Flanders red ale, Flemish red or Belgian red ale is a style of sour ale usually brewed in West Flanders, Belgium. Although sharing a common ancestor with English porters of the 17th century, the Flanders red ale has evolved along a different track: the beer is often fermented with organisms other than Saccharomyces cerevisiae, especially Lactobacillus, which produces a sour character attributable to lactic acid. Long periods of aging are employed, a year or more, often in oak barrels, to impart a lactic acid character to the beer. Special red malt is used to give the beer its unique color and often the matured beer is blended with a younger batch before bottling to balance and round the character.
Flanders reds have a strong fruit flavor similar to the aroma, but more intense. Plum, prune, raisin and raspberry are the most common flavors, followed by orange and some spiciness. All Flanders red ales have an obvious sour or acidic taste, but this characteristic can range from moderate to strong. There is no hop bitterness, but tannins are common. Consequently, Flanders red ales are often described as the most "wine-like" of all beers.