Well, if we assume that any source of alcohol could be counted as beer, this device could be constructed by combining the water generator with a colony of modified algae (or an ecosystem of carb leaking algae and yeast) combined with some sort of membrane that allows alcohol through but not water. (Or a Brownian motion powered still).

That sounds pretty hard, but it would be a safe bet to say you could buy one within fifty years. Maybe longer if you want something nicer than pure ethanol.