A Beginner's Guide To Sour Beer

Sour beer is not your usual beverage. The adjectives and metaphors used to describe it aren't exactly typical either, with "barnyard," "wet hay," and "funk" all being popular descriptors. While these serve to highlight sour beer's distinctness, this representation does little to reveal the refreshing, addictive, and lip-puckering experience of sipping on one. These descriptors also fail to expound upon the wild, time-intensive nature used to make what is the oldest type of beer in the world, per National Geographic.

The beer's arduous production process, complex and startling taste, and higher price point have seen this variety rank amongst the least accessible forms of the beverage. This nearly caused the style to disappear from the international beer market altogether, as reported by Caña. Sour beer's survival was anything but guaranteed during this time, especially as consumers began favoring hop-forward craft beer and sugary hard sodas.

Sour beer has erupted in popularity in recent years, with sales rising by more than 40% in both 2018 and 2019, per Information Resources Inc. (via Forbes). Here's what's behind this dramatic uptick in interest and why you should try beer's latest (and perhaps most unique) craze. 

Mead is widely believed to be the oldest alcoholic drink made and consumed by humans, with archaeological evidence highlighting that it was consumed approximately 9,000 years ago, as reported in Proceedings of the National Academy of Sciences of the United States of America. In comparison, the first evidence of beer — defined as an alcoholic drink made with yeast-fermented malt — being brewed comes from what is now modern-day Iran some 5,500 years ago.

As highlighted by The New Yorker, a minimal ability to manipulate temperature, haphazard cleaning techniques, and a lack of control over the fermentation processes meant all beer before the 1800s was somewhat sour. The tart flavor developed as a result of the wort — the sugary liquid that turns into beer when fermented — being exposed to air when cooling. Wild yeast strains and bacteria in the air entered the beer during this time and began the fermentation process. Each strain of yeast and bacteria imparted a different flavor, resulting in a beer with numerous tasting notes.

All of this changed when temperature, cleanliness, and yeast strains began to be controlled in the mid-19th century, thanks to the pioneering work of scientist Louis Pasteur. Practices, such as using a single, specific yeast strain, enabled the production of beers that were consistent and predictable. However, these beverages also lost the complexity that came from the layers of flavors imparted by numerous wild yeast strains.

The process of wild yeast and bacteria inoculating beer is called spontaneous fermentation. This means of fermenting has been sidelined since the advent of Louis Pasteur's work; however, it has been making a comeback in recent years, appearing in beer, wine, and liquor, per Bon Appétit. This is largely due to the fact that a wild, diverse combination of yeasts and bacteria will typically produce an end-product with a strong and wide-ranging flavor profile.

Spontaneous fermentation is achieved during the production of sour beers by leaving recently boiled wort to cool overnight in a large container, called a koelschip. This is the traditional means of producing iconic types of sour beers, such as lambic beers, and is the step directly responsible for the end-product's multifaceted and exciting flavor, as highlighted by VinePair.

Unfortunately, spontaneous fermentation poses some serious commercial challenges. Chief among these is that these beers cannot be brewed all year round. As a study from the Institute of Brewing & Distilling notes, beers made via spontaneous fermentation can only be brewed during the cooler months, as warmer temperatures increase the chances of spoilage bacteria entering the beer. Of course, an inconsistent supply of beer is a huge issue for those looking to establish themselves in the marketplace. As such, many sour beer producers use a standard fermentation process which can be performed all year round, before adding wild yeast and bacteria at a later point (per Brewing Science).

According to the New York Times, sour beer is the umbrella term for a range of beer styles that present an acidic, tart flavor profile. The oldest and most well-known type of sour beer is lambic beer, a Belgian beer that is made via spontaneous fermentation. Lambic also forms the basis of another noted Belgian beer called geuze, a blended beer that we will learn more about later.

One of the key factors that define lambic is the aging process it undergoes. Traditionally, it is aged in large, oak barrels and takes one to three years. Numerous microorganisms are present within the wood of these barrels. Over time, they will enter into the beer and cause it to ferment further, which, in turn, impart more flavor.

Another type of sour beer is gose, a salty and refreshing beverage that is light and delicate. Lepzig brewer Henryk Szymczak described the flavor profile in an interview with Eater. "It's not so strong as compared to the Berliner Weisse or any of these specialty Belgian beers," he said. "It's a relatively medium sourness, and it has a little bit of a fruity flavor."  

This saline yet highly drinkable beer seems tailor-made for hot summer days. Gose has even gained acclaim from publications including The New York Times. This has led craft brewing giants, such as Sierra Nevada, to create their gose-inspired beer, per the Los Angeles Times.

