The Red Juice in a Rare Steak Is Blood

That red liquid is not blood. When an animal is slaughtered, the blood is drained out, and very little remains in the muscle you buy as meat. The red juice in a steak is mostly water mixed with a protein called myoglobin, which lives in muscle tissue and stores oxygen, and it happens to be deep red, especially in red meats. Myoglobin is also why a steak changes colour as it cooks: heat alters the protein, so the meat goes from red to pink to brown. It is the same reason chicken and pork, which have far less myoglobin, look pale, while beef looks red. So 'bloody' steak is a misnomer; you are looking at muscle juice, not blood. The supermarket even tends to call it 'purge'. None of which makes a rare steak less delicious, but it does mean ordering well done to avoid 'blood' is avoiding a protein that was never blood in the first place.