Here is my bottling process. Cold crash, keg, purge air, force carbonate while cold. Sit a few days while serving in the kegerator and the carbonation is fine. Time to bottle some to take to competition. Reused brown bottles are cleaned and sanitized with Star San. Using silver O2 absorbing caps are in a bowl of Star San. Using a cleaned and sanitized Blichmann beer gun, purge bottle of air, then dispense. Cap using the red two-handed capper. I store them cold. Within a few days however, the bottles are nearly flat. A BJCP judge explicitly mentioned that the sample was under carbonated. What could be the culprit for flat bottled beer?

3 Answers 3


Could be a couple things.

Make sure your capper isn't fatigued. Cripped caps shouldn't twist even with a rag and a good amount of force.

Using a beer gun can lose carbonation. The tale tale sign of one not set up right is more than 2 inches of head in the neck you have to flow out. Before the neck it should have almost no foam.

Serving pressure on a keg system should be 12-15 psi. If you dial down less than the psi you carbonated with, you will lose carbonation as the keg empties.

  • 1
    The capper is inexpensive and about 10 years old. I concur that is a possible concern. I'll check for twist-ability. For the beer gun, I fill to the top, then remove the beer gun which is purported to leave the perfect amount of head space (and is nicely consistent, too). We have fairly short beverage lines (3 ft / 1 meter), so the regulator is set to around 7 to 10PSI. I'll double check best practices on that.
    – Micah Epps
    Apr 20, 2018 at 13:48
  • 2
    We experimented with a different capper and found that to be the culprit. Thanks for all the help
    – Micah Epps
    May 4, 2018 at 11:55

I havn't used o2 absorbing caps, but here's what I've found out. You can check with your next batch to see if this was the problem: - If you sanitize the o2 caps, you lose the oxygen absorbing properties.

So check the caps. Do some normal caps, and some o2 caps, and some santised o2 caps. Those o2 caps when it touches liquid, it activates. SO when you santise it, you're activating the o2 absorbing part already.

I would also check to increase your force carbonation. Why? When you bottle it, there's extra head space in the bottle. Some co2 going to go out of the beer and into that space. You can also test with extra carbonation and see if that was a problem.

  • I didn't realize that about the O2 caps, thanks! And we have planned to do an experiment with some other styles of caps.
    – Micah Epps
    Apr 20, 2018 at 13:53
  • O2 caps need to be prewet to activate the cap, and the seal ring. Capping dry and tipping bottles isn't recommended to activate. Though soaking for a long time in starsan can degrade the seal. Much like the slime silicone tubing gets when left in for several hours. Apr 20, 2018 at 14:05

If your carbonation is fine check in a clean beer Glass, then fill the bottle but if make it look like a 17 year olds first date and foam.it up, that's where your carbonation is going.... Foam is full of co2 then when the bubbles subside u lose carbonation. Keep the foam down, low serving pressure

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.