Nearly all non-craft beers produced in modern-day breweries use one type of yeast strain, per Frontiers in Genetics. As it is integral to the product, a brewer's yeast strain is often kept secret, and in extreme cases even put under armed guard. While these strains are unique, most of them belong to the Saccharomyces family. This yeast has an affinity for sugar and rapidly consumes it, producing alcohol and carbon dioxide as by-products, per Beverages.

Sour beer differs from its counterparts in that it is made using two strains of yeast: one from the Saccharomyces family and another from the Brettanomyces family. The latter is a common, airborne yeast that enters the beer during spontaneous fermentation. Instead of absorbing sugar, Brettanomyces converts alcohol into acetic acid, the compound that gives sour beers their lip-puckering taste, per BrewDog. 

Brettanomyces is also the yeast responsible for sour beers being described as funky or barnyard-like, according to Punch. This is because concentrations of the yeast produce an odor that many associate with a barnyard setting, with scents of damp horse, wet hay, and leather often standing out. 

By its very nature, the process of spontaneous fermentation opens the beer up to being altered in ways that the brewer cannot entirely control. From a creative perspective, this process may seem expressive and engaging. However, from the commercial side, it makes marketing and selling products more difficult. This is because one wildly different or subpar batch can put consumers off the product for life, according to Brewer Magazine.

Despite the variables introduced by spontaneous fermentation, there are several ways brewers can ensure their sour beer remains consistent across different batches. As reported by Thrillist, controlling temperature and cooling times will go some way in maintaining consistency. However, discrepancies between multiple batches may still arise. To establish better consistency, brewers turn to blending, which involves mixing different batches of the same beer together to create a uniform product. Whiskey and other liquors have long undergone this process for the very same reason (per Serious Eats).

In a method that evokes images of wine or whiskey, sour beer is frequently aged in wooden barrels for prolonged periods. As previously stated, this aging adds complexity and nuance to the beer. However, the ways that sour beers are affected by barrel aging vary greatly depending on the beer's original properties. As reported in the International Journal of Food Microbiology, bitter beer inhibits the development of bacteria. This, in turn, limits the impact of this second fermentation period and the effect barrel aging has on the beer.

The same study also demonstrated that beer with a higher alcohol content will draw out a great deal more of the wood's compounds than weaker beer. As highlighted by VinePair, the increased prevalence of these compounds darkens liquids while also adding a range of complex aromas, flavors, and characteristics.

Despite this process being markedly more time-consuming than the production of standard beers — some sour beers can be barrel-aged for up to three years — there is a growing market for barrel-aged beer of all types. Such is the excitement around barrel-aged beers — and the premium price they can demand — that some brewers have been caught claiming barrel-aged status when their beers are nothing of the sort, as reported by The Drinks Business.

Spontaneously fermented sour beers are somewhat unpredictable. Blending is one key process that ensures sour beers remain uniform from batch to batch. However, the art of beer blending is not solely used to ensure consistency; it can also be used to create new and exciting products from a variety of beers. As such, blenders form a key part of the sour beer industry.

Indeed, entire sour beer styles have been built from the blending process. Gueuze, a unique type of lambic, is one such example. Made from mixing one-year-old lambic with varying proportions of two- and three-year-old lambic, gueuze offers a unique flavor profile. The flavors further develop during a second fermentation that occurs in the bottle. The resulting density of flavor and high carbonation has led drinks writer Anthony Gladman to opine that gueuze is even "a great replacement for champagne," clearly demonstrating the power wielded by sour beer blenders.

Blenders are also responsible for modern-day innovation in the sour beer industry. As Greg Engert, beer director of Neighborhood Restaurant Group, explained to The Splendid Table, many blenders popularize unique processes, such as fermenting the beer with fruit to add twists to their finished products.

The complexity, nuance, and cost of sour beers has not stopped them from becoming a popular option among many beer drinkers. As noted by Time, sour beer began to really take off in the United States around 2016 when 245,000 cases were sold. These sales have continued to grow, often by more than 40% each year, per Information Resources Inc. (via Forbes). Now, sour beer features in the repertoire of U.S. craft brewers both large and small. The U.K. is experiencing a similar upswing in sour beer popularity, with many recently-launched breweries producing only sour beer. 

