A professional brewer friend once told me that, for him, the American sour-beer renaissance has been like being confined to a brewhouse his entire life, knowing no different, and then throwing open a window to glimpse a bright, wild, vibrant world filled with possibility and ripe for exploration. And yet many beer drinkers, having tried a sour or three, tend to limit their expectations to a very narrow view.
In reality, sours are a broad-reaching category that encompasses a breadth of styles and brewing techniques—from historic lambics and other traditional Belgian and German brews to today’s Wild West of experimental sours and wild ales—as well as a wide range of flavors and intensity.
The Science of Sour
Many sour beers are fermented, in full or in part, using a strain of Brettanomyces. Brettanomyces, or Brett for short, is a wild cousin of domesticated brewer’s yeast that was first discovered growing on fruit skins. Winemakers consider it a spoiling agent and go to great lengths to keep it from contaminating their cellars, but sour-beer brewers have embraced it. It’s especially good at chopping up long chains of sugars that Saccharomyces won’t eat and converting those sugars into alcohol and CO2. Brett also imparts a wide range of esters and phenols—often described as earthy, fruity, musty, or funky depending on the specific strain used. These rustic, wild flavors go a long way toward giving sour beers their character, but _Brett _isn’t what makes a beer sour.
What our palates perceive as “sour” is really a taste response to the acidity level in a beer—namely acids that microbial bacteria such as Pediococcus _and _Lactobacillus create. Once inoculated into the beer, the bacteria feed on what’s left over after fermentation and, over time, create lactic acid. They can also create acetic acid (vinegar), which can be desirable at low levels but is generally considered an off flavor.
Brewers manipulate this process by:
- varying the ingredients in the base beer
- varying fermentation temperatures and times
- varying whether Brett is introduced during primary or secondary fermentation and which strain is used
- varying how and when bacteria is introduced
- adding adjuncts such as fruit or other ingredients
- barrel aging and blending together batches
It all multiplies into countless permutations. But, for all the variables that brewers can control, there’s also the unpredictable element of nature at work that’s so appealing to brewers and beer drinkers alike.
Here’s an overview of some of the better-known styles in the sour spectrum and how they develop their individual characters and flavors.
Lambic Beers
All lambics are spontaneously fermented by naturally occurring wild yeast. It’s how beer was first discovered and a method that predates human knowledge of yeast, bacteria, and other forms of microscopic life. Only a handful of breweries in the Senne Valley near Brussels, Belgium, produce true lambics. These are the breweries, such as Cantillon and Boon, that famously preserve the dust and cobwebs in their brewhouses and barrel rooms, lest they disturb the colonies of microbes that give the beer its distinct character and local flavor.
The grist bill for lambics includes a high proportion of unmalted wheat in addition to malted barley. Aged, oxidized hops are used for their antibacterial properties rather than to impart bitterness, flavor, or aroma. A turbid mash—in which a cloudy liquid portion of the mash is drawn off, heated, and then reintroduced to the mix—is also traditional and results in lots of unconverted starches and dextrins that help sustain the bacteria after the yeast has finished fermentation.
The sweet wort is poured into a large, shallow container called a coolship (koelschip), where it cools overnight in the open air and collects ambient yeast cells, bacteria, and other tiny critters. The beer is then transferred to large oak barrels to ferment, where more buggy residents go to work. Fermentation often takes a year or more to complete and to develop the desired acidity.
Finished lambics are also used as base beers to create several related styles. Older and younger lambics are blended together to make gueze, for example. The blended beer undergoes a secondary fermentation in the bottle and finishes with a champagne-like effervescence with a mild oak aroma, fruity esters, and balanced acidity. Faro is a sweetened variant made by blending in dark candi sugar and caramel.
Fruit lambics are made by adding whole fruit, fruit pulp, or fruit juice to a batch of lambic as it ages in oak casks. The fruit helps balance the beer’s tart acidity, and the added fruit sugars initiate a secondary fermentation. The beer might be blended again with a younger lambic before it’s bottle conditioned. Kriek, made with cherries, and framboise, made with raspberries, are the most common fruit lambics; however, just about any kind of fruit can be used. For example, Brasserie Cantillon’s Fou’ Foune is known for its use of apricots, and Guezerie Tilquin’s Quetsche is named for the plums added to the lambic.
