Until the 15th Century, it was common in Germany, particularly in Bavaria, to use rye malt for brewing beer. However, after a period of bad harvests, it was ruled that rye would only be used for baking bread, (thus only barley was to be used for beer, see the German law known as the Reinheitsgebot). Roggenbier virtually disappeared for almost five hundred years. In 1988, it reappeared in Bavaria.
The modern version of roggenbier is typically about 5% ABV and is fairly dark in colour. The flavour is grainy, often having a hearty flavour similar to pumpernickel bread. Typically, at least 50 percent of the malts used to make the beer are made from rye. Source: Wikipedia