You bring home a package of ground beef from the grocery store. From the outside, everything looks perfectly normal: the meat is bright red, fresh-looking, and exactly what you expected.
Then you open the package.
As you separate the meat, you discover something surprising. While the outside is red, parts of the center are grey, brown, or even slightly purplish.
The first thought many shoppers have is immediate:
Did the grocery store hide old meat underneath the fresh-looking red layer?
It’s an understandable reaction. We have been conditioned to associate bright red beef with freshness and brown or grey beef with spoilage.
But meat color is more complicated than it appears.
In many cases, ground beef that is red on the outside and grey or brown in the middle has not been secretly replaced with old meat. The difference can happen naturally because of oxygen and a protein found in