Flanders Red Ale
Rodenbach Brewery, founded in 1821 in the West Flanders province of Belgium, is practically synonymous with Flemish Red-style ales. Specialty malts give the base beer its distinctive red hue, and a long maturation period in oak barrels inoculated with _Lactobacillus _and other bacteria gives the beer its acidity. Older batches are blended with younger beer to help balance the flavor and acidity before bottle conditioning. While no fruit is added, fruity esters and phenols reminiscent of black cherries, raisins, and stone fruit are common and give the beer a vinous character akin to full-bodied red wine.
Oud Bruin
Oud bruin is a similar yet distinct Belgian-style sour traditionally produced in East Flanders. Brown ale is used as a base beer; it is then aged in oak casks for as long as two years (hence an “old” brown) to ferment, mature, and develop lactic acidity. Again, older batches are blended with younger beer and bottle conditioned. The interplay of fruity esters and rich malts characterizes the style, with low to moderate acidity and some barrel character.
Gose
Not to be confused with gueze, gose is a traditional German-style unfiltered sour wheat beer that’s currently enjoying renewed interest among American craft brewers. Westbrook Brewing Co. in South Carolina, DESTIHL Brewery in Illinois, Anderson Valley Brewing Co. in California, and others have all released riffs on the style.
The gose grain bill consists of at least half malted wheat in addition to malted barley, with coriander and salt added during the brewing process. Traditional gose is spontaneously fermented; however, top-fermenting ale yeast can be pitched for primary fermentation. The result is a low alcohol, lightly tart, and lemony wheat-based beer characterized by its clean lactic acidity and notes of salt and earthy spice.
It’s more common today to see U.S. brewers using the kettle-sour method to achieve the sour aspect of gose, rather than longer mixed-culture fermentations. Using this method, brewers follow a traditional mash and lauter regimen, transfer wort to the boil kettle, then pitch Lactobacillus into the wort and let it sit (the time in the kettle varies depending on the level of intended sour, from a few hours to a few days). They then boil to kill off the _Lactobacillus, _and ferment with brewers yeast.
This process is much less expensive and less time-consuming than traditional mixed-culture fermentation, and as a result certain commercial brewers have begun to use the process for other styles of sour beer.
As a general rule, less-expensive sour beers are typically kettle soured, while beers that spend a year or more in barrels or tanks souring with mixed-culture fermentations command higher price points. But there are definite exceptions to this, and the process used does not necessarily correlate to “better” or “worse” taste in the glass—that’s entirely up to the skill of the brewer.
Berliner Weisse
Berliner Weisse is another variety of sour wheat beer. The style originated in Germany near Berlin and was hugely popular there during the late 1800s. It has also enjoyed renewed interest from American craft brewers.
The grain bill is typically evenly split between malted wheat and malted barley, although some modern brewers dial the wheat way back. Lactic acid is primarily created through added Lactobacillus, either in a cask or through bottle conditioning. The finished beer is very low in alcohol—around 3 or 4 percent ABV—with a mildly tart, clean, and fruity character and a dry finish. Berliner Weisse is traditionally accompanied by fruit syrup, such as green woodruff or a berry syrup, that’s added at serving for a shot of sweetness and additional complexity.
Most commercial examples of Berliner weisse available in the United States are now brewed using the kettle-sour technique, similar to gose.
American-Style Sour Ales
Style guidelines for American-style sours are intentionally nebulous because American brewers are still rewriting the rules. Many are inspired by traditional sour styles, which are used as a jumping off point to experiment with techniques such as hops additions for bittering and aroma, racking sour beers into freshly used wine or spirit barrels, blending together batches, adding adjuncts, or just about anything else they can think of.
Balanced acidity and an overall harmonious complexity are desirable in most examples of sours, as is the absence of jarring off flavors or obvious flaws. Otherwise, the possibilities are wide open.