Is Iridescent Beef Normal? Yes, And Here's Why

Whether you've seen an iridescent sheen on beef at your local butcher, or have noticed those rainbow spots on deli meat, you may have wondered if it's safe to eat or if the discoloration can cause food poisoning. To get to the bottom of it, we chatted with Dr. Bryan Quoc Le, founder and principal consultant at Mendocino Food Consulting. And according to Dr. Le, it's actually very normal (and safe!).

While it may cause a pause initially, Dr. Le confirmed that the rainbow hue often seen on beef is simply a normal light reaction to the meat being sliced. "This optical effect occurs when the regular spacing of muscle proteins (particularly myofibrils and connective tissue) splits light into spectral colors, similar to a prism," he said. While that all sounds very sophisticated, it just means that the oxidation is a completely normal "physical light interaction" when the beef is cut, and absolutely nothing to be worried about. "Although visually striking, this iridescence is unrelated to spoilage and frequently develops during standard processing," Dr. Le said. Phew!

According to Dr. Le, there are some factors that can contribute to meat iridescence. For example, he said that the cutting angle can significantly influence whether or not the beef gets that sheen. He mentioned that it's most common when a piece of meat is cut at a perpendicular angle. This is because this angle exposes more "regularly aligned [muscle] fiber ends." Meat also contains various pigments that can give a colorful hue when processed, or when light hits it a certain way.

Additionally, storage conditions where meat is exposed to direct light or some oxygen can also enhance the chances of iridescence. To combat this and ensure your meat looks its best, he recommends storing it in a vacuum-sealed package and keeping it away from light. 

While a rainbow hue is safe, there are other colors on sliced deli meat that should be avoided. These include sliced beef that looks gray, brown, or dull. Ground meat, however, can sometimes turn these colors when exposed to oxygen and still be safe. Luckily, there are other ways to test. If the meat's texture has turned slimy or sticky, it should be tossed out. You should also perform a smell test, and if the meat has a foul odor (believe us, you can tell), discard it.