Reminder: the Reinheitsgebot, or Purity Law for brewing beer promulgated by two German Dukes in 1516, was long before the germ theory was dreamed of. That kind of purity was the all-natural kind, of no chemicals or modern experiments, beloved even today and derived from Germanic paganism. The Germans have a bit more fascination with purity than average, leading to the development of heroin by getting all the harmful impurities out of morphine, and er, tribal favoritism leading to The Holocaust.
Maybe those are better beers, but I wouldn't expect magic, y'know? Purity has several meanings.