What is the German Beer Purity Law? | Made in Germany

In 1516, Duke Wilhelm IV of Bavaria decreed that beer should only be brewed from barley, hops and water. This purity law brought German brewers worldwide success. But 500 years on, some rebels are trying to add more variety and new ingredients to German beer.
For more information and videos go to:
http://www.dw.de/program/made-in-germany/s-3066-9798