Originally enacted in 1497 by Albert IV Archduke of Bavaria & went on to cover all of Bavaria by 1516 as the borders of the Duchy changed. Whilst not the world’s oldest food purity law, it was the oldest continuous surviving food law upto modern times. Originally not so much a beer law, but a way of keeping the price of bread down by freeing up wheat & rye for bakeries.
Literally meaning "purity law", Reinheitsgebot dictated that the only ingredients to be used in the making of beer were; Water, barley & hops. Yeast was not known to be the active organism that converts the sugary wort into the finished alcoholic product until Louis Pasteur studied it in the 19th century.
As part of the conditions for joining German unification in 1871, Reinheitsgebot was enacted across the newfound country.
In 1952 the Reinheitsgebot was incorporated into the Biersteuergesetz (beer duty act), which said that beer made of other than barley, hops, water & yeast could not be marketed as "bier" in Germany. In 1988, the law was challenged successfully by the EEC - the forerunner to the EU - as being anti-competitive amongst European members. However this didn't apply to German breweries, who still were compelled to comply with the purity law.
Shortly after German reunification in 1990, the act was contested by a former East German brewer to allow maize, rice, sugar - any food ingredient - to be added to beer.
Many German brewers still advertise as remaining true to the Reinheitsgebot as a symbol of tradition.
The original Reinheitsgebot translated into English:
“We decree that set and want the advice of our landscape that henceforth everywhere in the Principality of Bavaria, in the countryside as well as in our cities and markets who have no special order it from Michaelmas (29 September) to Georgia (April 23, ) a measure or head of beer for no more than a penny Munich currency and Georgi to Michaelmas, the measure of not more than two Pfennig of the same currency, the head for not more than three Heller (usually half a penny) services mentioned above may result in sanctions bottom punishment should be given and served.
Where, however, a non-Märzen but another beer brew or would have otherwise, he shall by no means higher than a Pfennig and sell the measure. In particular, we want henceforth to be at no more pieces than beer alone barley, hops and water used and needed in our cities, towns and demLande everywhere.
Who knowingly transgresses this our warning and failure to comply with the will of his court authority to punish this draft beer, so often it occurs, will be taken away relentlessly.
Where, however, an innkeeper from a Bierbräu in our cities, towns or on demLande one, two or three buckets (containing about 60 liters) buys beer and again ausschenkt to the common peasants, to him alone and no one else is allowed and be without hindrance, the measure or a penny to give head beer expensive than prescribed above, and pour out.
We too should be reserved as sovereigns, in the event that lack and increase in grain would create severe hardship after the vintages also the area and the maturity periods are different in our country, for the general benefit to enact restrictions on how these things on the conclusion about is expressed and put the sale in detail."