What happens when beer freezes?

The water freezes first (at least it did when this happened to me), leaving a plug of ice surrounded by a bunch of concentrated beer syrup. It might be fun to play around with this process to create stronger brews, in my case though it was undrinkable and I threw it out.

If your bottles don't explode, it won't make any difference. The CO2 will just dissolve back into the beer when it thaws. If you were letting the beer carb when they froze, it will take longer to finish. I end up freezing my beer frequently during the long Canadian winters.

That said, if you partially freeze your beer and syphon the liquid through the layer of ice, you'll be performing a form of distillation. This form of distillation is commonly used in the production of Eisbocks.

I often pop a bottled beer in the freezer for 10-15 mins to rapidly cool if I've forgotten to load the fridge. Problem is, sometimes I then forget. The next morning I find the cap has been forced off and there's a sticky mess. It seems the water content freezes and forces out all the sugar. Tasting the thawed liquid later, it's still bitter but with little sign of alcohol, so it looks like that gets forced out of the neck with the sugar.

Great question (+1)

I have never frozen beer so could not comment on flavour changes.

With regard to CO2, this should be unaffected as long as the beer is in a sealed container - hopefully one that does not split as the beer (90+ % water of course) freezes and expands.

As the temperature of a liquid drops the solubility of CO2 increases. The drop in temp will not cause the CO2 to come out of solution. Careful thawing should reveal that the beer is still carbonated and that the CO2 has remained in solution throughout.

It might be that, if the beer was in a sealed container that had a large 'air' space, the CO2 might come out of solution as the temperature dropped, on account that the pressure of gas above the liquid drops (contraction). My command of the physics is not enough to know whether the solubility increase has greater effect than the partial pressure drop above the liquid. For further reading look up Henry's Law.

I believe that freezing will cause a permanent haze, but I don't think it will harm the flavor in any significant way. As long as the bottles are sealed, all of the "stuff" that's in there will stay in there, so it shouldn't affect the CO₂.

did the bottles explode or pop the caps off? if not then you may be okay. I believe freezing will cause the CO2 to come out of solution but if the bottles didn't blow then it may go back a few weeks after they're thawed.

I'm not sure if freezing would affect the flavor or not.