I've begun to notice a difference in carbonation between beer left in the bright tank and the kegs. I test carbonation out of the tank and get 2.8-3 volumes depending on the beer. I test a recently filled keg and get the same. Last night I had the remainder of a keg come back from a special event and I tested it for the heck of it and got 2.4 volumes. I test another one that was filled at the same time but didn't leave the brewery, I get 2.8 volumes.

Any ideas? My next step might be to test on-site at a draft account.

[millerag]

Degassing

My first thought is that during transit co2 has come out of solution....then prior to tapping was relieved of the pressure to come down to serving pressure.

[Scott M]

What line pressure was the keg being pushed at, perhaps some CO2 boiled off at the beer fest. Especially, if a jockey box was used and the keg was at ambient. IOW, no worries...

[TL Services]

Is the account using mixed gas for dispense? If so, it is likely this is the cause of the reduction in CO2.

To maintain any gas in solution requires a pressure of that gas in the headspace of the keg. If the account is applying the correct pressure, but using mixed gas rather than 100% CO2, then the proportion of the total (ie. applied) pressure derived from the CO2 percentage in the mix will be lower than required for equilibrium, eg.

If you have a 100% carbonated beer (ie. no nitrogen) and you know it requires 15psi to maintain the level of CO2.
Applying 15psi of pure CO2 will be fine, as the pressure is 'all CO2'.
However, applying 15psi from a mixed gas (eg. 50:50 CO2:N2) then only 7.5psi will be 'CO2 pressure', and thus CO2 will come out of solution, lowering the amount left in the beer.

Hope that explains!

[AnthonyB]

Thanks for the responses. It sounds like as I continue my investigation that it is likely a combination of the serving conditions at the fest contributing to the low pressure keg coming back and a combination of conditions at a couple of the draft accounts where they aren't bumping up the PSI when they change kegs and put ours on.

[Larry Doyle]

Should I expect to lose some amount of product carbonation after I fill a keg? I currently manually fill kegs by:

* Purging receiving keg with CO2 at 15psi
* Connect filling head to bright tank and turn on product flow
* Crack valve on gas connection of filling head, allow CO2 to bleed, beer to fill.

The whole process usually takes about 3 minutes to fill a 1/6 BBL of beer with no resulting foam. But I've begun to notice a difference in carbonation between beer left in the bright tank and the kegs. I test carbonation out of the tank and get 2.8-3 volumes depending on the beer. I test a recently filled keg and get the same. Last night I had the remainder of a keg come back from a special event and I tested it for the heck of it and got 2.4 volumes. I test another one that was filled at the same time but didn't leave the brewery, I get 2.8 volumes.

Any ideas? My next step might be to test on-site at a draft account.

Is it a surprise that a used, partially filled keg has a lower pressure than a control keg? Would a half filled bottle have the same pressure as a full, companion bottle?