In addition, loose rewrapping dries out the meat's surface and allows it to absorb odors from other foods. For safety and better quality retention, Epley recommends leaving the original wrapping from the store intact if it is transparent plastic. The plastic used nowadays let oxygen in and prevent moisture from escaping. However, if the meat came from the store wrapped in paper, it should be wrapped again with plastic wrap. All fresh raw meat contains some surface bacteria put there during slicing and packing.
Low temperatures slow down bacterial growth.
Color is a good clue to the safety of raw beef, even ground beef, Professor Epley says. Cutting or grinding exposes the meat fibers to oxygeh which turns the meat bright red on the surface while the inside remains purplish red. After a few hours, ground beef takes on a bright red surface, a brown layer just below, and a purplish red core. The brown layer is due to oxygen infiltration and is harmless. If the meat is left out in the open, the purplish core will also turn bright red in about an hour.