“Lean finely textured beef,” aka “pink slime,” sparked an uproar when the USDA bought 7 million pounds of the stuff for school lunches. The agency maintains it’s safe and healthy; critics say it’s not fit to eat. But the burger filler isn’t new, nor is it the only way that meat packers maximize production. Here’s how it stacks up against two other mechanical processes.

Lean Finely Textured Beef -  What does it look like?

What else is it called? “Pink slime,” coined by former USDA microbiologist Gerald Zirnstein in 2002.

What is it? Processed beef trimmings and recovered materials from meat carcasses, like fat and connective tissue.

How is it made? Trimmings are heated to 100°F and spun inside a centrifuge to separate the meat from the fat. After the fat is removed, the remaining beef bits are treated with ammonia hydroxide to kill bacteria such as E. coli or salmonella. They are then ground up, frozen into blocks and added to other beef products.

How is it labeled? Some companies may soon include “lean finely textured beef” on their product labels, and Congress recently introduced a bill to require labeling. Right now the USDA does not require any disclosure, because the product is considered the same as beef.

Health concerns? Trimmings are typically collected from more bacteria-prone parts of the cow, but treatment with ammonia is supposed to kill pathogens. In 2009 some beef products have tested positive for E. coli and salmonella, but the USDA says it has modified inspection processes since then to address safety concerns. The USDA continues to “affirm the safety of Lean Finely Textured Beef product for all consumers.”

Read the rest of the ProPublica report and learn about “mechanically separated meat” and “advanced meat recovery” here.