Storing half empty kegs for a while .. over carbing issue

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Storing half empty kegs for a while .. over carbing issue

Postby lexuschris on Thu May 01, 2014 12:18 am

Hey all,

I've asked about this before, but was not very clear about my question. I'd like to take another stab at it. :)

After I've carbed up a keg of ale, and been drinking it for a bit, I sometimes need to put a new keg in the kegerator to force carb or serve, etc. So, I take the half empty keg out of the kegerator and put it in my den.

I presume the headspace of the beer would be whatever it was kegged at, when it was disconnected form the CO2. Presumably serving pressure of 5-10 PSI. As the beer warms to room temp, I expect that pressure would increase as the gas warms. I would also expect that the volumes of CO2 in suspension may slowly leave solution until an equilibrium is reached inside the keg.

What I keep finding is that when I put those half-empty kegs back on the tap after a few weeks/months, even after purging the headspace, the beer is very over carbonated. It seems that storing them under pressure at room temp increases the dissovled CO2 content... and I just can't get my head around why... or how best to prevent this.

Maybe I should just man-up and drink the rest of the keg before disconnecting, but in the interim, I am just releasing gas pressure as it warms, so that there is much less pressure in there while storing at room temp.

Any suggestions or thoughts?

A final example of why this matters to me... as I am getting my kegs ready to bring up to Lake Casitas this weekend, I don't want them to be foamy & over-carbed. So, once I disconnect them from CO2, do I need to purge the headspace of some pressure? Or is there something else going on here?

Thanks,
--LexusChris
"A woman drove me to drink, and I hadn't even the courtesy to thank her." – W.C. Fields
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Re: Storing half empty kegs for a while .. over carbing issu

Postby brahn on Thu May 01, 2014 10:50 am

Are you giving the keg time to cool down and let the gas that came out of solution time to go back into solution? I'll usually put the keg into the fridge and let it sit there for a day or so before hooking up the gas and that seems to work fine.

The only time I've seen the carbonation level increase when sitting at room temp is when you get another fermentation in the keg. It could be the yeast you used in primary or an infection. If it's an infection you should be able to taste it. You could take a gravity sample and compare to your previous FG reading to see if that's what happened. Make sure you degas the sample first.
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Re: Storing half empty kegs for a while .. over carbing issu

Postby jward on Mon May 05, 2014 5:00 pm

I'll put out an idea... When you raise the temperature of the closed keg the pressure of the CO2 in the head space will rise. This higher pressure will allow more CO2 to absorb in the beer. Of course, warmer liquid holds less CO2 as the same pressure. I expect the effect has mostly to do with how empty your keg is. The more empty the keg the more "volumes" of CO2 able to push into the beer due to the higher pressure. I have had over carbonated beer be a pain to get back down to reasonable levels. It's almost carne asada and margarita time or I would try to run the math and see if temp or pressure wins.
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