Why does a bottle of beer go from a liquid to a solid if open after
being left in the freezer for a while?

Here you go. Try this discussion of the same question, from last year:

http://ask.metafilter.com/mefi/19465

why?
because beer contains a lot of water. water freezes below 0 degrees
celcius. beer will freeze below 0 degrees because compounds like
alcohol, hop etc are dissolved and they lower the freeze point.Even if
you do not open the bottle of beer it will freeze, but carbondioxide
gas wil add to the lowering of the freezing point. Because ice need
more volume than water a closed beer bottle will likely crack.
experimenting with beer like this is to my opinion alcohol abuse :)
The best way is to drink it. cheers
Prof Kees

I LWys thought opening bottle or the can reduces the pressure and
hence elevates the freezing point.
Under pressure water's freezing point.

I always thought opening bottle or the can reduces the pressure and
hence elevates the freezing point.
Under pressure water's freezing point is lower and related to pressure.