People often ask me, Dave, what the fuck is a sour beer? Well, if you stop swearing in front of my grandmother, I'll tell you. Sour beers are an old style of brewing fermented with bacterias. Typically brewed in the Flanders region of Belgium and often barrel aged, sour beers have more of a fruity, acidic bite to them. Almost vinegary. Some are even put through a second fermentation process with cherries or cherry juice to give even more tartness. Traditionally though, fruit isn't used. 
A very wine-like beer, Monk's Cafe flemish sour is my go to entry level for those in search of trying new beers. The most mild of tart and fruit, lightly carbonated and always refreshing. Found wherever a good import selection is had. Pair with more beer. Cheers and mahalo!

ps check out this euro dad saying some historic shit about Monks Flemish Ale.