According to NPR, beer freezes at about 13 degrees Fahrenheit. Popular Science indicates that the water component of beer freezes at 32 degrees, but the alcohol remains liquid until the temperature drops very low.
NPR states that, as a bottle of beer freezes, it becomes slushy. The frozen liquid expands, and the ice beer sometimes forces the caps off of bottles. In other cases, the bottles crack and splinter. Popular Science describes how beer is occasionally partially frozen to make it stronger. Through the process of fractional freezing, some of the water is frozen, with the remaining beer poured into another container. This liquid contains less water, so it has a higher alcohol content than the original beer.