The sight of what appears to be blood leaking onto a plate from a medium-rare steak can be off-putting. It’s one reason that steak is often overcooked, even though the trade-off is tough dry meat (and logically; cooked blood).
But the juices that come out are not blood at all.
Mammalian muscle requires oxygen to function, and typically this is transported to muscle by the blood stream.
Which is fine, until a large multicellular organism with claws and sabre-sharp teeth identifies you as a protein source. During your attempt to escape, blood flow cannot keep up with muscle oxygen demand, and you find yourself no longer at the top of the food chain.
That’s why muscle stores a reserve of oxygen in its tissue for emergencies (or breath-holding; think whales and seals). The oxygen is bound to a muscle protein called myoglobin. This protein contains iron, and it tints muscle red.
So the stuff coming out of a medium-rare steak is an iron-rich red protein juice.
Any actual blood in the steak was removed during the process of slaughter, rigor mortis and ageing that transformed the muscle into meat.