While IPAs still top the charts as the most popular beer style in the US, there is little doubt that sour beers are the up and coming genre of beer. Rare on this side of the pond only a few years ago, craft breweries large and small are now cranking out amazing sour beers. Sour imports from Europe - especially Belgium - are arriving in record numbers and supply is not keeping up with demand. In this post, we will take a high-level look at the range of sour beers. In future posts, we will focus on specific styles of sours.

What are Sour Beers and Why Are They So Popular?

Sour - or high-acid beers - actually go back hundreds of years with origins in Belgium, Germany and England. What gives them their distinct tart flavors and complexity are various combinations of wild yeasts and beneficial bacteria strains. 

Hops were not always the dominant flavoring agent of beer that they are today. The brewer needed something to offset the sweetness of the malt in their beers. Blends of bitter herbs, called gruit, were used to that purpose. Gruit often contained hops and eventually hops replaced the other bitter herbs. But, some Belgian and German brewers learned how to sour their beers, which also served to offset the sweetness of the malt. Because sour beers are labor-intensive and require long maturation times, they remained regional specialties - until recently. 

A Wealth of Microflora

Most beers are fermented with pure strains of brewers yeast and brewers go to great lengths to keep those strains pure. Sour beers, on the other hand, rely on wild yeasts and bacteria for fermentation. These microorganisms give sour beers their distinct tartness, funkiness and complexity. Where do these microorganisms come from? They are in the air everywhere - especially during the summer months. Go into a vineyard. The white powdery stuff on the grapes is wild yeast. It's actually hard to find any place on earth that does not have colonies of wild yeast and bacteria in abundance. In the days before brewers understood yeast, bacteria and microorganisms in general, they didn't have to seek out wild microflora; the microflora found the beer. Probably the only thing that kept the wild stuff from souring all beers was the fact that the tartness and funkiness take a while to develop and most beers were consumed young.

Sour beers get their tartness from strains of lactic bacteria - predominately Lactobacillus delbrueckii and Pediococcus cerevisiae. They get their barnyard funk from various strains of Brettanomyces yeast, often referred to as "brett." In addition to these, many sours contain other microflora as well. In Belgian Lambic breweries, great care is taken to not disturb the environment of the brewery for fear that the unique combination of microflora might be altered or lost altogether, thus changing the unique personality of that brewery's beers. 

Brewing Sour Beers

Sour beers are brewed pretty much like regular beers - with various malted and unmalted grains, water, hops and yeast. The magic happens during extended fermentation. After primary fermentation, during which most of the beer's fermentable sugars are metabolized by the yeast, wild yeasts and bacteria continue to feed on trace sugars, proteins and any other nutrients to be found in the beer. This nutrient-poor environment stresses these microorganisms, causing the production of various compounds that give the beer its tartness and funkiness. This is a slow process that can take from 18 to 36 months, although modern brewers use various techniques like kettle souring and special yeast/bacteria strains to speed up the souring process. 

Sour beer fermentation takes place in stainless fermenters or, more traditionally, oak barrels. When barrels are used, the souring microflora imbed themselves in the wood of the cask and that cask becomes an ongoing vessel for the production of sour beers, adding flavor and complexity. Sour barrels are highly prized by brewers.

Following extended fermentation, the sour beers are often blended with other sour or non-sour beers. Blending is important because the souring process is often inconsistent - with significant variations from barrel to barrel. Blending allows the brewer to produce a consistent product year after year. Once blended, the beers are often bottled and given additional aging. 

Types of Sour Beers

Belgian sours are undoubtably the most classic styles of high-acid beers, with several major style categories. Lambic beers from the Senne Valley are intensely sour and very funky beers made from a combination of unmalted wheat and barley malt. They typically get up to three years of aging before they are released and are often blended. Some lambics are also mascerated with various fruits - notably tart cherries and raspberries - a practice that pre-dates hops as the primary flavoring agent for the beers.  

West and East Flanders ales are other styles of Belgian sour beers. Flanders Red ales from West Flanders are deep red beers with distinct stone fruit flavors, lactic souring and a touch of vinegar on the palate. Flanders Brown ales from East Flanders are darker, more brown, and maltier.

A number of other types of Belgian ales, including the Trappist beer Orval, employ wild yeasts and bacteria to impart a lighter citrusy tartness to the aroma and flavor profiles.

German Sours include Berliner Weisse - a low-alcohol wheat beer with a tart and effervescent profile. Berliner Weisse was dubbed the "Champagne of the North" by Napoleon's troops because it reminded them of Champagne. Another German sour - Gose - has a light tartness and a bit of salt, which enhances it.

American sours are the new kids on the block, but are fueling the current public interest in sour beers in the U.S. While some American sours are modeled after their European counterparts, the creativity inherent in the American beer renaissance is driving the creation of whole new styles of sour beers utilizing innovative ingredients and specialized brewing techniques.

We will explore all these styles of sour beers in detail in future blog posts.

Sour Beers are Here to Stay

Not too many years ago, the tradition of sour beers in Belgium and elsewhere was in danger of dying out. The beers took a long time to make, were labor intensive and sold for the same price as more ordinary beers. The American beer renaissance changed all that by driving U.S. demand for imported sours while creating a strong market for American versions of sour ales. This new generation of sour beer lovers will no doubt sustain the sour market for many years to come.