Some only use it as a marketing tool . The Reinheitsgebot ' says that beer is made of barley , so all wheat beers were not allowed by the original Reinheitsgebot ) . The vast majority of German breweries continue to comply with the Biergesetz , often claiming compliance with the Reinheitsgebot even when it is patently incorrect ( for example , for wheat beers , which were prohibited by the Reinheitsgebot ) , using this compliance as a valuable marketing tool .