Beer is 90-95% water and it will expand when frozen, bursting open the bottle or can. Freezing beer can cause issues with carbonation and flavor, and the risk of broken glass or metal fragments means it is unsafe to drink a beer that exploded in the freezer.
Most homebrewers know the feeling of standing impatiently over the kitchen sink, waiting for a 5-gallon brew kettle to fill.
The molecules in water float around sort of randomly, forming and breaking loose hydrogen bonds. As water’s temperature lowers, those molecules slowly stop moving, eventually forming strong bonds that remain firmly in place.
Higher-alcohol beers will take longer to freeze than others. A 40oz bottle will, of course, take longer to freeze than a 12oz can.
A better, more worry-free way to quickly chill a beer is to place it in a bucket, pot, or cooler of salted ice water.
The different freezing points of water and alcohol will naturally cause the alcohol to separate from the rest of the beer.
Because freezing separates the alcohol, it is, theoretically, a way to extract concentrated ethanol. Though this may sound like a fun way to get drunk as quickly as possible, the taste and general experience of drinking this liquid are not fun and not recommended.