When ground beef turns gray
By Martha Filipic
Ohio State University Extension
Sometimes when I open a package of ground beef, the meat has turned grayish brown on the inside. It smells OK, but it doesn't look very appetizing and I wonder if it's safe to eat. Is it?
Most likely, it's fine. Ground beef's bright red color comes from a pigment, myoglobin, which becomes red when exposed to oxygen (turning it into oxymyoglobin).
The plastic wrap covering the ground beef you see in the grocery store is permeable, allowing some oxygen to seep through and keep the meat on the exterior red. But ground beef that's not exposed to oxygen--like the meat that's on the interior--will often lose its red color after a few days.
However, if the ground beef is gray or brown throughout, it could be beginning to spoil. If you do detect an off odor or if the meat seems sticky or slimy, throw it away. Although bacteria that cause spoilage don't always cause illness, there's no sense in taking a chance.
Bacteria that can cause illness are really of more concern, but unfortunately they don't announce their presence through changes in appearance or aroma. Salmonella, E. coli O157:H7 (or other types of E. coli that produce Shiga toxin), Campylobacter jejuni, Listeria monocytogenes and Staphylococcus aureus have all been associated with ground beef and can cause severe illness, or even fatalities, especially in vulnerable people including children, the elderly or anyone who lives with a chronic illness. To minimize the chance that these bacteria could multiply and thereby increase the risk they could cause illness, be sure ground beef is stored at 40 degrees F or lower, cooked to an internal temperature of 160 degrees F, and otherwise handled properly.
Ground beef should be kept in the refrigerator--in the coldest part--for only one or two days before being cooked. Place it in the freezer for longer-term storage, but even there it can lose quality over time; it's best to use it within four months.
Use freezer paper or freezer-quality plastic bags to help prevent freezer burn--indicated by grayish-brown leathery spots on the surface. That's caused by air coming into contact with the food. Again, those spots aren't unsafe, but they'll be tasteless and chewy; you'll want to trim them away either before or after cooking.
The U.S. Agriculture Department has more information about safety and quality issues related to ground beef at http://bit.ly/grdbeef.