Cooking science

Myoglobin colour states

The red in meat is not blood. It is myoglobin, a protein that stores oxygen in muscle, and its colour changes with oxygen, with acidity and with heat. Understanding it is mostly useful for knowing when not to trust what you are looking at.

Not blood

Blood is drained at slaughter and very little remains in a retail cut. What you see is myoglobin held inside the muscle cells, and the red liquid in the bottom of a package of steak is myoglobin dissolved in water, not blood.

How much myoglobin a muscle contains depends on how much sustained work it does. That is why beef is darker than pork, why chicken thigh is darker than breast, and why the same bird has both — legs work continuously and breast muscle is used in short bursts.

The colour states

Purplish-red

Myoglobin with no oxygen attached. What you see in vacuum-packed meat, and in the middle of a thick cut.

Bright cherry red

Oxygen has attached at the surface. This is the colour of freshly cut meat exposed to air, and it develops within minutes — "blooming".

Brown

The iron in the myoglobin has oxidised. Happens naturally over a day or two in the fridge and is not in itself a sign of spoilage.

Grey-brown when cooked

Heat has denatured the protein permanently. This is the change you see through a cooking steak.

Pink despite thorough cooking

Several causes — nitrites in cured meat, gases from a barbecue or gas oven, or the natural pinkness near poultry bone, especially in young birds.

Why colour is not doneness

This is the practical point. Cooked meat can stay pink for reasons that have nothing to do with temperature, and meat can turn brown before it is cooked through — frozen and thawed mince is a common case.

Cured meats stay pink permanently because nitrite locks the myoglobin into a stable pink form. Meat cooked over charcoal or in a gas oven can form a pink ring near the surface from gases in the atmosphere. Very fresh poultry, and poultry frozen young, often stays pink around the bone.

So colour tells you about chemistry, not about whether food is cooked. Where cooking matters for safety — poultry, minced meat, pork, stuffing, reheated leftovers — the only reliable answer is a temperature measured with a thermometer, against the guidance of a food-safety authority. FoodHQ does not publish safe internal temperatures; the Food Standards Agency does, and that is where to look.

Practical points

• Brown patches on mince in a sealed pack are usually just the parts that had no oxygen. Smell is a far better guide than colour.
• Meat that smells sour, feels slimy or tacky, or looks green should be thrown away regardless of colour.
• For a good sear, dry the surface. Wet myoglobin-rich liquid on the surface has to boil off before browning can start.
• Resting meat lets the liquid redistribute, so less runs out on the board. See resting and redistribution.
• Grey steak is a cooking problem, not a meat problem: the pan was not hot enough, or the meat was crowded.

Common questions