With a little practice you can tell when your meat is done with the touch of your finger or tongs. As meat cooks, the proteins contained within it break down and recombine in a process called denaturing.
The texture of the various degrees of doneness of meat correspond closely to the feel of the fleshy part of your palm below the thumb: The more the meat is cooked, the less malleable it becomes. Try this finger test the next time you cook a steak and see how accurate your equipment is!
Rare
Touch your thumb and forefinger together and press on the fleshy part below your thumb (illustrated in the red circle in the photo) -- it should feel soft to the touch with your other forefinger and a little bouncy. This is how a rare steak feels.
Medium
Well Done
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