When I was growing up, my mother always ate roast beef for lunch. It always looked more appealing than my peanut butter and jelly, but I was super weirded out by the iridescent rainbow on the outside of the meat after it had sat in the deli package for a few days in the refrigerator.
Obviously this rainbow was caused by the deli counter worker who was definitely an alien, according to my third-grade mind. I mean, how else are rainbows on meat supposed to form? Well, apparently there's science behind it! Want to be in the cool crowd and find out why?
It's been many years since I thought my local grocery store worker was an alien —although there are a few characters at my local Whole Foods Market that make me wonder. Being 30-some years past that age, I'm ashamed to say that I've only just recently learned what causes this funny phenomenon of the meat rainbow.
It feels like the same type of rainbow you see on top of oil slicks in puddles or on a hologram and there's a reason for it! Thankfully there's no oil, aliens, or puddles involved in the making of my mother's roast beef sandwich, but there is the scientific principle of diffraction.
Essentially, when meat is cut against the grain (as it is in deli meat, as it makes it more tender and yummy), it leaves space between the muscle tissue. This is seen to the human eye as diffraction. White light from the atmosphere hits the negative space and causes the iridescent effect or pattern. This also explains why it happens after the meat has been kept a little longer, as the spaces between the fibers grow larger as the meat fibers dry out slightly.
To think about the number of sandwiches I missed out on is shameful, but now we all know, right? Right! So carry on with your deli counter meats and fear not of alien encounters from your local butcher!