Have you ever wondered why that rich red-looking steak you bought a day or two ago has now turned grey in your fridge? For those who eat meat, you may think the color of the product is a surefire way of assessing its freshness and its quality – the redder the better, right? Well, color is not always a trustworthy indicator, as supermarkets have tricks to superficially enhance its color. So is grey streak automatically bad for you?
Where does the red in “red meat” come from?
Red meat, sometimes known as “dark meat”, gets its color from myoglobin, a protein that binds to oxygen in muscle cells.
On its own, myoglobin has a purplish-brown color, so freshly butchered meat can look a duller color. But when myoglobin is exposed to oxygen, it forms the compound oxymyoglobin which is lighter and turns the meat into the richer, redder color we would associate with a healthy product – though that is simply an “association”.
So contrary to what you may believe, when you order a rare steak to the table, the red fluid on your plate is not blood but water and myoglobin.
Over time, the presence of oxygen eventually turns the meat to a greyish-brown color. This is due to the continued oxidation of the myoglobin, which becomes metmyoglobin. The New South Wales Food Authority explains that a larger surface area means minced meat is more likely to turn gray than whole cuts. Despite what you may think, this alone does not mean the meat is inedible or spoilt (though you should still be cautious).
If your refrigerated steak has just turned grey, this may be a result of oxygen in the fridge, rather than a sign of it starting to rot. However, as this process usually takes a few days to occur, it is still worth checking the meat before you cook it (especially if it smells and/or is slimy), as the USDA states that it may be a sign of meat starting to spoil if all of it is gray or brown.
When you buy steak from a store, you may find it is purplish and darker while in the wrappings. This is because the meat needs oxygen to turn red and the vacuum-sealed package prevents this oxidation from occurring.
This may make you wonder why some store-bought meat is still richly red even though it is sealed in plastic. This is usually because supermarkets often use specially designed plastic that is slightly porous. Although the holes in the plastic are too small to let fluids escape, they nevertheless allow air to get in and out.
Source Link: Why Does Fresh Steak Turn Gray And Is It Safe To Eat?