May 27 -- Spend time at a bar and you start to notice something: People are drinking a lot more bourbon. Revenues are up more than 40 percent since 2009 and, in an attempt to capitalize on this boom, the number of bourbon brands has exploded. It’s a great time for America’s only true native spirit, but in between the unscrewing of bottles and the clinking of ice cubes lies the potential for a hangover: A lot of the bourbon you see out there isn’t what it purports to be. Bloomberg's Sam Grobart reports.