What Makes That Beer a Sour?

Sours are among the most intriguing classes one is likely to encounter within the beer. In the last decade, this style’s popularity has fluctuated from being a solitary drink to a reliable stalwart within the craft beer movement. However, it’s technically one of the oldest ales available on the planet. And, even with the fact that it has gained new popularity, sour ale remains elusive to identify fully, even if you inquire about the most abundant drinkers. That’s all I’m saying. If you’re in search of some clarity on this subject, there’s no shortage of people who want to help.

A beer that has a different name is sweeter.

In the simplest sense, “a ‘sour beer’ is any beer where acidity forms the backbone of the beer’s flavor structure,” according to Garrett Oliver, legendary brewmaster at Brooklyn Brewery. “For most beers that role is occupied by hop bitterness, which acts like tannins in red wine. Sour beers have a structure more like white wine, with acid in the center.”

It is the organoleptic method to describe the style determined by the extent to which we detect some sourness in the tongue. This is, in essence, a representation of the number of hydrogen ions floating around in your sour, and the higher the number of floating particles, the more acidic or bitter the beer will taste.

Do you remember the word pH from your high school Chemistry class? It is actually “potential hydrogen,” a logarithmic indicator of the amount of individual ions in it. Water is considered neutral if it has seven pH; however, a liquid with six pH is ten times more acidic, meaning it has the tenth of hydrogen ions. A standard lager or ale is usually between 4-5 pH. A sour is close to three. It’s not a massive amount of a shift; however, be aware that this is ten times more acidic than water!

How does sour acquire its strength?

There are various methods by which beer can be made to suit this particular taste profile. “Sour beers are [most often] made acidic by lactic acid-producing bacterial strains,” says Oliver. “Wild yeasts can also produce some acids, but lactobacilli — the same critters that sour yogurt — are usually the main actors here.”

The microorganisms are added at various stages of brewing for multiple effects. In a process known as “simple sour,” they are introduced within the beer (the grain-steeped liquid, which provides the sugars needed to allow fermentation) over up to two days before when all of it is cooked and then fermented as it would be traditional beer. This creates a light version of tartness, typically perceived by smell rather than taste. When you use “mixed fermentation,” those bacteria mentioned above are introduced together with yeast. This results in and lower the alcohol content of the beer as it absorbs alcohol.

A flaw or a feature? Depends on who you ask

There’s also wild ale, a sour-adjacent type where the yeasts present in the immediate surroundings in the brewhouse are permitted to ferment the wort naturally. This is because the Belgians have been making beer using this method since the 13th century, in a style referred to as lambic. Absent in this style are domesticated types of yeast, which have been grown for generations to keep the beer clean and uniform. This is why the Germans who make their beer, a nation known for its laws regarding the purity of beer–generally disapprove of the style. They’re more likely to see the flaw as a problem rather than an issue.

Many modern brewers fear introducing wild yeast strains like Brettanomyces in the brewhouse due to worry that they could accidentally affect production lines. In their turn, the Belgians devised a method to ensure consistency year after year by combining various lambic vintages into a batched category of wine called “gueuze.” This wine ferments for several years after bottling, resulting in an unofficial name: “The Champagne of Brussels.”

If produced in the US, the beer is more often referred to as American Wild Ale, as is the case with Russian River Brewing Company, an adored company located in Santa Rosa, California, that has helped to popularize the style across the United States. While these beers tend to tend tartness when grouped with other sour beverages can confuse consumers’ perception of the category. “It’s important to understand that Brettanomyces yeast does not make a whole lot of acid,” clarifies Russian River co-founder and brewmaster Vinnie Cilurzo. “Instead it contributes more funky and wild qualities to the beer. It’s also important to distinguish the difference between acidic and acetic. We want a light acid contribution which I call acidic, however, we do not want acetic which is more like balsamic vinegar.”

That is to say that there, aren’t all sours made equally? Some are even sour regardless of what Titratable Acidity (a measure of the acid content in beverages or food) in the bottle appears to read. Like any beer master, Brewmaster will extract desired flavors in the design process, leaving nothing to chance. “At Russian River, we age the beer for long periods in the barrel with brett, lacto, and pedio (lactobacillus and pediococcus, respectively; the most common types of bacteria used to sour beers) and over time these yeast and bacteria work slowly to develop the unique tart and wild notes that all of these microorganisms contribute,” says Cilurzo. “Sometimes these beers will be quite sour but we try for a more subtle contribution. I’d prefer to have more Brett contribution as compared to the sourness from the two bacterias.”

Do your beers contain probiotics?

Some of the sours on the shelves today have a similar flavor profile to kombucha, which is a popular tart beverage. This commonality has led drinkers who are health conscious to ask if sours, as their sour counterparts, could also be classified as “probiotic.” Here, brewmaster Garrett Oliver spills the tea:

“In the ‘simple sour’ — also known as ‘kettle sour’ — technique, the wort is boiled after the souring, and no probiotic bacteria survive. But both mixed fermentation beers and wild-fermented sour beers will usually contain live bacteria unless they’ve been pasteurized after fermentation.”

For those looking for something gluten-free, The news isn’t as sweet. Oliver says that if there’s gluten present in the grains used in the process of making it, the beer will also contain gluten regardless of whether it is bitter or sour.