I was perusing a question about uses for flat beer ("Are there any good uses for beer that has sat in my growler for too long?") when I came across an answer that mentioned "any use that doesn't require it to be carbonated would be fitting".

If I have flat beer, and I have, say, a sodastream (or some such), can I effectively re-carbonate my beer? What would be the disadvantage to doing so?

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    Two very good answers with little overlap...they're both the prettiest girl at the ball... :) – Jeromy French Jan 30 '14 at 17:49
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    cook with it! Sauer Kraut with beer. – Brian Mar 31 '17 at 6:33

Sodastream: maybe, but at your own risk.

According to Sodastream's FAQ, "You risk damaging your soda maker, not to mention making a big fizzy mess!". However, there are a few articles discussing how to carbonate non-water with one.

Anecdotes vary:

Some tips:

  • It will definitely void your warranty
  • Use plastic, not glass, bottles to avoid shrapnel if you make a mistake.
  • Take your time; most reports indicate it's easy to over-carbonate your beer.
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    It does work. I have done it. – Ken Graham May 26 '19 at 22:38

Add sugar to bottle-conditioned beer

Warning: This method is error-prone, high-effort, and probably not worth your time. Could be fun, though. :)

Most commercial beer is force-carbonated. That is to say, the beer is produced and ready to drink (minus the fizz) before they put it in the bottle and mechanically carbonate the beer.

Beer that is bottle-conditioned or bottle-fermented, however, is put into a bottle with some extra sugar. The beer is intentionally left with a little of the yeast from the fermentation process, and is sealed with the sugar. The yeast then does it's normal thing: it eats the sugar and excretes alcohol plus carbon-dioxide. Since the bottle is sealed, the CO2 has nowhere to go, so it goes into dissolution in the beer, giving you that fizz. Most bottled homebrew will be like this.

So, if you have a beer that is both flat and was bottle-conditioned (and therefore still has some yeast in it), you might be able to bottle-ferment it again:

  1. Add a very small amount of sugar to the bottle. Table sugar works, although corn sugar (which you can find from a brew store) is ideal. It'll be really hard to get the right amount (about 0.083 oz), so I recommend pre-measured tablets of the stuff: http://www.northernbrewer.com/shop/munton-s-carb-tabs.html
  2. Seal the bottle somehow. If you have a bottle-capper and some caps, that'd be ideal. Otherwise, you might be able to get by with a soda bottle and cap. If you're really lucky, your beer is in a swing top bottle.
  3. Wait a week, maybe a couple to be sure.

If you're lucky, there's enough viable yeast in the bottle to start acting again (now that it has new sugar to eat), which will create more CO2 and recarbonate the bottle.

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    I would add that you must use bottles that are designed to take the pressure (which can be more than exists in the finished product) if you do this. Growlers are not designed to do so and may explode. – user505255 Jan 30 '14 at 0:41
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    Also the right temperature would be important for the yeast to work. – pabouk Feb 1 '14 at 16:34

Yes and No. Yes you can re-carbonate beer either by injecting CO2 into it either with a Sodastream (are those things still around) or natural conditioning as mentioned in another answer.

No, you really don't want to do this. If the beer has gone flat, it is likely that it has lost the protective layer from the CO2 and oxidation has occurred and the beer is likely stale.

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Yes, you can re-carbonate long flat beer. If the beer has been only gone flat. Once re-carbonated I doubt that you would be able to tell the difference. I did this once with Corni Kegs and a CO2 pressure system over a couple days for 10 gallons. Tasted great. Beer doesn't go stale without contamination, but will go flat without a seal to keep pressurized. Next I am going to try to to rejuvenate a Growler from a microbrewery that I didn't screw the cap on tightly. This time, however, I will be using 2 ltr bottles, baking soda and vinegar!

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    Baking soda and vinegar? Care to elaborate? – Deep Ellum Dan Jul 18 '18 at 7:22

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