Distillation by freezing

Hey guys!

I assume we all know how distillation works: You use the different boiling points of liquids to separate a mixture of them. I have a bottle of vodka in the freezer and was wondering why not the same is happpening in this case: The water should freeze and the alcohol should stay liquid... Ideas?

>>3
The point is that it is not frozen though. The mixture contains about 40 vol-% alcohol, the temperature in the freezer should be -15°C I guess. I thought it should freeze and by removing the ice that builds I could increase the relative alcohol content. Why does it not work?