Myoglobin is a heme protein responsible for transporting oxygen in the muscle cells of animals. Structurally similar to hemoglobin in blood, myoglobin binds oxygen molecules and stores them in muscle tissue, aiding in muscle metabolism and endurance. This protein is also the key factor behind the redness seen in meat.
Myoglobin’s primary function in muscle tissues is to store and release oxygen when needed, especially during periods of muscular exertion. Its concentration varies with the type of muscle and the animal’s activity level, meaning muscles used more frequently for movement tend to have higher myoglobin levels, contributing to darker meat.
As steak cooks, myoglobin undergoes several transformations. In raw meat, myoglobin is in its natural state, appearing red. As the meat reaches medium levels of doneness, the myoglobin’s iron atoms oxidize, turning brownish, which is why well-done meat has a more browned appearance. Rare steak, being cooked to a lower temperature, retains its reddish myoglobin-rich juices.
