Here's a copy of his official message to the Legislature. (Sorry the copy is crooked.) The gov doesn't really get going on his reasons for the veto until the bottom of page 2.
As Richardson points out, this is his final action on any legislation -- at least barring any unforeseen special session. At his news conference this morning Richardson said he sees no need for a special session.
Veto Message Food Tax
Veto Message Food Tax