I first encountered Duchesse de Bourgogne in a beer flight at Slater's 50/50. Upon first sip of the reddish-brown ale, the other beers in the flight ceased to be relevant. Don't blame the other beers though; the distinct, mouth-puckering sourness of the Duchesse makes it a show-stealer next to anything.
Brewed by Belgian Brouwerij Verhaeghe, Duchesse de Bourgogne is a Flemish red ale, a blend of 8-month-old and 18-month-old ales, in this case. As with all red ales, the drink gets its characteristic sour and tart quality from lactic acid, while aging in oak barrels imparts a deeper body. The drink is named for Duchess Mary of Burgundy, a filthy-rich medieval heiress who suffered an unfortunate (and deadly) fall from her horse–it happens.
Devoid of hoppy bitterness, Duchesse de Bourgogne is almost wine-like. The sourness is a total palate-shocker, and the slight vinegary undertone may make you turn away initially, but stick with it, and you'll discover a pleasant fruitiness recalling sour cherries. The beer resembles a fruit Lambic, though it's less sweeter and more tangier. Even with the mouth pucker, the beer is a smooth and easy drink. You may find yourself with the warm and fuzzies after downing a pint too quickly.
Duchesse can be found in the imported section at Total Wine and More. It's a pretty penny, $15 for 750 ml or $20 for a 4-pack, but it's a worthy special-occasion beer.