"It's economic fraud," said whistleblower Gerald Zirnstein, a former scientist at the United States Department of Agriculture (USDA). "It's not fresh ground beef. It's a substitute, it's a cheap substitute being added in."
Zirnstein and fellow USDA scientist Carl Custer both warned against using what the industry calls "lean finely textured beef," also known as "boneless lean beef trimmings" (BLBT) and "pink slime." But their bosses overruled them.
Custer, a retired USDA microbiologist, told ABC News why he never considered it beef.
"Because it was a salvage product," said Custer. "Fat that had been heated at low temperature and the excess fat spun out."
The beef filler is waste trimmings that undergo a process to separate muscle from fat. The mixture is then sprayed with ammonia to kill bacteria, then added to ground beef as a cheaper filler.
The trimmings are approved by the USDA and do not have to be on listed on the label.
"Boneless lean beef trimmings (BLBT) is a safe, wholesome and nutritious form of beef that is made by separating lean beef from fat. These trimmings are USDA inspected. The beef trimmings that are used to make BLBT are absolutely edible. BLBT is a sustainable product because it recovers lean meat that would otherwise be wasted," American Meat Institute President J. Patrick Boyle said in a statement.
Many shoppers were concerned by the report.
"Anything should be left [on the label], then we can decide," said Orange resident Anita Singh. "Some people may say, 'Hey, I don't care, I'm still going to eat it.'"
"It gives you pause for concern when you don't know what's in there," said Orange resident Kurt Yusuf.
Last month, fast-food chains such as McDonald's said they would stop using "pink slime" in their ground beef.