Bottling vs CO2 carbonation

[ersman]

I just started kegging about a month ago after about a year's hiatus from brewing because I really hate bottling. Makes me wonder why I didn't start sooner. I digress...

So, now I am interested in the basic chemistry / science behind the CO2. When bottling with priming sugar, after about a month the carbonation sets in. I can leave a bottle in storage for a long time without the carbonation ever going away. With CO2 on the other hand. If I were to fully carbonate a keg, then disconnect the keg from the CO2 tank, eventually the carbonation will go away. I keep hearing about how it eventually equalizes in the keg. I'm assuming this is what's happening, but I guess I can't wrap my head around how there can be a certain amount of pressure (30PSI for example) in a sealed container and eventually goes away if there isn't a constant pressure of the CO2 tank. Why doesn't it behave the same way as a bottle that is capped tightly with priming sugar? Thanks and I apologize for the bonehead question.

 

[sandyeggoxj]

If the carbonation in the keg is going away after the beer is fully carbonated to the desired volume then there is a leak in the system.

 

[smizak]

If I were to fully carbonate a keg, then disconnect the keg from the CO2 tank, eventually the carbonation will go away. I keep hearing about how it eventually equalizes in the keg. I'm assuming this is what's happening, but I guess I can't wrap my head around how there can be a certain amount of pressure (30PSI for example) in a sealed container and eventually goes away if there isn't a constant pressure of the CO2 tank. Why doesn't it behave the same way as a bottle that is capped tightly with priming sugar? Thanks and I apologize for the bonehead question.

What happens is that the beer absorbs the CO2. At different temperatures and pressures the beer has a maximum amount that can be dissolved in it. So eventually, the 30 PSI you talk about will stick, after the beer has absorbed all it can. It helps to understand "volumes of CO2" that you hear about. A typical beer carbonated at 2.5 volumes of CO2 means there are 2.5x the volume of the gas (CO2) dissolved in the beer as the size of the container(keg, bottle, etc..). The pressure required to do so changes with temperature. That is why you have your handy CO2 charts for kegging.

 

[mr_rogers]

If you leave the keg attached to the co2 tank UNTIL it equalizes then disconnect it will maintain the same pressure unless there is a leak. If you did connect it and it looses head pressure it's one of two reasons: 1 there is a leak in the keg seal that only becomes apparent when you disconnect it from the Co2 tank or 2 the Co2 head pressure is going down because the co2 is being forced into solution.

 

[ersman]

Thank you! Sorry, that was a poorly worded question and I didn't give all the details.

If, after the keg is fully carbonated in the refrigerator at 39 degrees, I shoot it with 30PSI, remove the CO2 AND move the keg to a warm corner in my house. After about 2 weeks, should I still have the 30 PSI with the temperature change?

 

[kombat]

+1, you've got a leak.

 

[Clonefan94]

Your keg is leaking more than likely. If a beer is fully carved and you take it off the gas, it's just like a giant bottle. Only way to lose co2 is to a leak somewhere. Right now I only have 3 taps but 4 kegs with beer in them. The one was off almost a month to age a little more (vanilla, chocolate porter) was still fully carbed when I plugged it back in.

So yeah, check the seals on your keg.


Sent from my iPhone using Home Brew

 

[smizak]

Thank you! Sorry, that was a poorly worded question and I didn't give all the details.

If, after the keg is fully carbonated in the refrigerator at 39 degrees, I shoot it with 30PSI, remove the CO2 AND move the keg to a warm corner in my house. After about 2 weeks, should I still have the 30 PSI with the temperature change?

No, you won't. The CO2 will dissolve and equalize at some volume determined by the temp of the warm spot. One shot of gas won't do it.

Carbonate your beer to the volume you want IN THE FRIDGE. Then store wherever. Put the beer back in the fridge, given the temp is the same as earlier, it will eventually equalize back at the initial volume of CO2

 

[sandyeggoxj]

No. The 30psi that you shot it with will dissolve into the beer and reach equilibrium. If the beer is fully carbonated at 39 degrees then just take it out of the kegerator. If the keg has no leaks then it will maintain that predetermined carbonation volume, lets say 2.5 volumes. That would put the keg at 11.8psi at 39ºF. If you raise the temperature to 70ºF the keg will be at 28.8psi, give or take. The pressure will change based on the temperature but the quantity of co2 will not change.

The same thing is happening with bottles. The pressure inside is changing based on the temperature but the specific quantity of co2 that is contained within the bottle stays constant.

This is all assuming there are no leaks. If that happens this all goes out the window.

 

[ersman]

This is great, everyone! Basically, the beer only equalizes when the temperature changes in the beer? Also, since bottles are conditioned at room temperature, the pressure also changes depending on the temperature prior to opening the bottle? Since cold beer absorbs the CO2 better than warm, the pressure will decrease?

 

[doug293cz]

This is great, everyone! Basically, the beer only equalizes when the temperature changes in the beer? Also, since bottles are conditioned at room temperature, the pressure also changes depending on the temperature prior to opening the bottle? Since cold beer absorbs the CO2 better than warm, the pressure will decrease?

Yes. The CO2 pressure in the headspace of a warm bottle is higher than the pressure in a cold bottle, even tho the amount of CO2 in the beer is almost the same (some had to come out of solution to increase the pressure.)