>The origin is Spain, but the best ones in my
>opinion are Mexican-style and contain offal meats

Actually, the only palatable chorizos are the Spanish ones, which have been
unavailable in the U.S. until quite recently, and are still hard to find.
Central American and Mexico chorizos have a dry, acidic quality that isn't much
to recommend them.

As to the casing . . . don't expect an American chorizo to hold together
without it.

Neil