Gamp's Old Gregarious was a wizarding brand of beer, created by the landlord of the Leaky Cauldron in the early 18th century. The beer is named after Ulick Gamp, first Minister for Magic, who decreed that the Leaky Cauldron could remain in operation after the passing of the International Statute of Wizarding Secrecy provided it conceal its existence from Muggles and its patrons maintain good behaviour.
Gamp's Old Gregarious is noted to be particularly disgusting. There is a one-hundred Galleon prize at the Leaky Cauldron for anyone who manages to finish a pint of it, a feat that had yet to be accomplised by 2014, about three-hundred years after its creation.
- Pottermore (Mentioned only)