What Causes Beef Rainbows?


The USDA says "iridescent beef" is perfectly okay.

Tim Dustrude/Friday Harbor, WA

People are like moths to the flames that are rainbows. The next time there's a rainbow outside, notice how many people drop everything, even important things, to Instagram it. It would be a perfect time for aliens to take over Earth. Rainbows where rainbows shouldn't be, however, cause alarm. Take beef, for example.

How many times have you (if you eat beef) foregone a package of sliced roast beef for a different package because said beef was slightly iridescent? If you don't eat beef, perhaps you've seen a package of said rainbow meat and it reminded you why you no longer eat it. The Internets are clogged with threads like, "Why does deli roast beef look like a rainbow?," and the ever gravid concern, "Subway shiny roast beef?" And while everyone should be spared urbandictionary.com's definition of what a "Beef Rainbow" is, the truth of the matter is, there's nothing inherently wrong with rainbow meat.

In a way, it's sad that meat rainbows are given a bad rap, especially since diffraction gratings in nature are relatively rare.

Beef rainbows aren't a sign of spoiled, tainted, or (sorry) magical beef. There's enough speculation over the integrity of rainbow beef that the USDA's website has a section on "Iridescent Color of Roast Beef" near similar topics like "What does 'natural?' mean" and "what is beef?" According to the USDA, "When light hits a slice of meat, it splits into colors like a rainbow." This is something called a "diffraction grating," essentially what happens when light waves bend or spread around a surface and create a pattern. It's the same thing that happens to make rainbows on the surface of a DVD. It's understandable that folks mistake diffracted light as a sign of spoilage, especially since the main color created by meat diffraction gratings is green. There is a reason why in Dr. Seuss's Green Eggs and Ham, the central conflict of the protagonist is his strong apprehension against eating green meat.

Speaking of ham, beef is not the only meat known to have rainbows. However, when cooked beef is sharply sliced against the grain of the muscle fiber, this, coupled with the moisture in the beef, creates an excellent surface for producing rainbows. "In my opinion," Dr. Thomas Powell, Executive Director of the American Meat Science Association, told me, "The reason it shows up in roast beef is because the cuts of meat that are used in most roast beef are more prone to iridescence, particularly in the round," hence the reason why the USDA singles out roast beef as being especially colorful.

In a way, it's sad that meat rainbows are given a bad rap, especially since diffraction gratings in nature are relatively rare -- and I say this as someone who doesn't eat red meat. Sure, one can see the the vibrant iridescence of peacock feathers or the milky rainbows of an abalone shell and marvel at the rich tapestry that is nature. But it is under the flourescent light of our grocer's deli section where we can look at a rainbow on a slice of beef and know the natural diffraction grating responsible for it is shared with very few things, including the antennae of seed shrimp, and the shells of animals that haven't lived for hundreds of millions of years. A rainbow worth Instagramming as much as any other, for sure.

Jump to comments
Presented by

Taylor Orci is a journalist and comedian based in Los Angeles. She has contributed to NPR, SlateNew York Magazine, the Independent Film Channel, and Adult Swim.

Get Today's Top Stories in Your Inbox (preview)

When Will Robots Take Over the World?

"In a sense, we're already becoming cyborgs."

Elsewhere on the web

Join the Discussion

After you comment, click Post. If you’re not already logged in you will be asked to log in or register. blog comments powered by Disqus


Is Wine Healthy?

James Hamblin prepares to impress his date with knowledge about the health benefits of wine.


The World's Largest Balloon Festival

Nine days, more than 700 balloons, and a whole lot of hot air


The Origins of Bungee Jumping

"We had this old potato sack and I filled it up with rocks and dropped it over the side. It just hit the water, split, dropping all the stones. And that was our test."


Is Trading Stocks for Suckers?

If you think you’re smarter than the stock market, you’re probably either cheating or wrong


I Spent Half My Life Making a Video Game

How a childhood hobby became a labor of love



More in Health

Just In