The Collaborative International Dictionary of English v.0.48:

Despumate \Des"pu*mate\, v. t. & i. [imp. & p. p. Despumated;
   p. pr. & vb. n. Despumating.] [L. despumatus, p. p. of
   despumare to despume; de- + spumare to foam, froth, spuma
   froth, scum.]
   To throw off impurities in spume; to work off in foam or
   scum; to foam.
   [1913 Webster]