Fast food meat contains 12% ammonia-treated scraps.

From ABC News:

How much meat is in your Taco Bell taco filling? How much is in your McDonald's Quarter Pounder or your Burger King Whopper? And is this meat really meat--or something else?

These questions took center stage in January when a California woman sued Taco Bell, claiming its taco filling is only 35 percent ground beef. The rest, she alleges in her class action suit, consists of edible padding: binders, extenders, preservatives, additives and other non-meat ingredients. Taco Bell says not only is its filling 88 percent ground beef, but that this beef is no different from what you'd buy at your local supermarket for use at home. The company has fought back with a counterattack ad campaign. Where's the truth?

Kantha Shelke, chief science officer of Corvus Blue LLC, a Chicago food science and nutrition research firm, says it's frankly impossible for a consumer to know how much meat is in a food item at Taco Bell, McDonalds, Burger King or any other fast food restaurant. That's because such disclosure is not required. Even when an item is touted as being "all-beef," it may be only 70 percent meat and not run afoul of regulations.

Non-meat ingredients in meat items include ones that add flavor or promote consistency, and binders. "American consumers think they're being cheated out of their money when they hear that term," says Shelke. "But logically speaking, binders are a very natural thing. They prevent water from coming out during cooking. When you make meatloaf at home, you use breadcrumbs for the same reason—to hold the moisture."

As for the meat itself, some of it can be…well, not exactly what you think of when you think of meat.

Bill Marler, an plaintiffs' attorney specializing in food safety lawsuits, says that it's common for up to 10 percent to 12 percent of that juicy burger you're about to pop into your mouth to be "ammoniated beef product"—scraps and trimmings left over from slaughter that used to be relegated for use in pet food.

They no longer are, thanks to a treatment process that uses ammonium hydroxide to protect meat made from scraps against bacterial contamination, thus rendering it fit--at least according to regulators--for human consumption.

The product is produced by Beef Products Inc. of South Dakota, whose website says that if you're eating a hamburger in a "quick-service restaurant" (the food industry's preferred term for fast food), "...chances are you'll be eating product produced by BPI."