If you’ve ever gagged at the thought of a “bloody” steak, you might want to give medium-rare a second try. That red liquid isn’t blood.
Practically all of the blood is taken out of meat during slaughter, according to the Food and Agriculture Organization of the United Nations. If that red juice were blood, even poultry would have that rosy color.
The red hue comes from a protein called myoglobin, which helps muscle tissue store oxygen like hemoglobin does in your blood. And like hemoglobin, the iron in myoglobin turns red when it binds with oxygen, giving raw meat that red hue. Most mammals have high amounts of myoglobin in their tissue, which is why they’re known as “red meat.” Learn what happens when you give up red meat.
Once you throw that fresh steak on the grill, though, the heat changes myoglobin’s chemical structure, and the food turns from red to brown. When steak is red and done rare, it hasn’t lost its moisture. But heat squeezes those juices out, so by the time the meat turns brown, that well-done steak also isn’t as tender.
As it loses its freshness, even uncooked meat will start turning an unappetizing shade of gray-brown when it’s exposed to air. That’s why some meatpackers treat raw steak with carbon monoxide, which prevents it from interacting with oxygen, according to the World Health Organization. As a result, the meat holds on to that rosy color—and makes you more likely to buy. Meanwhile, cured meats like hot dogs get a nitric oxide treatment to keep them looking pink.