Meat isn't always bright red because its colour depends partly on how a muscle protein called myoglobin interacts with oxygen. Fresh beef can look dark purple in a vacuum pack, then turn cherry red when exposed to air. Butchers call this change “blooming”.
Watch: Why isn't meat always red?
Luke Iles explains meat colour from behind the counter at The Lucky Pig in Bentleigh. Watch on YouTube.
What gives meat its red colour?
Myoglobin is the main pigment responsible for meat's colour. It is a protein in muscle that holds oxygen. That familiar red colour comes mainly from muscle pigment, rather than blood.
Why is vacuum-packed beef purple?
Vacuum packaging removes most of the air around the meat. With little oxygen available, myoglobin takes on a darker, purplish-red appearance. That colour on its own does not mean the beef has gone off.
What does “blooming” mean?
When you open the pack, oxygen reaches the surface and binds to myoglobin, forming oxymyoglobin. This produces the brighter cherry-red colour you recognise at the butcher's counter. The change can begin quite quickly, although the time varies.
What about brown meat?
Brown colour is a different change: myoglobin can oxidise into metmyoglobin. It is not simply another name for the purple colour of low-oxygen meat.
Colour alone cannot tell you whether meat is safe. Follow the use-by date and storage instructions, including directions after opening. Don't eat meat past its use-by date, and don't rely on a normal smell or a red surface as proof of safety.
Got a meat question? Ask our Bentleigh butchers, or browse more answers in Meats Advice.
Further reading: Safe Food Victoria guidance on meat shelf life and labelling and FSANZ guidance on use-by dates.