The Collaborative International Dictionary of English v.0.48:

Acerbate \A*cerb"ate\, v. t. [L. acerbatus, p. p. of acerbare,
   fr. acerbus.]
   To sour; to imbitter; to irritate.
   [1913 Webster]

WordNet (r) 3.0 (2006):

acerbate
    v 1: cause to be bitter or resentful; "These injustices
         embittered her even more" [syn: embitter, envenom,
         acerbate]
    2: make sour or bitter