Twenty-five years ago, a consultant-turned-entrepreneur began hawking a new beer to Boston bars out of a station wagon. Jim Koch hoped he could build a modest local business with a high-priced brew that was heavier on hops and malt than most domestic beers.

Boston Beer Co., the maker of Samuel Adams Boston Lager, is now a publicly traded company with a market capitalization of about $790 million. Mr. Koch, chairman of Boston Beer Co., has helped foster a revolution in small-batch American brewing.

Today,...