According to Duden, Kaltschale is a kind of soup that is served cold. "Hopfenkaltschale" could therefore be translated as "cold hops soup".
It is a name occasionally used to jokingly refer to beer.
There is even a Duden entry for Hopfenkaltschale, confirming this usage ("umgangssprachlich scherzhaft" - colloquial and jokingly) and frequency (low).
Whether beer is actually vegan depends on the applied definition of vegan (consider ingredients only or other components used in the production process, such as catalysts or filters) and the specifics of the production process (but such details are usually glossed over anyway when joking).