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Re-occurring Air Bubble in Beer Lines

So recently (maybe since the weather has gotten colder) I have a strange new phenomon of an air bubble developing in my beer line near the disconnect. Last time it was in one line. This time it is in another line with a completely different keg.

I have checked all connections and even tightened them down as needed. This is getting pretty annoying as it is causing a burp when pouring my pints and creating a lot of foam in my glass.

Any suggestions?

EDIT: Now that I think about it this more. It started in my root beer line and has no corrected itself. However it has moved to both beer lines. The first is not hooked up currently now.

EDIT2: Bumping up. Really would like to get this figured out. Not it is happening again to both lines that are hooked up. Pulled off disconnects and cleaned. Tightened all lines and connections. Tried different serving pressure because of temp change. Nothing. Really stumped here.

Bumping up. See EDIT2. Thanks!

How quickly does the “bubble” show up? I get a few bubbles in my lines if they have been inactive for a few days. Probably CO2 coming out of solution in the lines. How is your system set up? kegerator, keezer, CO2 pressure, beer line length, tank location with respect to faucets, type of faucets, etc…? Cheers!!!

The bubble shows up right away. you can see little bubbles where the line connected to the faucet and the disconnect. Then after just a few minutes there will be a big bubble (approx 1") at the disconnect and then several little bubbles up by the faucet.

Set up is a kegerator. I have 5’ beer lines that run from keg to faucet. The faucets are mounted towards the top of the door to allow freezer door to open. The lines just hang loose in the fridge. Perlick faucets. Tank pressure is set to 8psi. Temp in the fridge is about 38F. Kegerator is in the garage so during the winter is chills down a bit. Weird thing is I’ve not had this problem in the past during the winter months.

Thanks for the help and Happy Holidays!

I wonder if you might have an obstruction in the out tube/poppet or you may have an air leak at the Post/Disconnect. You might try taking the keg out of the kegerator, releasing the pressure, loosening the lid a bit so pressure doesn’t build back up, remove the out post/poppet , inspect/clean/lube & reassemble, pressurize to ~30 psi to reseal the lid and give it a try again after it settles down. Cheers!!!

Check all your o-ring seals especially the ones under the dip tubes. Just a suggestion but 5 feet of tubing is to short, up it to 10 feet and increase your pressure to around 12psi.

I just picked up some keg o-ring kits. I have to believe this is it as I’ve changed all connections and made sure all are tight. I even hooked up to another line that does not have the problem with its current keg and had the same problem. Thanks for all the advice! This has been very frustrating as I really want to drink the beer in the keg that is having problems.

Ok so I replaced all the seals in the keg. Replaced the Teflon washer between disconnect and the hose. Still have the problem. I don’t have any keg lube as I’ve never needed it in the past. Could there be something wrong with how the faucet is sealing when turned off?

I’m absolutely stumped at this point.

Did you try changing out the disconnect?
Teflon between the disconnect and hose. My disconnects are either barbed or flared. Can you post a picture?

I just use the typical MFL disconnects for both gas and liquid. I have used a different disconnect, line and faucet and had the same issue. So something is telling me its in the Keg. I think I’m going to order some new poppets and see what that does.

So I borrowed a poppet from another keg and put it in this keg. Same issue. I’m ordering new posts and poppets. This is getting to the point where I’m wasting more beer in testing.

I can’t imagine it’s over carbed but I’ll try to take it off gas and see what happens.

I don’t think I completely understand the issue. Are you saying that as you are pouring you can see bubbes forming right where the line meets the disconnect, and over time these bubbles grow to push beer out of the way and leave a 1" long void? I have seen this behavior when I carbonate the beer at one pressure then serve at a lower pressure (i.e. overcarbonating). Over time the excess pressure in the beer comes out of solution (since the gauge pressure is below the saturation limit).

How did you carbonate the beer, shaking, high pressure, same pressure? If it is indeed overcarbonated you can try raising the gauge pressure and see if that makes the problem go away. Your pour is going to be foamy as hell with 5’ of line, but that’s a separate issue. The important thing to check is the line, if you can keep the big bubble from forming then it’s just a matter of bleeding excess pressure until the keg pressure = gauge pressure.

