A former USDA scientist is blowing the whistle on ‘pink slime’, a concoction of leftover beef scraps and connective tissue treated with ammonia hydroxide that’s commonly added to ground beef.

“It’s economic fraud,” microbiologist Gerald Zirnstein told ABC News. “It’s not fresh ground beef. … It’s a cheap substitute being added in.”

Invented by the company Beef Products Inc, the process involves grinding together connective tissue and beef scraps normally used to make dog food.  Cooked at low heat and then centrifuged to separate out the meat, the mixture is treated with ammonia hydroxide gas to kill any pathogens like E. coli or salmonella, and then packaged into bricks, frozen and shipped out to grocery stores. And schools.

While Burger King, McDonald’s and Taco Bell have all declared that they are no longer using ‘pink slime’, 70% of ground beef sold in grocery stores contain the mixture, and the USDA just purchased 7 million pounds of it for school lunches.

‘Pink slime’ recently gained notoriety after Jaime Oliver, celebrity chef and healthy school food advocate, featured a grisly demonstration of its manufacturing process on his show, Food Revolution, for a group of horrified parents and students.

The president of the American Beef Institute says that this product, known in the industry as Boneless Lean Beef Trimmings, is “absolutely edible” and a press release from the group calls it “a sustainable product because it recovers lean meat that would otherwise be wasted.”

But Carl Custer,  a 35 year veteran of the Food Inspection Safety Service who objected to the approval of this meat-like product back in the 1990’s, says,  “It’s more like Jell-O than hamburger, plus it’s treated with ammonia, an additive that is not declared anywhere.”

Since the beef industry considers the mixture to be meat, any beef product containing the mixture does not have to be labeled.