It has been brought to my attention by some customers I know shopping at the same supermarket I do that some of the meat in the meat case has a shiny, iridescent appearance. They pointed out to me a package of fresh cut eye of round steaks that were on display and had a greenish/yellowish cast to part of the steak. Almost "rainbow" like. See the beef eye of round picture above as an example.
This greenish cast was a little shiny but as I would turn the package at different angles the greenish/yellowish cast would change shades of green. Again, rainbow like. Iridescent was the way we three decided was the best way to describe this.
The two customers asked, "Is it spoiled?" It's not brown or black -- but iridescent. It's not a moldy green color, but a shiny green tint that changes as you look at it from different angles when I turned the package.
No, I told these young ladies, it is not spoiled. It is the way the light that hits the meat fibers and is reflected off the meat and splits into various colors. Many of us have seen this but we did not know what it was and we assumed that there is something wrong with the meat.
When light hits the meat fibers it splits into colors that resemble a rainbow. A good comparison would be if you look at a DVD with light shining on it. As you move the DVD to different angles you will notice that the DVD changes color. Almost "rainbow" like. This is called "diffraction grating" . That is as scientific as we need to get for now.
We had to move the eye of round steak around several times to get the picture you see above. And the flash from the camera also helped show more of the diffracting. In other words, it was not something that just jumped out at us. Knowing that, you may have bought some of this beef in the past and consumed it without even realizing it was iridescent.
The cells and fibers that that make up this muscle have formed in such a way during the time that the animal was growing that they cause the light to diffract, thus forming the "rainbow".
This iridescence is not in all meats, however, I have seen it most often in the beef eye of round steak or roast that these two young ladies were looking at. It is also visible from time to time in the beef brisket and I have seen it in a beef chuck roast. And sometimes you might notice it in a whole muscle ham or even a cooked beef roast that you might purchase from your favorite deli. On a rare occasion, I have noticed it in a leg of lamb. Have you noticed that most of the cuts I have mentioned are from the hind leg? I, along with many other even more scientific people than myself, can not explain this but maybe it has something to do with the fact that the hind legs are used quite a bit so those muscles, because of the work they do to propel the animal forward have a tendency to have muscle fibers gather in such a way.
Trying to keep it simple, I am not going to dive any deeper into the scientific aspect of this. Let's just realize that this iridescent meat is safe to eat. Again, it is just the way the light reflects off of the muscle fibers. Now I'm not saying that any piece of meat that has a tint on green is safe, but don't be alarmed if you are looking at a package of meat and it seems have a small section of the surface area iridescent. If you have any questions at all concerning the safety of the package you are looking at then don't purchase it.
I hope this helps you feel more knowledgeable when purchasing meat from you favorite meat shop. After I explained this to these two customers, they were satisfied that the package of eye of round steaks they were questioning were indeed safe to purchase.