A Disquisition on the Nature of Sour

I'm not totally sure why tastes are broken down into just five categories (salty, sweet, sour, bitter, and umami), but what's interesting is that two of the three most characteristic beer flavors--sour and bitter--are considered "aversive." That is, they are signals our ancient adaptive brains recognize as containing potentially lethal substances. These categories of taste are subjective and culturally specific. So much of the terrain of flavor exists well outside their small purview--but somehow they persist.

One of these flavors is the subject of today's post: sour. What is sour, and when should it apply to flavors found in beer, and particularly, should we consider brettanomyces-inoculated beer sour? The answer is semantic, not scientific, but that's fine: it's best to have a shared vocabulary in discussing the flavors present in beer. Back when I reviewed this year's Dissident, I classed it as a sour beer, and Ezra took issue with this. A few weeks ago, the Brewers Association signaled they were in accord with Ezra's view and split brett-inoculated beer off from the category of "sour." And then last week, when I was chatting with John Harris, he also made the point. So, what's sour?

The Nature of Sour
What we call "sour" is the perception of acids. Vinegar, is a great example; it takes most of its sour quality from acetic acid, but also has small amounts of citric acid and tartaric acid. In beer, lactic acid is a big player in the perception of sourness. Impressionistically, it's that puckery quality. Linguistically, there's no precise distinction between "tart" and "sour," though beer people will typically ascribe to more lightly-soured beer the adjective "tart." I'm cool with that.

The Nature of Wild
Wild ales almost always produce sour flavors, but they usually produce lots of other flavors, too. Many of these are referred to by similarly wild-sounding adjectives: horse-blanket, zoo-like, goaty, sweaty. Other qualities seem to come from chemistry labs: nail-polish remover, paint thinner, etc. Still others are less precise--dusty, austere, hot, sharp, funky, tangy. The process of fermentation produces lots of chemical by-products, and no doubt a sophisticated lab could identify all the compounds that produce these varying flavors. Some are related to sourness, some are miles away. I have been lax about using the words "sour" and "wild" interchangeably, and this definitely confuses matters. If a beer is zoo-like, it's best not to refer to it as sour.

Is Brettanomyces Sour?
So then we come back to our friend, brett. Many of the qualities it produces aren't traditionally sour. But it can produce sour notes. At halftime of the Super Bowl, we cracked a Billy the Mountain--a beer soured with brettanomyces clausenii. (The Packers were ahead and I wanted to celebrate while we had the chance--no waiting until the end of the game for this pessimist!) And yes, it is sour--or at the very least notably tart. In fact, the signature quality the brett contributes to the Billy the Mountain is tartness/sourness (though there are other, more subtle harmonics, that figure in). This isn't always the case--this year's Dissident, for example, has many wild qualities, but its acid is less sour than dry and leathery. One of the by-products of brettanomyces is acetic acid, though it doesn't always crank it out in huge quantities. Beers made with brett can therefore be sour or not. They are the chimera of the sour world.

The upshot to all of this is that I feel suitably chastened about my cavalier substitution of the word "sour" for "wild." As a matter of coming to shared vocabulary, using the word sour should be restricted to flavors that are, in fact, sour. On the other hand, it is not strictly true that brett beers are not sour, either. (Claiming they're just "tart" is a scoundrel's refuge.) This is especially true when we're trying to come to shared vocabulary. Compared to standard beers, something like Billy the Mountain has to be considered sour. It's an abstraction to exempt it because the sourness is lighter, different, and more subtle than in other soured ales--and to the average beer drinker, a bizarre elision.

In conclusion, to the question "are brett-inoculated beers sour?" we must agree to the answer "yes." And "no." Thank your for your attention.