By the way, you should be setting your gauge to the right pressure for the fridge temp and style, at 38°F and a typical ale you want 2.5 volumes, which is 11-12 psi (link

). If you turn down the gauge pressure to make the pour less foamy, you’ll eventually be left with undercarbonated beer, and in the short term see the beverage line bubble like you are seeing now. The way to deal with foam in the pour is to get longer beer lines so that the beer pours slower, or use epoxy mixing tubes in the dip tube.

While I’m not ruling out that 5’ of beer line at 8 psi is not a/the problem. I’m not convinced since I’ve had this same setup for over a year with no issues. At this point I’m leaning towards over carbonated beer or a bad post on the keg. I’ve tried two different lines/disconnects/faucets on this keg with the same problem. I’ve used both lines on another keg with no problems.

My carbonation method is to hook up to gas at 30 psi for 2 days. Then release all gas from keg and put back at serving pressure, 8-10 psi for a few days before serving.

I’ve got the lines to hook up a 10’ line and see what that does. Currently I’ve released all CO2 from the keg and letting it sit for a few days to see if it will reduce carbonation. If that is not it I will put a 10’ line on it this weekend and report back.

What stumps me is the bubble forms almost within minutes by the disconnect. I can watch several bubbles go through the line from the faucet back to the disconnect.

I’m not by any means disregarding the beer line length suggestion as most of you have been doing this way longer and know much more than me. I’ve just never had this problem in the past so I’m completely stumped.

Thanks everyone! I appreciate all the helps!


I’m not suggesting the beer line length will fix the bubble issue. Like I said, if the bubbling goes away after you turn the gas pressure up, then the beer in the keg is probably carbonated higher than 8 psi @ 38°. So you can try turning up the pressure and see if it stops the bubbling. Where you will run into trouble is if you dispense at this higher pressure. 5’ of line is fine for 8 psi, but at 12 psi then it may not be enough and you could still see foam even if you have fixed the original cause.

I would tend to believe it’s a pressure level situation (CO2 coming out of solution in the line), as others are suggesting. The only clue that suggests otherwise is that you are seeing this gas in the line so soon after drawing a pour. So, if it’s not a pressure issue (gas coming out of solution), I would ask how is a gas finding it’s way into the line?

The line is pressurized, so any leak to atmosphere would result in beer coming out, not gas going in. Agree? So gas coming in would have to be under pressure. Only place I can think of would be the headspace of the keg. If a diptube o-ring wasn’t sealing completely, CO2 from the keg headspace could find it’s way directly into the beer line out. Also, the dip tube itself, if not allowing a good seal, could result in the same.

But as I said initially, this is only an idea if you can convince yourself it’s not a pressure issue. Good luck, and let us know what you discover.

Solved! Turns out it was over carbonated. Took it off gas for several days and released all a couple times a day. Hooked it back up yesterday and pours perfect. Now to solve how it got over carbed…

Thanks everyone! :cheers:

I’m hung up on the teflon washer at the disconnect, not that it is a root cause, but get rid of it if you are using standard MFL disconnects as you’ll notice the little plastic nub at the top of the threads that serves this purpose. It mat be nothing, but it creates another opportunity for a leak if not secure.

Next, your carbonation method has no controls and could be over-carbonating the beer. If you have over-carbonated beer being served at a lower pressure that doesn’t match the carbonation of the beer, that could be a formula for just the issue you are seeing. The C02 is coming out of solution in the lines because there is not a matching pressure to keep it in solution.

Make sure your storage temp and liquid temps are kept at 36-38f and don’t keep opening the door to look at those lines. C02 comes out of solution more rapidly as temps warm. Don’t fight physics.

Your line length is fine for 8psi, but most beers are not carbonated at 8psi. 10-12psi with 6-7 feet of line will make you a happier guy for a lot of different carbonation levels including your low carb offerings. It again is physics, don’t fight it. Unless this is a special low-carb style, carb to at least 10psi, keep it at 36-38f, and add a proper length line. Use 3/16" beverage line.

Lastly, as you are doing already, make sure there are no leaks in the system. If you have an intermittent leak it can cause issue and cost you a lot of C02.

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