Grass fed beef, sirloin steak, discoloured?
I have some NY sirloin strip steaks with a layer of fat on the top. Some of the fat in this layer is yellowish. Also, on one of the steaks, this layer has a small patch of bluish/purplish type of color like a dye spilled on it.
Is it safe to eat?
If the blue/purple mark is on the outer surface of the fat it most likely came from the USDA inspection stamp. By law all beef must be inspected by the USDA. They stamp an instpection mark (many of them in fact) on the surface (fat layer) of the carcass if it passes. This stamp is a food safe dye which is blue/purple in color. I believe it is made from grape juice.
I've encountered those colors in beef before. Doesn't fat naturally have a yellowish tinge to it? And I don't think the bluish/purplish color is dye.
"All warm-blooded animals contain a pigment called myoglobin in meat tissues. This pigment is normally a dark grayish-purple but when it comes in contact with oxygen, it becomes oxymyoglobin and reacts by turning a deep red color. Meats that are vacuum-packed have not been exposed to oxygen long enough to turn red.
It is for that eye-pleasing coloration that most fresh ground beef sold in clear packages at the market is packaged using a clear film that is oxygen permeable. The oxygen goes through the film and allows the meat to turn that pretty red color we associate with fresh beef. This is why it is not recommended to freeze meat in store packaging."