I understand that the meat is thinned with a mallet before coating with breadcrumbs and frying.
What parts of veal or pork are suitable?
(Googling the subject seems to produce mostly sausage related hits for some reason)
The real, original Wiener Schnitzel is veal. Definitely. I can't link to a web source now, but I have some German cook books at home, including one solely about different kinds of schnitzel.
From the veal, you use parts 6, 7 and 11 for any kind of schnitzel, 7 being the best and highest-prized choice. I don't know the English names, maybe somebody can supply them. Also, try using leaner meat. I think that in the US, the fat marbled beef is considered higher quality. But in Europe, lean beef is preferred. A good beef schnitzel has maybe 3% fat.
This said, there are lots of places which cook pork schnitzels in the Wiener style and call them Wiener Schnitzel. It isn't traditional, but if you like the taste, there is nothing against doing it that way at home. They come from the same parts of the pig as the veal schnitzel: the ham and the lower back. Again, they should be very lean. And in both cases, unlike a steak, a schnitzel is always boneless.
When you see 'Wiener Schnitzel' on a german or austrian menu it is ALWAYS veal. Schnitzel made with pork loin can not be offered as such in restaurants, but must be called instead "Schnitzel Wiener Art"(Vienna Style). Here is a tip for those schnitzel lovers out there:use japanese panko bread crumbs for your coating!
German Food Guide says to use the pork loin.
Cooks.com says to use either a pork chop or a veal cutlet.
I was taught that the "Wiener" referred to the original recipe origins in Vienna. This Schnitzel in the Vienna style was originally veal.
American German restaurants usually serve a variety of meats prepared into paillards (flattened with mallet) and breaded - generally only the Veal one is called "Wiener Schnitzel".
At home, I prefer to use Center Cut pork chops to prepare what I like to call "Swiner Schnitzel". I agree with the answer above that leaner is better. Schnitzel cooks extremely quickly and marbling is unnecessary.
I’ve not the points to comment on rumtscho‘s post, but this is an extension of what he said.
With regards to pork:
Using the loin is a nice and quick way. Just slice (butterfly cuts are good) and prepare them. In my opinion the flavor is good but not great. It never puts my back in Mittelfranken, Oberbayern, or any part of Germany for that matter. With sirloin, the flavor was dead on, but the fat running through it, made for a pour consistency and wasn’t nice to work with. Pork Tenderloin lacks circumference and makes small schnitzels, but flavor and consistency are there.
I believe the top-round is the best cut for large, tasty, and consistent cuts, but alas I have not used it. At some point, I’ll pick up a raw ham and cut the top-round from it. I have no idea where, in America, you can buy the round already cut out. I’d likely use the bottom and eye of round for stew… or perhaps additional smaller schnitzels.
Tip: though oil of your choice works, using butterschmalz (Clarified butter) ads some really nice flavor. I found some clarified butter called Ghee at a store here, however you could make your own. Regardless, not needed, just a nice touch.