What makes a sour beer taste sour?

9/27/2017
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Simply put, to make any beer sour, brewers must inoculate it (fermenting the beer by introducing one, or a combination, of fermenting agents - a genus of yeast called Brettanomyces, acid producing bacteria, or any type of non-conventional yeast). When making non-sour beers, brewers ferment the wort (brewed, but unfermented beer) with any number of different species of Saccharomyces yeast. This type of yeast consumes the sugars in the wort and produces alcohol, carbon dioxide, and a range of flavor characteristics. These are controlled fermentations so the beer has a consistent taste.

When it comes to brewing sour beer however, the acid producing bacteria and wild yeast like Brettanomyces are often incorporated in combination with a traditional Saccharomyces species. In the presence of oxygen, Brettanomyces can metabolize alcohol into the vinegary acidity known as acetic acid. In addition to the acidity, Brettanomyces lends a complex array of flavor components - anywhere from earthy and funky to tropical and fruity. These flavors continue to develop and change throughout the fermentation process and can yield some of the most complex beers in existence.

With the popularity sour beer has recently achieved, its incredible to think that sour beer is the oldest beer type in history. Believe it or not, at one point virtually all beers were somewhat sour prior to pasteurization and sterilization practices being completely understood.

Today sour beers have become increasingly popular amongst beer lovers and those that aren’t typically beer drinkers. Beer geeks enjoy the layers of flavors in a sour while non-beer-drinkers love how it doesn’t exactly taste like beer. To put into perspective the popularity gain, from 201502016 the sales of sour beers increased from 45,000 cases to 245,000 cases. Though you can clearly see the popularity skyrocketed just as the accessibility of them has, many people still remain unfamiliar with sour beers, and we’re here to help clarify any and all questions.

When comparing sour ales and more familiar beer styles, the two use different ingredients and fermentation methods. Sour beers have a tart flavor, and are produced using wild bacteria and yeasts, while more well-known beers are made in sterile settings using certain non-wild yeast strains. By using the word sterile, that doesn’t mean that your sour beer comes from a dirty area that will make you sick, but rather means that they are made and formed naturally. Belgium is renowned for creating some of the top sour beers. In Belgium, the sours are frequently aged in oak barrels, which allows the creation to breathe, and the microorganisms to form communities. If not aged in barrels, they can form during the cooling of the wort in a coolship exposing the beer to open air.

Let’s define the parts of a sour beer a little bit before moving any further. Nowadays, the main sour beer influencers are two different bacteria varieties and one wild yeast strain. The two bacteria are Lactobacillus, which turns sugar into lactic acid (the same thing that makes yogurt slightly sour), and Pediococcus, which is often used to add acidity to Belgian beers. Pediococcus can metabolize without oxygen and the acidity will increase the longer its in a beer and over time it can create diacetyl, which imparts a buttery taste to the sour beer.

The wild yeast used is Brettanomyces. Yeast is known for adding the funky earthy quality to beers, but interestingly Brett has a reputation for ruining beer. At its worst Brett can add a repulsive, bitter taste and aroma, but at its best can add a balancing layer of earthiness. Together, the wild organisms are what make this intriguing sour beer so desirable.

So what beers are sour exactly? The list is ever-growing, but the most familiar and crucial to know are Lambic, Flanders, American Wild Ale, Gose, and Berliner Weisse. Lambic beer is technically a Belgian wheat that is spontaneously fermented. It is light and tart, often mixed with cherry and raspberry, traditionally brewed in winter, and aged for at least a year. The blend of both young and old Lambic beers is known as a Geuze.

Flanders is another Belgian beer style, often fermented in large wooden vats, and displaying a palate that mixes and balances acidity with flavors of sweet fruit and vanilla. They come in two forms: Red Flanders and Brown Flanders. Red Flanders generally feature light and fruity flavors, whereas Brown Flanders carry traces of dried fruits such as raisins and plums, balanced by a subtle earthiness.

An American Wild Ale is made by mixing ale yeast and Brettanomyces yeast. Sour flavor and the use of wild yeast, is virtually all that defines the American Wild Ale style.

Gose is a German sour ale made using coriander and sea salt. This style is defined by its incredible balance between flavors of salt, herbs, and of course its sourness. Many are being made in the United States, and of course many are still produced in Germany. Though it’s classified as a sour beer, this beer imparts more of a salty taste than a sour taste, showing how broad the term sour can be when referring to the beer style.

Berliner Weisse is another German wheat beer, this one having a low ABV and high carbonation level. The Berliner Weisse is subtler than most of the Belgian and American sours, since these flavors often come mostly from Lactobacillus, and Berliner Weisse carry a certain tart lemon flavor.

Although the style is deemed a beer, the preparation methods are highly comparable to wine making. Since both are blended, can be barrel aged in oak barrels, and balance sweetness with acidity, the two don’t seem to be two different on paper. On top of this both pair incredibly with cheeses, meats, and fruit, making Charcuterie a great option for sour beers too! We can guarantee however that both have their own unique flavors that make them distinctly a wine or a sour beer.

With so many great new sour beer options out there, we highly recommend you give them a try!

Our beer of the month club recently featured sour beer, Rollingstoner Elderflower Sour from Olvalde Farm & Brewing is a great example of this complicated and intricate brewing process. Cheers!