To some it's the real deal, to others it's a bland brew. But thanks to a 500-year-old rule, everybody can be sure what's in German beer.

Only water, hops and malt are the permitted ingredients, according to the Bavarian beer purity law of 1516 that slowly spread to the rest of Germany. It's still on the books, albeit with some exceptions, today.

Chancellor Angela Merkel raised a glass of (alcohol-free) frothy brew to the law Friday at a ceremony in Ingolstadt, quoting Martin Luther's saying that "he who has no beer, has nothing to drink."

Critics say the so-called Reinheitsgebot — whose name suggests divine commandment — is little more than a marketing trick dreamed up in the early 20th century to keep foreign beers out of Germany.