It would be great if I didn't have to ruin a bottle of beer by opening it to test to see if it carbonated. Is there any way to tell?

  • 1
    had this problem myself once. Bought crappy bottles with grolsch style caps and some of them leaked. It would be great to be able to figure out if a particular bottle had leaked so I could recarbonate it and exchange the cap to something better.
    – Laserallan
    Dec 13, 2010 at 1:08
  • 14
    Ah the famous Schroedinger's Cap question :)
    – Tim Holt
    Dec 17, 2010 at 2:27

7 Answers 7


This is possible, but not in a scientifically measurable way.

Try this:

  1. Hold one of your bottles of beer up to the light so you can see the air gap that expands from the top of the bottle down to the top of the beer in the bottle.
  2. Quickly turn the bottle upside down then back again, with a slight amount of force, but no need to shake it.
  3. Observe the air gap in the bottle and notice the amount, if any, of bubbles forming at the top of the beer. If the beer is lighter in color, also notice the bubbles floating to the top.
  4. Through trial and error, I have found this method to be fairly accurate in predicting the level of carbonation in a bottle, but as I said, it's not something you can measure.

You can compare store bought beer bottles to get an idea of what to look for, but keep in mind that different styles yield different levels of carbonation.

  • awesome suggestion! I love it!
    – CLJ
    Mar 15, 2014 at 16:32

If you are that dire for things to happen quickly fill one plastic bottle each time you bottle. It will be firm once the beer is carbed. You can simply re-use 16-20oz soda bottles for this, or buy plastic beer bottles with screw on caps.

  • I had no clue that it was possible just to use plastic soda bottles. That is a good idea. My local home brew store does not carry plastic bottles, so this a good way to go. I'll definitely try this.
    – CLJ
    Dec 13, 2010 at 21:45
  • @CLJ: It really isn't an option for ALL of your homebrew. Everything I've read has said to avoid plastic as much as possible, let alone for the bottling/conditioning process. This is for two reasons: (1) plastic tends to scratch, leaving places for unwanted microbes to live and survive your sanitizing step, (2) the slow ramp up of pressure would likely cause the bottles to explode. My initial feeling is that the bottles would simply be impossible to sanitize the the degree required for an unspoiled beer, thus the "fill one" bottle statement.
    – EDWF
    Dec 15, 2010 at 17:27
  • brewchez may correct me if I'm wrong, but I think the point of the suggestion to fill one plastic bottle is to treat that bottle only as a gauge of carbonation, and to throw away the contents once you are satisfied that the batch is carbonated.
    – Ryan
    Dec 20, 2010 at 1:27
  • I've been using plastic better bottles for primary and secondary fermentation since I started homebrewing and I have yet to get an infection...I am an over-sanitizer with a spray bottle in my holster at every step. Plastic bottles of soda or water should be more than sufficient for this, and I don't think you'll need to dump it out either unless you have the habit of sticking sharp things inside the plastic bottle prior to filling it with beer.
    – Matthew
    Mar 6, 2014 at 22:08

A time test is your best bet.

Bottle carbonation should be pretty mechanical unless you're experimenting with conditioning yeasts. If you're not doing anything fancy with the carbonation, it should be safe to assume that your beer is done carbonating after two weeks.

  • 2
    yeah, but I don't want to wait that long...
    – CLJ
    Dec 12, 2010 at 23:53
  • 10
    @CLJ -- then homebrewing might not be the best hobby for you; patience is key
    – STW
    Dec 12, 2010 at 23:54
  • 2
    @CLJ- Start kegging if you can't wait for bottle conditioning.
    – brewchez
    Dec 13, 2010 at 12:25
  • 9
    @CLJ: brew more. Then when you're waiting for one batch to carb up you can drink your older batches. They key is to keep yourself waist deep in delicious beer!
    – JackSmith
    Dec 13, 2010 at 13:36

I usually wait a couple weeks then look for trub in the bottom of the bottle. If it's there, the yeast finished the job.

  • 3
    Wait a couple weeks - yes. But sediment at the bottom of the bottle only indicates that yeast have fallen out of suspension, and doesn't necessarily say anything about the carbonation. An uncarbonated bottle could have trub, and vice-versa.
    – Brandon
    Dec 13, 2010 at 21:34
  • However, no trub means you aren't bottle conditioning and should be able to know explicitly how much CO2 you put in. :)
    – EDWF
    Dec 15, 2010 at 17:33

I often open one after a few days, and then I'll often open one every day or two after that. I find it interesting to see how it changes in the 2-3 weeks while it's carbonating. How many bottles are in the batch? Is it a big deal if you lose a few before they were completely ready?

Another thing you can do is determine the carbonation level roughly by the noise and feel of removing the cap. If it seems under-carbonated, just immediately put on a new cap. That bottle will end up slightly less carbonated than it would have been if you'd left it alone, but the difference will be tiny.

  • I'm doing 5 gallon batches, so loosing one is not a big deal, but if I could prevent it, I would.
    – CLJ
    Dec 13, 2010 at 21:43

When I brew, I usually will do a number of mini bottles. Like the OP, I'm not one for patience. :) This allows me to have test bottles with minimal waste.


I combine the bubbles and yeast idea. Observation is a scientific approach. If you turn it upside down quickly and make some bubbles , there is definitely co2 released by the yeast. Oxygen alone may produce a little amount of bubles, but co2 bubles rushes up for a few seconds. You may notice a bit of this activity after the 1 week and it should be doubled in week 2. At the same time, even when the yeast at the bottom may only means the end of it's suspension it also means that the sugar frenzy was over and now yeast rest in peace. Also be patient and wait 2-3 weeks,that is part of the craftsmanship of making beer. Also, take notes of all the steps you've made during the process so you can share in a forum what you did exactly and by looking at the later you may also figure out what went wrong.

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