It's an understatement that beer is very popular in Boston. There are many pubs (Sunset Grill, Publick House, John Harvard's...) that survive on epicurean beer. Boston is a great place to visit if you want to try many different makes of beer. It is almost as big a sport as baseball here.
There are two popular beer brewery tours here: Sam Adams and Harpoon. I recommend both. The tours are very similar, but at Harpoon the tour guide has a microphone so you can be sure to hear him/her. At the end of each tour there is ample opportunity to sample different selections of beer, but at Sam Adams you have about 3 or 4 samples of beer that is pre-selected and you sit at benches with fellow tour participants. You have to wait for the beer to be served, so actually it is a good opportunity to talk with other people. By contrast at Harpoon you can ask for as many samples as you want at a bar-style sample counter with about 8 varieties straight from the tap. If you want to try them all, I don't recommend drinking a full glass of each! My favorite was a light, orange flavored UFO White.
Other recommendations: Go early, buy tickets ($5) for a tour later in the afternoon and in the meantime get a fresh seafood meal around the corner or even visit the nearby Children's or ICA Museum.