Interest in sour beer is thought to have risen predominantly from the beverage's unique flavor, a notion verbalized by Nick Ziegler, a brewer at Magic Rock. "Why is there so much demand? It's all down to complexity," he explains in an interview with the Independent. "With the same three ingredients it takes to make a regular IPA or bitter you can create something really rich, interesting and beautiful — something that challenges what many people think of as beer."

The traditional means of producing lambic and other sour beers is by spontaneous fermentation in a koelschip. The majority of brewers who choose this method leave the liquid to cool overnight, thus allowing the yeast sufficient time to inoculate and begin the fermentation process.

As previously mentioned, beer produced in this method should only take place during the cooler months to reduce the risk of bacteria ruining it. In Belgium, the home of lambic, the brewing season runs from October to April. Beer produced outside of these times is dismissively labeled as bezomerd, or beer that has been exposed to too much heat.

However, as reported by The Guardian, the warmer seasons caused by climate change have already begun to seriously diminish the brewing season. At the famed Belgian Cantillon Brewery, The brewing season has become about 25 days shorter than in the early 1900s. To compound this issue, erratic temperatures can also lead to beer being dumped, as rogue night-time temperatures can cause whole batches to spoil.

Despite sour beer becoming increasingly popular in global markets, the beer's ancestral home is undoubtedly Belgium. The country has a long, beer-making culture, one that has always championed a range of styles. Originally, this took the form of beer flavored with a mixture of herbs — known as gruit — before hop-based brews became popular in the 18th century.

Critically, Belgium, unlike Germany, didn't pass any purity laws that limited the inclusion of ingredients in beer. This meant that gruit-style beers and other alternatives, such as wheat-based lambic, were not abandoned by brewers. As a result, Belgium retained its highly diverse beer culture, while Germany's became steadily homogenized.

Such is the influence of Belgium on the sour beer scene that many contemporary non-Belgium producers sought to copy the country's techniques. Most of these non-Belgian beers were originally marketed as lambics or geuzes. This caused tension among traditional brewers who argued that lambics (and by extension, geuzes) could only be made in the traditional areas of Belgium. As a compromise, brewers outside of the traditional regions came up with the term Méthode Traditionnelle. The term indicates that they follow traditional brewing procedures without detracting from authentic Belgian beers.

The powerful and arresting flavor profile inherent to most sour beers would lead people to assume that they should be enjoyed by themselves. However, with a bit of planning, nearly all sour beers can complement a range of foods by boosting their flavors and benefiting the meal.

Serious Eats notes that while the category of sour beer encompasses a wide range of the beverage, the vast majority pair well with a few general flavors. Typically, these include bold and intense notes, with salty and fatty dishes being particularly tasty when served with a glass of sour beer. The one exception to this rule is gose beer, which pairs well with just about everything, according to several reviews on BeerAdvocate. Reviewers note that it pairs well with seafood, smoked meats, and salads, and can even be used to make sauerkraut.

By their very nature, sour beers offer a wider range of flavors than traditional, single yeast strain beers. This is not lost on New York Times wine critic (and gose lover) Eric Asimov. He highlights how sour beers, such as gose, provide a rare mixture of flavors that are not traditionally associated with beer, including salt and spice.

Barrel aging will also add further dimensions to the flavor of a sour beer. Greg Engert, beer director for the Neighborhood Restaurant Group in Washington, D.C., highlighted the impressive changes that take place during barrel aging. "All those wild yeasts, ale yeasts, lager yeasts, and bacterias that are in the air are also in the oak barrels because oak has sugar in it," he said to The Splendid Table. "These wild yeasts and bacteria will feed on the oak until a new sugar source presents itself. Once we get this lambic in a barrel, it's going to continue over the next three years to develop sour flavors, funky flavors, and pick up some nice oaky tannins and vanillins as well."

Terroir, a term used to describe how environmental factors can affect an end product, is a word generally associated with wine production. However, there is a growing consensus that beer is just as affected by the environment in which it is produced. As reported in Good Beer Hunting, most modern beers largely gain a sense of terroir through the hops that are used to flavor the beer. However, as sour beer is made without hops, terroir is expressed in another way — most notably through the yeast that inoculates the beer.

Making a beer that represents the brewery's area is something many owners and brewers are extremely passionate about. This is exemplified by Jeffrey Stuffings, co-founder of Jester King Brewery, in an interview with First We Feast. "The challenge of making our own spontaneously fermented beer was really appealing to us," he said. "Also, we're a brewery that thinks it's important to make beer with a sense of place, meaning that our flavors are unique to, and derived from, our location. Using a coolship to catch wild yeast from the Texas Hill Country for fermentation is one of the best ways we can think of to make beer with a sense of place."