Sour Beer
Core styles: Gueuze, Flanders Red, Oud Bruin, Gose and Berliner Weisse
Sour beers have a long and interesting history; predating all other modern styles, it is said (arguably) that all beers were once sour beers due to the unknown presence of wild yeast in barrels and fermenters. This was a time before the discovery of yeast, a time before pasteurisation and a time long before the shiny, squeaky clean breweries that exist today. All the mainstream versions of sour beer we have today originated in either Germany or Belgium, and each country produced its' own distinctive styles that could be based around three desirable bacteria and one wild yeast: lactobacillus (clean, citrusy tartness), pediococcus (clean tartness with funky sourness), acetobacter (sour vinegar) and Brettanomyces (dry, funky, horseblanket). You may be forgiven for thinking that some of those flavour profiles do not sound particularly attractive but, when given the right platform to shine on they, really are delicious; perfect for a hot summers day even!
Belgium has a long history of doing strange and wonderful things with sour beer. The main styles hailing from Belgium are Gueuze, Lambic/Kriek, Flanders Red and Oud Bruin. Gueuze and Lambic are particularly interesting as they undergo spontaneous open-fermentation. Flanders Red and Oud Bruin are not spontaneously fermented, but they are often blended sours, which both have additions of lactobacillus and acetobacter to give them their signature tartness. The main difference is the colour and the aging process, Flanders Reds are aged in Burgundy barrels and Oud Bruins are aged in stainless steel fermenters.
Germany's contribution to the sour landscape is Berliner Weisse and Gose, both are similar beers which include the addition of salt and lactobacillus to add that sour, tangy funk.
Nowadays there are plenty of modern breweries taking up the sour torch so the days of limited production and rarity are long gone. Great entry points are Magic Rock's Salty Kiss, Siren Craft Brew's Calypso, Rodenbach Grand Cru for the wine aficionado and Timmermans Kriek if you fancy something fruity.
Admittedly, these styles can be a bit of an acquired taste. Yet, the fruit lambics from the likes of Lindeman's are an easier starting point into the world of funk or, if you're looking for something UK based, Wild Beer Co deal almost exclusively in weird and interesting sours.