I don't know German, but it seems to me that you forgot the yeast...
Yeast is never mentioned in Reinheitsgeboot, the German Purity Law of 1516 because they didn't know it existed. All they knew is you mix, Barley, Hops and Water and you let it sit and after a period of time you get this wonderful thing called beer. Yeast was not discovered until the 1800's.
German Beer Purity Law from 1516
"How beer should be served and brewed in summer and winter in the principality"
"Herewith, we decree, order, express and wish, together with the Privy Council, that from this day forth everywhere in the Principality of Bavaria, in the countryside as in the towns and marketplaces, wherever no other specific ordinance applies, from St. Michael's Day until St. George's Day a measure or head of beer shall not be sold for more than one pfennig Munich currency and from St. George's Day until St. Michael's Day a measure shall not be sold for more than two pfennigs of the same currency, nor a head for more than three haller. Violators of this decree shall be punished as prescribed below. Whoever should brew a beer other than Maerzen, is forbidden, under any circumstances, to serve or sell a measure for more than one pfennig. We especially wish that, from this point on and everywhere in the countryside as well as in the towns and marketplaces, nothing is to be added to or used in beer other than barley, hops and water. Whosoever knowingly disobeys this decree will be severely punished by the court having jurisdiction over him by having his barrel of beer confiscated whenever this offense occurs. Whenever an innkeeper buys beer at the prescribed price from any brewery in the countryside as well as in the towns and marketplaces, he is allowed to resell it privately to the lowly peasantry for one haller more than the price of the measure or head of beer stipulated above."
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