The freezing point of beer depends on its alcohol content, but it generally freezes at around 28 degrees Fahrenheit. Beer is typically between 6 and 20 proof. For reference, 24 proof liquor freezes at 20 degrees, 64 proof liquor freezes at -23 degrees, and 84 proof liquor freezes at -30 degrees.
In practical terms, this means that most freezers are cold enough to freeze beer. The freezing point of ethanol, or drinking alcohol, is -173 degrees Fahrenheit, and the freezing point of water is 32 degrees Fahrenheit. The more alcohol a beverage has, the lower its freezing point is. Some stronger beers, such as barley wines and imperial stouts, are around 24 proof, but they still have a low enough alcohol content to freeze. Excessively old temperatures mask the flavors of good beer, so there is nothing to be gained from storing beer in the freezer.