From what I've read, cases of beer on board were not unheard of, but the rationing of such was controlled by the captain. A celebratory half-bottle per man would be typical.
EDIT: A few pages down in this interrogation report, you can see a list of the the provisions U-434 took on at Vigo. A case of beer, quite a few bottles of liquor and 2 cases of wine are amongst the supplies.
http://www.uboatarchive.net/U-434INT.htm