Fresh meat in the supermarket is red because of the pigment called “myoglobin,” which stores oxygen in muscle cells. But the red color of freshly cut meat is temporary since aging, cooking, and bacteria, all separate the oxygen from the myoglobin, turning the meat a brownish-gray color.

As meat ages and is handled or cut, proteins lose their ability to hold onto water. Over time, some water is released and myoglobin flows out with it, giving the liquid a red or pink color.

When carbon monoxide meets the myoglobin in the blood in meat, the reaction impacts the normal color-change process meat would go through when exposed to oxygen. The result is a bright red color that can stay for several weeks.

If the meat is not exposed to oxygen, it changes to a gray-brown hue. Freshly cut meat is pink-red due to the reaction of myoglobin with oxygen. It turns gray as myoglobin changes to metmyoglobin. Packaging (and exposure to carbon monoxide) enhances and prolongs the red color.

Beef that has gone bad will develop a slimy or sticky texture and smell bad or “off.” If beef develops a grayish color, that doesn’t necessarily mean it has gone bad. Don’t taste meat to determine if it’s safe to eat or not. Call the USDA’s hotline.

This darkening effect is due to the oxidation state of the iron atoms in myoglobin. When the myoglobin is exposed to oxygen, before you cook the meat, the iron atom oxidation level is +2 and it is bound to a dioxygen molecule (O2), which makes the meat appear bright red.

Answer: The steaks should be fine. As the U.S. Department of Agriculture points out, it’s normal for fresh meat to change color during refrigerator storage. For instance, it’s common for beef to turn more of a brownish shade, due to oxidation.

8 Simple Ways to Make Tough Meat Tender

1. Physically tenderize the meat.
2. Use a marinade.
3. Don’t forget the salt.
4. Let it come up to room temperature.
5. Cook it low-and-slow.
6. Hit the right internal temperature.
7. Rest your meat.
8. Slice against the grain.