So I thought I'd write a bit about one of my favorite "styles" of beer, if it can really be called that, as well as what is certainly one of the most interesting beer styles out there.
There's a lot of confusion as to exactly what a sour beer, or wild ale, is, so I figured I'd run through the way I like to think of sours. In my mind, three things contribute to the making of, or identification of, a sour beer, also called a wild ale: flavor, technique, and the organisms used to make the beer.
Flavor
Sour beers, believe it or not, come in a variety of flavors. I like to think of two main "types" of flavor you can expect to find. On one end of the spectrum, you incredibly acidic and tart notes. This can come in the form of a tart, citric flavor, a tartness similar to a tart apple or berry, or even a vinegar-like acidity. On the other end you have funk. These are the flavors and aromas that wine geeks would call "barnyard, haystack, horse blanket," etc. Both are important parts of sour beers, and can be present on their own, or combined with each other.
On the extreme tart end, you'll find traditional berlinerweiss, as well as many fruit beers. The tartness can come from the fermentation and brewing process, or from the addition of fruit, which can be added specifically to add tartness, or to feed the microorganisms which create tart flavors in sour beers.
On the other end, you have funky wild ales. Think the funky, earthy, flavors of a saison, but on steroids.
Most sours fall somewhere in between the two extremes, with perhaps the best example of both types of wild flavors complementing each other being the Flanders sours, both red and brown.
Technique
Traditionally, sour, or wild ales, were created using spontaneous fermentation. That means a wort was created, and then left to be fermented by the yeast and bacteria that was in its natural environment. While these included some yeasts related to our modern brewing yeasts, which eat sugar and create alcohol and carbon dioxide, they also included all kinds of other things which added their own, unique flavors.
This spontaneous fermentation could come in the primary fermentation (when you're actually making beer out of malt), or could come in the form of a secondary fermentation, where a beer is aged either in an un-sterile oak barrel, or out in the open, allowing wild yeasts and bacteria to eat up any residual sugars. Often, fruit is added after the initial fermentation both to flavor the beer, and to provide more food for these wild yeasts.
The Microorganisms at work
The most important factor is the actual yeast and bacteria involved, especially in modern brewing. In fact, most brewers no longer use truly spontaneous fermentation. Instead, we generally add the same types of yeast which traditionally were responsible for spontaneous fermentation on purpose. One of the things that makes sour beers so interesting is that the three main types of yeast used for this purpose,
brettanomyces, lactobacillus, and pediococcus, are traditionally though of as causing flaws in both brewing and wine making. In fact, they are three of the main yeasts that traditional brewers and winemakers struggle to keep
out of their tanks.
This explains in large part why these beers aren't really spontaneously fermented any more. First of all, in order to get those yeast strains into a beer, and keep other more harmful beers out, you'd have to find the perfect environment. Second, that environment would pose a huge risk to any non-sour beers you had brewing in the same brewery.
So, instead, these three, and perhaps other, "wild" yeast strains are added by the brewer to the beer (before, during, or after primary fermentation), in order to make sure they wind up where they are supposed to be. These yeasts, however, unlike most modern brewer yeasts, are still unpredictable. They can die unexpectedly, or can go truly wild, turning a good beer into vinegar. Sour beer production requires constant monitoring by brewers and technicians, both to make sure the souring microorganisms are well fed and healthy, and to make sure that the end result is both safe and enjoyable.
Essentially, much like blue cheeses, sour beers may seem scary to some. What is really happening is that a brewer is deliberately spoiling their product in order to achieve a unique and interesting product. Then again, all alcohol and cheese production is essentially the deliberate spoilage of the base ingredients. Blue cheese and sour beers just take it to the extreme, both in process and in flavor.
