The German Purity Law "Das Reinheitsgebot"

German brewers have long boasted about their unique brewing method governed by the “purity law” (Reinheitsgebot, actually translation is - “purity decree”). This decree was first proclaimed in 1516 by the Bavarian Duke, Wilhelm IV in the town of Ingolstadt (the home of Audi, the car manufacturer). Although, in different part of the then German Kingdom (Prussia and other parts including Bavaria), decrees on the ingredients for making or brewing beer were in-place and applied only to that particular local area, city or region. When introduced in 1516, the Bavarian beer purity decree was the first to apply to the entire German kingdom or principality.

The Reinheitsgebot was until 1987 part of the German law and also the oldest food quality regulation in the world remaining in force. Germany, as a member of the European Union (EU), was forced by a court decision to change the law in order to allow free trade of goods between itself and the rest of the EU member states. 

Non-German brewers viewed the "Reinheitsgebot" as a form of protectionism for German breweries. Since 1993, a new, more liberal German beer law has been in effect, nevertheless, many, about 98% of German brewers still abide by the Reinheitsgebot, which dictates that beer may contain only three ingredients: water, barley, and hops. (Yeast, a key ingredient in the beer-brewing process, was not discovered and introduced until after 1516.) When Bavaria joined Prussia to became part of Germany in the unification of 1871, one of the conditions was that the Bavarian beer purity decree apply to all of Germany.

Critics of the old German beer purity law liked to point out that the Reinheitsgebot in itself did not guarantee a good beer, and that it limited the types of beers that could be brewed and sold, for example, the "Weizenbier, and most dark beers" were technically in violation of the purity code. They also point out, correctly, that the original 1516 Reinheitsgebot was in reality more of a bread bakers protection law than a beer law, reserving wheat and rye strictly for bread. However, the Reinheitsgebot  did serve to keep German beer from being adulterated with other ingredients often found in non-German beer.