I'm afraid that the
"Reinheitsgebot" specifically refers to
brewed beverages - so nothing that has undergone distillation or burning may called (rather: sold as a) Beer in Germany.
HOWEVER: The Reinheitsgebot dates back to 1516, a time when runes e.g. where long out of use in communities in the area that is now called Germany and beer-brewing traditions prior to 1516 were
considerably more diverse (There's even one modern exemption to the Rheinheitsgebot that uses sugar in the brewing process)
TL;DR - Anything with
runes on its cask could (reasonably) be assumed to pre-date the Reinheitsgebot by up to a Millennium (Also: It's either radioactive, or summons gibbering Horrors from the other side of space-time, remember? So even if it did follow the Reinheitsgebot, it could never be legally sold anyhow)
I'd say just screw the purity law, yes?
As to the "Wurmvater", there's:
*
Thallik Wormfather of the Elderscrolls online
oooooooooor (believe it or not)
* An actual, living German named Hans-Gerhard Starck out of Berlin-Schöneberg, who earned his nickname "Wormfather Starck" due to his habit of using specimens of the compost-worm
"Eisenia Foetida" to digest his organic Kitchen-waste. He has successfully converted 100 Berlin households to "worming" ...
(src) SCHÖNEBEBG - Bei Hans-Gerhard Starck hat die Müllabfuhr schon lange nichts mehr zu suchen. Seit 20 Jahren kompostiert der Schöneberger auf seinem Balkon auf originelle Weise Küchenabfälle. Dank des Kompostwurms "Eisenia Foetida", eines nahen Verwandten des Regenwurms. Mit Vorliebe verspeisen sie alle organischen Abfälle. – Quelle: http://www.berliner-kurier.de/18143056 ©2016
I leave it up to you which one you'd rather see in connection with something you want to pour down your gullet - the fictitious Necromancer, or the actual biological-waste-eating-worms-connaisseur. I guess the Wormfather would mostly be associated with death, corpses & compostation.
More interesting would be the "Totenkopfgeburtstag" (Skullbirthday): Most Germans would probably associate the picture of a skull with either "Warning: Poison" or the "Totenkopfflagge", i.e. the Jolly Roger.
There
is actually a famous German privateer, one
Klaus Störtebecker, with an interesting legend to him, or more specifically, to his execution:
The most famous legend of Störtebeker relates to the execution itself. Störtebeker is said to have asked the mayor of Hamburg to release as many of his companions as he could walk past after being beheaded. Following the granting of this request and the subsequent beheading, Störtebeker's body arose and walked past eleven of his men before the executioner tripped him with an outstretched foot. Nevertheless, the eleven men were executed along with the others.
Conveniently, Störtebecker pre-dates the purity-law by more than a century.
So your beverage should be something that could conceivably kill a strong man by blowing his head off
and cause his (headless) corpse to rise & go looking for a ship to run circles around.