The Collaborative International Dictionary of English v.0.48:

Multum \Mul"tum\, n.
   An extract of quassia licorice, fraudulently used by brewers
   in order to economize malt and hops. --Craig.
   [1913 Webster]

   Hard multum, a preparation made from Cocculus Indicus,
      etc., used to impart an intoxicating quality to beer.
      [1913 Webster]