WITH films, exhibitions and a commemorative stamp, Germany is marking the 500th anniversary on April 23rd of an event considered central to the national identity. It is not Martin Luther’s nailing of his 95 theses to a church door in Wittenberg—that anniversary falls next year. Rather, it is the passing of a law concerning beer by two Bavarian dukes, Wilhelm IV and his brother Ludwig X. Henceforth, they decreed, brewers in Bavaria were to use only three ingredients: water, barley and hops. (They did not yet know about yeast, which occurs naturally in beer but was officially permitted as an additive only later.)

Subsequently dubbed the Reinheitsgebot, or “German beer purity law”, the regulation spread. Otto I, a Bavarian prince who became king of Greece in the 19th century, subjected his new country’s brewers to its stringent rules (becoming perhaps the first German to impose austerity on the Greeks). Other German regions adopted it after unification in 1871, and from 1906 the whole of Germany did. Today the Reinheitsgebot—which governs lagers but is more relaxed for top-fermented ales—is in effect a marketing tool for the country, a liquid extension of “Made in Germany”.

But the purity law was always an impostor. True, nasty things could be found in 16th-century swill, from traces of chalk and pitch to ox gall. But the primary purpose in 1516—as with many regulations today—was market-rigging and protectionism. By excluding wheat and rye in beer, the law aimed to keep grain prices low for bakers. It also kept out northern German and foreign beers that contained other ingredients. (That bit, at least, has been rectified: in 1987 the-then European Economic Community ruled that brews produced abroad and not compliant with the purity law may be sold as beer in Germany.)

The law’s real victim is variety. Germany makes some fantastic beers, of course. Connoisseurs such as Johannes Tippmann, a scholar of brewing at the Technical University of Munich, reckon that more than 3,500 different compliant beers are made today, and more than 1m variants could be made just by tweaking the mineral content in the water, the type of yeast and so forth.

But the prevailing view is that the purity law has stifled German beer innovation. Nimble craft breweries in California and makers of lambic beer in Belgium—fermented by exposure to local and wild yeasts and bacteria—have left the Germans in the foam. While foreigners can experiment with spices, fruits and much else, most of Germany’s 1,388 breweries must stick to their four traditional ingredients if they want to call their product “beer” (as opposed to, say, “alcoholic malt drink”).

That helps explain why Germans are increasingly turning to wine. At reunification in 1990, annual beer consumption per head was 148 litres. By last year it had fallen to 106. The Oktoberfest may still be the quintessential German party. But it’s not the beers that make it exciting.