Why does ground meat sometimes stay pink when it has been cooked to an adequate endpoint temperature?
A Persistent pinkness in cooked ground beef patties is of considerable concern for food service establishments. Consumers view ground beef patties that are pink in the middle as being undercooked and unsafe when, in reality, these patties may be fully cooked and safe to eat. Persistent pinkness can be caused by reducing agents, pH, nitrite contamination, and/or carbon monoxide from gas ovens. Raw beef contains myoglobin, which combines with oxygen to form oxymyoglobin, which has a bright red color. Meat color is regulated (mostly) by a heme ring on the surface of the myoglobin protein. As myoglobin is heated, the protein will denature and unfold allowing oxidation of the iron molecule on the heme ring. Oxidation of the heme iron causes the formation of metmyoglobin, which is a cooked brown color. Reducing agents and the inhibition of oxygen reacting with the heme iron may keep the heme ring from oxidizing thus leaving a pink cooked color. When the pH value in beef muscle is greater tha
