As for game mechanics, I don't think +happiness would be optimal. For starters, happiness is damn near useless and once you invest a couple hundred units of stone on wall and floor tiles, it ceases to be a factor for the rest of the game.
I suggest: After eating (and only after eating), a dwarf looks for a beer barrel (not a table =) in close vicinity.
If one is found, the dwarf goes there, draws a mug full, and gains +energy from it.
I'm thinking of maybe 10-15% of a dwarf's energy bar. Not enough to fully replace beds. That's also why it would be limited to 1x after eating.
The beer drinking animation already exists so basically it would require ingame objects for various beer kegs or barrels... and a very localised addition to the AI which won't add any more performance issues because it's not part of the regular decision loop.