As requested by Dave (see comments on Two-pronged beef injection), I’ve done a little research about why beef comes in different colours.
It’s down to a water-soluble protein called Myoglobin, which stores oxygen for aerobic metabolism in the muscle. Myoglobin consists of a protein and a non-protein porphryn ring with a central iron atom – which plays a key role in the meat colour.
The factors that determine the meat colour are the oxidation state of the iron and which compounds – oxygen, water or nitric oxide – are attached to the iron portion of the molecule.
As different muscles vary in the level of activity they perform, the amount of oxygen they demand varies. Therefore the concentration of Myoglobin varies in different parts of the cow. Also the levels of Myoglobin increase as animals get older. The more Myglobin, the more intense the colour of the meat will be.
When meat is initially cut it is usually quite dark. Beef is typically a dark purple-red colour. When oxygen from the air comes into contact with the meat, it is absorbed and binds to the iron. As the Myoglobin is oxiginated – turning to oxymyglobin – the beef changes to a bright red colour, which is the colour that most people associate with freshness.
Browning of meat occurs when Myoglobin and/or oxymyoglobin lose an electron, which yields metmyoglobin.
The pigments Myoglobin, oxymyoglobin and metmyoglobin can be changed from one to another, though after cooking the meat, another pigment called metmyoglobin is formed which cannot be changed back.
Vaccum packed meat usually remains a deep purple colour as the oxygen has been removed from the packet and reducing enzymes have converted the meat pigment back to Myoglobin. When meat is taken out of the vacuum pack and exposed to oxygen the colour would begin to turn reddish.
This explains the contrast in colour of the two different types of steak I cooked last Friday. The fillet steaks that were sent from Dubai arrived in vacuum packs. The photo I took was taken only minutes after they were removed from the packet, hence the meat did not have enough time to retain its reddish cololuring.
The Cornish steaks however were exposed to oxygen for a good amount of time and thus the levels of oxymyoglobin were higher, giving the meat a more appealing reddish colour.
Thanks for the question Dave. I hope the above is helpful.
