The Bavarian Beer Purity Law (“Reinheitsgebot”) is a law that governs what ingredients can be used for beer made in Germany.
Many alcohol aficionados, particularly beer enthusiasts, will know about this already.
Even if you do know, though, do you know what the three main ingredients originally allowed are, and which was the fourth additional ingredient added to the permitted list in the late 1800s? And, do you know what the exceptions to the law are? See: Bavarian Beer Purity Laws .
To recognize the day, why not raise a toast with a German-brewed beer?