Reinheitsgebot

The Reinheitsgebot is a German beer purity law from 1516. It is one of the oldest consumer protection laws still enforced.

The most famous provision of the law is ". . .the only ingredients used for the brewing of beer must be Barley, Hops and Water." Yeast is not mentioned, mainly because no one had discovered it. Notice that wheat is missing. This law limited what could be used for brewing and kept wheat in the hands of the bakers. It wasn't until the 17th century that the German aristocracy was given special permission to make wheat beer.

The Reinheitsgebot does limit the styles of beer that can be produced. In Belgium, for example, practically every brewery has its own style. The Reinheitsgebot also restricts most American beers, which use corn and/or rice in their formulation to lighten the body of the beer.

It's all well and good to only brew according to the Reinheitsgebot, but you're missing out on a whole world of beer flavors.