How much of the Havdallah wine should a person drink? If its less than a Reviis, should a Bracha Acahronah be made?
Essentially one has to drink male lugmav, (a cheek-full) in order to be yotza havdalah. Practically though, if he only drank that amount he will not be able to make a bracha achrona, because it is questionable if that is enough. Therefore he should drink a full revi’is, and then make an Al Hagefen.
M:B 296-6, Shulchan Aruch O:CH 190-3.