Almost 500 years ago, on April 23, 1516, two Bavarian dukes issued a decree that said that beer could only be made from three ingredients: barley, water and hops. This came to be known as Reinheitsgebot (purity ordinance) or the Beer PurityLaw. When it was written, however, the intent was not to keep beer “pure.”
Originally, this degree was meant to keep brewers from using more valuable grains, such as wheat and rye, from being used in beer making. Barley is harder to digest and was therefore not as desirable for use in food. You can read an English translation of Reinheitsgebot here.
While the original intent was to keep brewers from competing with bakers, after World War II when Germany was struggling to rebuild, it became a marketing tool. This seems to be the time when the Purity Law became more about marketing than natural resources. The American craft beer movement took this idea and ran with it; most industrial beer contains rice and other ingredients which craft beer makers and drinkers feel makes an inferior brew.
You may have noticed that there is a very important ingredient missing from the Purity Law. When it was written, the role of yeast in brewing was completely unknown. It wasn’t until the 1800’s that Louis Pasture discovered the role of microorganisms in fermentation.
The Reinheitsgebot was officially added to the Germain tax code in 1919 and remained in the tax code until 1987 when Germany joined the European Union.