When performing a secondary fermentation, it's recommended to use a glass carboy rather than a plastic bucket, with one of the main reasons being that it reduces head space so that less oxygen is sealed up with the beer. If that's the goal, could you instead line a sanitized bucket with a sanitized food-grade plastic bag, siphon the beer into the bag, then seal the bag so that there isn't any head space at all?

BYO mentions lining a bucket with a plastic bag to help with sanitation, and assuming the bag is BPA-free, food grade, etc - would this be safe or at all effective?

  • 2
    Sealing the bag is a bad idea in case there is some residual fermentation that may go on. If the bag springs a leak, then you'd better had sanitized the bucket and the exterior of the bag.
    – brewchez
    Commented Mar 31, 2016 at 21:33

4 Answers 4


Oxygen in beer has to do with shelf life. A small amount of headspace is not going to effect the beer short term. I have secondary fermented plenty of 5 gallon batches in a 6.5 gallon fermenter with great results. I personally wouldn't go through the trouble of a bag liner especially if you are going to drink the beer within a couple months.


Or, use a carboy as stated in the original post. Anytime I have beer sitting for more than 2-3 wks, I use a glass carboy. buckets are for primary and quick turn arounds.

sealing in a bag will restrict CO2 off-gassing. Airlocks are designed to let air out and keep air out. the bag will restrict one side of this equation.

  • Using a carboy only fixes the issue if you've got enough beer to fill it, any smaller batches will leave the carboy filled with oxygen just like a bucket. Restricting C02 is a good point though. Commented Apr 1, 2016 at 13:00
  • Good point on restricting the air space with enough beer. I have always understood that the CO2 off gasses pushes the O out of the airlock filing the air space with CO2. The benefit of using a carboy is that you can see your fermenting wort without disturbing the air space. We have to lift the bucket lid to check the fermentation process in a bucket, whereby exposing the airspace letting CO2 out and O in.
    – Ryan Whitt
    Commented Apr 1, 2016 at 13:43

Sure. Wasteful, but it'll work just as you expect.

  • Assuming the OP can sanitize the bag effectively. Commented Mar 31, 2016 at 20:16

This would work but it is not safe. As all brewers should know ALL equipment needs to be clean and sanitized. It would be hard to clean and sanitize a plastic bad so therefore it is not safe. Although I have never tried this before that is the biggest problem I can see. The second problem is that it is very very wasteful.

  • The bags cost about $0.50 a piece, which isn't much when spending $50 for everything else in a batch. The bags are sold for food storage, so I'd hope they're already clean - soak them in sanitizer before moving the beer into it and there shouldn't be any sanitation issues at all. Commented Apr 1, 2016 at 12:58

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