Myoglobin: Why Meat Is Red (and It's Not Blood)
Myoglobin is a protein in muscle that stores oxygen, using an iron atom at its core. It's the main reason meat is red, and the red juice that pools under a steak is water coloured by myoglobin, not blood.
Why some meat is redder
Muscles that work hard for long periods need more stored oxygen, so they're packed with more myoglobin. Beef and lamb are red; pork is pink; chicken breast is pale; chicken thighs and duck are darker. Older animals and active muscles have more.
The colours of raw meat
The iron in myoglobin changes colour depending on what it's bound to:
| Form | Colour | When you see it |
|---|---|---|
| Deoxymyoglobin | Purplish red | Vacuum-packed meat, freshly cut interiors |
| Oxymyoglobin | Bright cherry red | Surface exposed to air for 15–30 minutes |
| Metmyoglobin | Brown-grey | After days of oxygen exposure, or at low oxygen |
So a vacuum-packed steak that looks dark purple will "bloom" red after you open it. A brownish centre in a pack of ground beef is usually just oxygen-starved, not spoiled. Judge spoilage by smell, slime and the date.
What happens when you cook it
Heat denatures myoglobin, changing its shape so it can no longer hold the red colour. That's why doneness looks the way it does:
- Rare, about 50–52 °C / 120–125 °F: most myoglobin intact, deep red centre.
- Medium, about 60–63 °C / 140–145 °F: a lot of it denatured, pink.
- Well done, 70 °C / 160 °F and up: almost all converted to grey-brown.
Colour is not a safety test
Myoglobin can mislead you. Ground beef that was stored with oxygen can turn brown inside well before it's safe, known as premature browning. Other meat can stay pink when it's fully cooked, especially if it's very fresh or high in pH. Smoked meats and cured ham stay pink because smoke gases or nitrite lock myoglobin into a heat-stable pink form, which is how a barbecue smoke ring forms.
The only reliable test is a thermometer: 71 °C / 160 °F for ground beef and pork, 74 °C / 165 °F for poultry.
Questions
Is the red liquid in a steak blood?
No. Almost all blood is drained at slaughter. The red liquid is water coloured by myoglobin, the oxygen-storing protein in muscle.
Why is ground beef brown inside the package but red on top?
The surface touches oxygen and forms bright red oxymyoglobin. The inside, cut off from air, stays as purplish deoxymyoglobin or turns brownish metmyoglobin. It's normal and not a sign of spoilage on its own.
Can I judge doneness by colour?
Not reliably. Ground meat can brown before it reaches a safe temperature, and some meat stays pink after it's fully cooked. Use a thermometer: 71 °C / 160 °F for ground beef and 74 °C / 165 °F for poultry.
Why is chicken breast white but thighs dark?
Leg muscles work constantly and need more oxygen, so they hold more myoglobin. Chicken breast muscles are used in short bursts and contain very little.