Sour beers, while they may have more history than any other beer style, are quickly emerging to becoming quite the trend here in America. I’m going to take a quick moment to briefly explain what makes a beer sour, and describe some of the more common styles of sour beer.

Hopefully you’ve read my Science of Yeast articles. In the second article, I explained the chemical equation for the fermentation of sugar into carbon dioxide and ethanol. The third article ended by briefly explaining the existence of wild yeasts and bacterias that are sometimes used in beer production. To put the two together: while the Saccharomyces strain of yeast will consume sugar and turn it into alcohol, there are other microscopic organisms that will consume proteins and nutrients and turn them into acid, typically lactic acid. Lactic acid is sour, as you should know if you’ve ever eaten plain yogurt.

American breweries that are making sour beers are typically adding very specific bacterias into their beer to produce lactic acid. The most common bacterias used for this process would be Pediococcus Damnosus and Lactobacillus Delbruckii. While this makes for an exacting, and nearly reproducible, product, traditional sour beers were never made this way…

Traditional Belgian lambics are one of the most fascinating styles of beer. Rather than adding a single and sterile strain of bacteria, they simply let the beer ferment spontaneously. That is, once the beer is brewed, the hot wort is transferred to a coolship in the attic. A coolship is basically a large, shallow pan that is left wide open. The windows in the cobweb filled attic are also left wide open, to allow the Belgian air to pour in and cool the hot wort. The beer is then transferred off into barrels and left to ferment. While the beer was left exposed overnight in the coolship, as many as a few hundred different strains of yeast and bacteria enter into the beer. This collection of living organisms will ferment and acidify the beer over the next several years. Due to the cornucopia of yeasts and bugs that are added to coolships, very few American sour beers can even come close to the complexity of a Belgian lambic (however it is worth mentioning that there are a couple American breweries who also spontaneously ferment their beers).

Once the lambics are stored in barrels, the brewers will then age these beers for several years, occasionally offering different vintages for sale. The younger lambics have a sharp sourness to them. As they age, they stay sour, however they become balanced out with the other phenols and esters that are produced by the various yeasts present in the beer.

Guezue is the holy grail of sour beers. A gueuze is a beer made by blending one year, two year, and three year old lambics together. This creates a beer that not only features the sharp sourness of a fresh lambic, but also the smoothness of an aged lambic. Guezue is one of the most complex beers that I have ever tasted, with different layers of flavors present in each sip.

As I’m writing this, I’m drinking an Oude Gueuze Tilquin à I’Ancienne. The aroma is like smelling a grapefruit peel, with a bit of an added mustiness, and a slight wood like aroma. The initial up front flavor is mix of various citrus fruits, like grapefruit, lemon, and lime, but it then fades and reveals various other fruits as well. Fruits like green apples, and berries like tart cherry become more present towards the finish. The beer has a champagne like carbonation and it gives the beer a dry and crisp finish. The finish shows off it’s musty, barnyard like qualities that fade into a lingering sweetness that resembles the sweetness in an orange.

I fully admit that the first time you try a sour beer, you may not like it. It is difficult to prepare yourself for something like it. The first time I had New Belgium’s La Folie, I had a difficult time finishing it. Now I can’t get enough. Like most things in life, it is an acquired taste. However once you acquire it, you can never let it go! Gueuze, though hard to find in Las Vegas, are a good start since they are a bit balanced in their flavor. Jolly Pumpkin makes several approachable sour beers as well. Something like Bam Bière isn’t exactly sour, more so a little tart. This will start to build your tolerance and acceptance for acidity in beer. Work your way up to something like La Folie. It’s a deliciously complex beer, but it is intense in it’s sourness!