How to fix an under-carbonated beer

I recently opened up a couple bottles of my latest beer, and I notice that they're quite under-carbonated. Not flat, but definitely under-carbonated.

The beer (from a pre-hopped kit) has been in the bottle for 3 weeks, and that's normally enough time.

Can I fix this batch by opening all the bottles, adding some carb drops and recapping?

Was it a high-gravity beer?

No. 1.040.

is it a coopers pre-hopped kit?

Muntons...same thing.

Before just adding more sugar, do you know what went wrong? How did you prime before, and what was the temperature where the bottles were stored?

3 weeks at 70+ degrees F is a standard minimum for expecting an average beer to be carbed. Some will just take longer for no reason. If you were at a cooler temp, then you can expect them to take longer as well.

Keep 'em warm and give them more time before even THINKING about doing anything to them yet.

And don't drop carb tabs into a bottle with little carbonation unless they are cold. I'm in the process of fixing undercarbed beer now and it make one hell of a mess unless the bottles are cold.

Check your caps to see if they are on tight. If you can twist them a bit, the CO2 can leak out

+1 to the cats comments. I would suggest simpky giving them a little more time at a slightly warmed temp (70ish). Dont shake them but turning them upside down amd then rightside up, just to get the yeast back into suspension sems to help a little as well.

Thanks for the responses guys. I used 3/4 cup of corn sugar in the bottling bucket to prime.

1. I'm using Grolsch flip-top bottles that I've used before with no problem.
2. I've let the bottles sit at between 70 and 75ºF for 3 weeks now.

I'll wait another week before I try another one, then I should chill them before adding the carb drops?

No. The carb drops just add sugar, according to my understanding. You already put the 3/4 cup in there, assuming it's a 5 gal batch.

The seals on flip-tops eventually soften up and allow gas to escape under pressure. This has not happened to me yet, because I just started using them a year ago. Flip-Top says the gaskets are only good for 5 uses. How many times have you used yours?


Like others said, if it was 'kind of' carbonated, and you know for a fact you added 3/4c sugar, that means the yeast is still working, leave it alone, try flipping the bottles around to resuspend yeast that is sitting on the bottom.


You DO have yeast sediment on the bottom, don't you?

Just an update...I agitated the bottles and increased the temperature. After another week, the beer finally carbed up.