What makes a beer a sour?

When brewers get to talking about the processes of making sour beers and start saying things like, "I'm going to be introducing bacteria into a turbid mash," there is just something kind of unappetizing about the terminology. Even without getting into the nitty-gritty the idea of a sour beer might just be enough for people to turn their nose up at the style. I think it's unfortunate that the style of beer requires people to get over some preconceptions of the word sour, after all, when most Americans think of sour, their first thought is probably a lemon or soured milk.

Now what most elementary schools don't tell you when you're learning about the sense of taste is that sour doesn't just mean that it puckers your tongue, sour taste is actually the detection of acidity. Even sweet fruits have some measure of sour taste to them: oranges, grapes, some melons, and every citrus fruit. These fruits all contain citric acid, a natural preservative and a source of sour flavor. In beer, sour means the same thing: beers with high acid contents.

New Belgium Brewing Company's sour barrel aging area

Though sour is basically an umbrella term, and any beer can be soured, there are a few traditional styles of sour and about 8 or so "bugs" responsible for souring. Normally considered a flaw, a controlled introduction of sour flavor into an appropriate style can yield a delicious beer once it's had time to mature. Instead of thinking of milk gone bad or biting into a lemon before drinking a sour beer, you should think of a glass of lemonade or a rich wine tart taste. This should help you get the right mindset and realize what to expect when you take that first sip of soured beer.

Classic Styles:

Lambic: Lambics are produced in breweries near Brussels where the wort, produced from a simple grist bill and aged hops, is left in a coolship (a short wide open air tub) that allows for the natural yeasts and bacteria in the air to get a foothold in the beer. Though this is traditional method of preparing a lambic, it has been discovered that the barrels traditionally used for lambics contain more bugs then any amount of air exposure would introduce. Straight lambic is usually difficult to come by, it is extremely sour with very little carbonation and rarely sold outside belgium.
Much more common then the straight lambic is the Framboise, a lambic aged on raspberries, or the Kriek, lambic aged on cherries. Lambics are aged on a variety of fruits. There is also the Gueuze, which is a blend of one to three year old lambics creating a dry cidery or champaigny taste.

Technically Lambics can only be produced in this area, but lambic styled beers tend to be growing in popularity and are produced all around the world by brewers and homebrewers.

Flanders: Another major style traditional sour is the Flanders Red Ale and Oud Bruin.
Flanders Red Ale is commonly considered one of the most wine-like beers produced. It is an interesting brew with a porter-like grist, though use of Vienna malts dominate the bill and impart the red to burgundy color. A flanders red is innoculated with souring bugs in an open air method like the lambic. A Flanders Red Ale usually ends up with a plum, cherry, or currant taste.

An Oud Bruin, or Flanders Old Brown is a beer of rich history. For a long period this beer was probably synonymous with the term beer, as whatever caused fermenation was still unknown and uncontrolled, not to mention the use of pale malts was limited to the local of their origin. The Oud Bruin grist is mostly pilsner and munich malts with some adjuncts. The beer generally ages for a year or longer in order to mature the sour flavors and allow them to mellow. The beer has a bright aroma and a sweet fruity taste, though there is certainly a sour acidic element to the style.

These are the two traditional Belgian sour styles that have survived through the ages. It's important to note that any style can be soured, and often can come out tasting quite well. This is one of the reasons I've been so into Jolly Pumpkin, since they have Ambers, Goldens, and several other styles that they have soured.

This entry is getting kind of long, so I'll post about the souring "bugs" in an entry tomorrow.