After avoiding the "pink slime" controversy for the most part, Chicago Public School officials are now admitting that students may have been served the slime, which is made from ground beef trimmings and cartilage, and treated with ammonia or citric acid.

The Chicago Tribune reports that when CPD officials denied using the processed beef product -- referred to as "lean finely textured beef" in the meat industry -- they were not aware that beef from Don Lee Farms in California may have contained the substance.

The district has since severed ties with the company, and removed all the "pink slime" from its schools and warehouses.

"We gave the best information we had at the time, and it was accurate from what we knew," CPS spokeswoman Robyn Ziegler told the Tribune. "It's very possible that none of the (chemically treated) beef had been delivered to CPS. But in order to eliminate any doubt about that we eliminated the delivery of that beef to our schools."

Though "lean finely textured beef" was used by fast food restaurants for years, many decided to scrap the product after a scathing 2009 article about the beef in the New York Times. Celebrity chef Jamie Oliver has also railed against "pink slime," but parents and students caught on when an online petition about the product circulated in early March.

“We’re taking a product that would be sold in its cheaper form for dogs,” Oliver said on his show “Food Revolution." “After this process, we can give it to humans.”

The beef industry has defended the product as safe for consumption.

"LFTB has created affordable nutrition for kids," Eric Johnson, spokesman for the Illinois Beef Association, told WGN News. "Having beef [in a student's] diet is maybe the best well-balanced meal they're liable to get that day."

Houston resident Bettina Siegel, whose blog "The Lunch Tray" focuses on kids' food, started the online petition on March 6 asking Agriculture Secretary Tom Vilsack to "put an immediate end to the use of `pink slime' in our children's school food," the Associated Press reported.

"That's what upset me. This idea that children are passively sitting in a lunch room eating what the government sees fit to feed them and McDonald's has chosen not to use it, but the government is still feeding it to them," she said. "That really got my ire."

Ziegler told the Tribune that CPS was taking steps to keep "pink slime" out of the school system from here on out.