500 Years of the Purity Law for Beer On April 23, 1516, the Bavarian dukes Wilhelm IV and Ludwig X issued in Ingolstadt one of the few laws that was to exist for centuries beyond that time. The Purity Law for Beer still defines not only but chiefly the German art of brewing and is considered the oldest food products law in the world still in existence and in effect. Its origin can be found in the Landshut Succession War of 1504/05 ("Bavarian Feud"), which led to the reunification of the Bavarian dukedom fragments. This resulted in the need to harmonize the Bavarian state laws that finally led to a new state ordinance for all of Bavaria. A component part of this new ordinance was the "Bavarian Purity Law". In addition to the regulation of beer prices (which naturally changed over the course of time), every part of the purity law remained largely in effect up to the current times. The purity law dictated the exclusive use of barley, hops, and water in the brewing of beer. In the original text, it was formulated as follows. "We especially want that forthwith everywhere in our cities, towns, markets, and in the countryside no other parts than exclusively barley, hops, and water be used and employed for any beer." This text was changed many times in the past five centuries. Barley mutated to barley malt, later simply malt. The limitation to barley initially served to eliminate food shortage. Wheat was supposed to be used only to make bread. Finally, years later the limitation to barley was abandoned in favor of other types of grain. A fermentation process such as for beer production naturally also requires an initiator, but at that time, it was not yet mentioned. At least impurities with fungal spores leads in most cases to the desired success. Louis Pasteur (1822–1895) was the first to describe that the starting of a fermentation process is caused by a substance consisting of microorganisms (yeast) that consist of a multitude of single-cell fungi. Hence, since the 19th century beer can be brewed with the following: malt, hops, yeast, and water.