Contrary to what some shoppers suspect, the outside of the meat is not redder than the inside because the butcher treated it with a chemical spray. Mother Nature, not the meat monger, is responsible. When an animal dies, its heart stops pumping oxygen-rich blood to the various muscles. Denied that oxygen, the myoglobin protein in the muscles loses its bright red pigmentation and acquires a purplish, and then brownish, tinge.
Another color change starts to occur when the meat is butchered into retail cuts and wrapped in porous plastic film, giving the meat's newly exposed surfaces access to the oxygen in the air. As the meat sits in the refrigerated display case, oxidation finishes turning the myoglobin on the meat's exposed surfaces bright red. (Butchers refer to this color development as "bloom.") So, though the outside of the meat is the shade of red that consumers are taught to look for, the inside remains brown simply because the unexposed myoglobin lacks enough oxygen. If you cut open the meat and give it time to aerate, the new surfaces should become bright red.