The Collaborative International Dictionary of English v.0.48:

Munch \Munch\, v. t. & i. [imp. & p. p. Munched; p. pr. & vb.
   n. Munching.] [Prob. akin to mumble: cf. also F. manger to
   eat (cf. Mange), and m[^a]cher to cher (cf. Masticate).
   See Mumble.]
   To chew with a grinding, crunching sound, as a beast chews
   provender; to chew deliberately or in large mouthfuls.
   [Formerly written also maunch and mounch.]
   [1913 Webster]

         I could munch your good dry oats.        --Shak.
   [1913 Webster]