This might sound like an oddball question. But does it make sense to add a small amount of sugar to a beer (after fermenting appears to have stopped in the primary fementer), after transferring to a secondary fermenter, to create a layer of CO2 right above the beer to keep oxygen out of it?

I had thought about getting a small tank of CO2, possibly even a paintball canister, to “top off” the jug, but a tiny bit of sugar would seem to be an easier way to achieve the same result (for the price of a small amount of additional sediment at the bottom).

Has anyone done this? Or does anyone have any opinions on this? Thanks.

  • I just noticed today (2 weeks in) that my 2 gallon jugs of beer are still cloudy because the yeast bed at the bottom keeps burping up CO2. A little chunk will rocket to the top, let out it's gas, then drift straight back down, leaving lots of straight little vertical trails. So I guess they're not done yet. So.. I think it would be safe to rack to a secondary, assuming the gravity is right, since there is still some slow yeast activity that should produce a small layer of CO2 on top in the secondary. Don't think I will add sugar. :)
    – Tim
    Dec 9, 2011 at 21:13

4 Answers 4


Well, no doubt it would create some CO2, but to answer your question directly, no, it doesn't really make sense. It's just not needed...and for that matter, secondary isn't needed most of the time. A better solution than adding sugar to the secondary is to just skip secondary entirely.

  • I agree; there's rarely a need to seconday.
    – sgwill
    Dec 7, 2011 at 19:59
  • Thanks for all the answers! I was mostly interested in using a secondary to help clear the beer, and I like the sanitized glass marbles idea. A while back I watched this couple on TintoTV use that method, so I may try that.
    – Tim
    Dec 9, 2011 at 16:32

Another way to reduce O2 exposure in the secondary is to reduce headspace. A smaller vessel is one way to do it. Winemakers apparently use sanitized marbles to displace the liquid and reduce headspace.

Edit: as a small aside, I've found beers will offgas more than a little CO2 during the transfer to secondary and subsequent movement. So even though your yeast is done doing its thing, you will most likely still have your CO2 security blanket.

  • 1
    Likewise, C02 trapped in the liquid from the fermentation activity will bubble up out of suspension when the beer warms. So if you ferment at 65F, and secondary at 70F, then you'll already have the C02 that comes out during the temp shift to protect your beer.
    – GHP
    Dec 6, 2011 at 19:33

If you want to purge the vessel with CO2, this is a great idea, i would personally do it prior to transferring any beer into the fermenter since CO2 is heavier than air.

Ideally you should be able to use a small amount of CO2 pressure to transfer the beer from one vessel to the other. This is something I have been looking into (using carboy caps) but haven't yet tested.


There is CO2 dissolved in the beer post fermentation. The act of racking the beer disturbs the fluid enough knocking that CO2 out of the beer. I challenge that you get a small blanket of CO2 anyway. Is it the same as purging with CO2? Probably not, but that's my story and I'm sticking to it.

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