When it comes to raw beef and pork, the color red usually means fresh -- but there is a chance that meat may be lying about its age.
Shoppers who think they can spot older meat may be getting outsmarted by a secret science -- using carbon monoxide to keep meat looking red and fresh.
The carbon monoxide binds with a protein in the meat, keeping it red -- though not necessarily fresh -- for weeks.
"It tends to deceive the consumer into thinking they're buying something fresh when they are not," said Donna Rosenbaum of the group Safe Tables Our Priority.
The gas will keep raw meat red for weeks. The meat industry says color is never the best way to judge meat anyway.
"We don't believe color should be used as the only indicator of quality and freshness, and it's certainly not an indicator of safety," said Randy Huffman of the American Meat Institute.
Even perfectly good meat quickly turns brown when it's exposed to oxygen. The amount of carbon monoxide that meatpackers are putting in prepackaged meat is safe, but they are not telling the public.
"What this packaging technology allows us to do is protect the color," Huffman said. "To maintain the red color consumers are used to purchasing."
In a demonstration supplied by a company with competing technology, untreated meat turned brown after eight days and treated meat maintained the red color. But both were growing E. coli.
"So we're worried that potentially you could have product that has this high pathogen load and that somebody won't know it because they'll perceive it to be fresh," Rosenbaum said.
The industry says that consumers can rely on the sell-by date on the package, and that the process is well-studied and safe. However, some food-safety advocates point out that the practice is banned in Europe, and they want the U.S. government to take a harder look.
"We really want to see some safety nets put into this system so that this product is not unleashed on unsuspecting American consumers," Rosenbaum said.