No room to bring them inside. Thinking that leaving extra room for expansion, like 3/4 full carboys might be safe. Also considering wrapping in a tarp for insulation, and hoping the heat from fermentation will help... but then I'd have to catch just when that stops. Maybe someone who has freeze-distilled outside in a glass carboy might have a tip on survival chances of my carboy.

It is a cider/mead (cysor). Expected ABV 10%, already got 5%.

I'm not intending to freeze the cider, but I don't need to avoid it as far as I know -- except for the glass breaking potential.

Also have concerns about a 3/4 full carboy (for expansion room) and the associated surface area/oxygen access (expecially when fermentation slows/stops). But probably if it's too cold for booze production, vinegarization won't happen either.

Update: Made through our mild winter (it appears). Full Carboys had just the slightest ice on top, no risk of full freeze and therefore broken glass. I don't think it got colder than about -7C though. A half-full carboy of vinegar did get more freezing, and shook them to keep the ice moving and it was fine. Fermentation has resumed. Alls well.

  • 1
    The heat from fermentation is not a factor. Once the temperature drops below the yeast's operating range, fermentation will stop. Oct 30 '15 at 13:49
  • Are you sure it will freeze? Are you trying to make it freeze? If it does freeze, hopefully it's bottom to top, not the other way around. Either way, engine blocks open up like they had a zipper when the water inside freezes. Glass carboys shatter when you look at them funny... If you can't get them inside, drink them.
    – Pepi
    Oct 31 '15 at 11:30
  • see edited post re: I don't want it to freeze, but it's fine if it does.
    – Max
    Nov 1 '15 at 18:56
  • @pepi, can't drink that much that fast!
    – Max
    Nov 1 '15 at 18:58
  • @Max Not with that attitude! :)
    – Preston
    Nov 4 '15 at 8:34

The density of water at room temp is 0.998 g/cm^3. The density of ice is 0.9167 g/cm^3. Thus, one gallon of water very near the freezing point would create just about 1.09 gallons of ice.

The most important part of this operation will be making sure you have some mechanism to relieve the pressure that builds up as the cider approaches freezing. If you are using airlocks, make sure they don't freeze up. If that happens, best case is that the airlock gets pushed out of the carboy. Worst case scenario is that the carboy breaks.

I think it would be a stretch to say that the heat from fermentation would prevent some thing from freezing. I guess it just depends on how cold it gets where you live.

  • The more I think about this and after reading Molot's answer, I wouldn't even try it in glass. Go get a bucket.
    – BoilerBrad
    Oct 30 '15 at 11:50

No one can know for sure. It depends on too many factor to reliably guess.

The better insulation, the better chance that fermentation heat will be sufficient - for some time, at least. Alcohol contents helps, too. If your beer is at 5% ABV, freezing point is t about -2 C / 28 F. Sugar content may bring it further to -4, maybe even -10C, depending on your gravity. That's possibly low, but you don't know the exact point, and weather can get colder. So these factors only slows things down and lessens the risk a bit, but not prevent breakage.

Then, the slower freezing goes, the lesser chance for break. Again - thick insulation helps. And not only around, but also on the top, because top of your tank is when you lose most of your heat. Extra room is only useful if there is enough time to displace not yet frozen liquid up, and if the airlock is not yet frozen. Replace it with gauze or add a lot of salt to water to ensure it's freezing point is way below what you can really expect (saturated salt solution can have freezing point as low as -21 C - weather sometimes gets colder, all right, but it might be rare enough in your area).

And don't forget that once frozen, water ice expands still with drop of temperature, and then buffer space is of no use at all - it's solid now, it will expand equally in every direction. Glass, on the other hand, shrinks. So once layer of ice has thickness comparable to that of your glass, it's time to start to worry. Sometimes glass breaks first. Sometimes it's ice - but then, breaks in ice only open more space for new ice. At some point in time-temperature chart, glass will fail. Trying not to reach that point is a risky game, one I liked to play in winter, but with bottles I didn't care about, and water or other "school project" solutions, not something I care about, like my wort.

  • good stuff -- makes me think about some ice maintenance. If it freezes slowly, which it probably will, I can do some poking and make sure I have mobile ice, rather than a solid block. This would help relieve that pressure. At some point all that can freeze, will have. But might thaw and freeze again.
    – Max
    Nov 1 '15 at 19:02
  • @Max Good luck. But really, if possible go with plastic or wood. If this time it's impossible, slowing things down in hope it'll get warm before the crash might be the only way, but it does not make it a good way.
    – Mołot
    Nov 1 '15 at 19:22

Wrap the carboys with heating belts. I defiantly wouldn't let it freeze uncontrolled.

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