What you see oozing out of your typical rare steak for example is primarily water mixed with the protein Myoglobin. It’s a common misconception that the juice is in fact blood. When the animal is slaughtered, almost all the blood is removed from the meat. The Myoglobin is used in the animals muscles to store oxygen much like what Haemoglobin does in the bloodstream.
In fact you can tell what’s a red meat and what’s a white meat by how much Myoglobin it contains. Animals with high levels of Myoglobin are considered “red meat” and those with low levels are “white meat”.
Source: Misconception Junction
Photo Source: The London Foodie