Want to see a grown brewmaster shake in his boots? Just bring a vial of Brettanomyces into his brewery and toss it up into the air a few times. Brettanomyces is a strain of yeast that, given the opportunity, will absolutely take over a brewery and infect every surface, fermentation tank, and bottle in the place. In most beers, the organism can produce undesirable sour or acidic off-flavors. But, to a brave few brewers, those off-flavors are a source of complex and often delicious artistry.In Belgium, sour beers are nothing new. For centuries brewers have been crafting brews that are sour, acidic and utterly delightful. One such style that has been gaining ground in the United States is Flanders Red, an aged ale that obtains its sour characteristics from Brettanomyces or lactic acid. An excellent example of this style is Rodenbach.

Another Belgian sour style is Lambic, a spontaneously fermented brew that is aged for a minimum of three years before leaving the brewery. Because the yeast that inoculates this brew is only found in Belgium in and around Brussels, the style cannot be made anywhere else. The brew that results from the combination of wild yeast inoculation, aging, and blending is powerfully sour and yet refreshingly bracing. The brew is often fermented with various fruits to produce sweet and sour combinations such as kreik (cherry), framboise (raspberry), and peche (peach).

But, back to Brettanomyces. Brett, as it is called by many in-the-know beer aficionados, competes with brewer’s yeast, and other microorganisms, in fermenting the wort, giving the beer a distinctive sour taste. The yeast is notoriously difficult to clean and can easily get out of control and colonize a brewery spoiling other beers that are not supposed to taste sour. In fact, the yeast strain is considered a spoilage organism in the wine-making industry that can impart “sweaty saddle leather”, “barnyard”, “burnt plastic” or “band-aid” aromas to wine. But, in beer, the yeast can create aromas one might consider musty, and flavors that are often described as funky.

Brett turns beer sour by eating the sugars that are left in beer by normal brewer’s yeasts. The result is a sour-tasting brew that is something of an acquired taste. Other organisms that bring on the funk in beer include lactobacillus (also found in fermenting yoghurt too) and pediococcus, which provide sour, tart notes and acetobacter, which gives a beer vinegary component.

The best way to decide if you like these unusual, yet rewarding brews is to seek one out and just give it a try. You may be surprised at how much you enjoy the labors of the little beasties that some might call an infection while others might call a blessing. Just be careful if you do decide to toss around a vial of Brett, you certainly would not want to cause your local brewmaster to ban you from his brewery.

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