You know the situation – you’re making a sandwich and grab a few slices of roast beef from the deli. As you lay them on the bread, an odd rainbow-like shimmer catches your eye. Your roast beef is shiny green! Is it safe to eat or has this meat gone bad?
Many of us have encountered this strange optical effect on packaged lunchmeat The good news is these green and purple hues aren’t harmful – in fact, they have a scientific explanation. Read on to learn what causes rainbow roast beef and whether it’s still okay to eat.
It’s Diffraction, Not Spoilage
Relax – that iridescent shine isn’t a sign your roast beef has spoiled. It’s caused by a physical phenomenon called diffraction – the same process that makes CDs shine rainbow colors!
Here’s how it works: muscle tissue contains many parallel protein fibers bundled together like cables. Meat processing aligns these fibers so they’re all oriented the same way.
When light hits this orderly arrangement of fibers, it diffracts and separates into colors like a prism does with sunlight. The resulting rainbow sheen is perfectly natural, not a product of decay.
Fat Content Influences Diffraction
Meat with heavy marbling tends not to shine as much. The fat disrupts the straight parallel fibers diffraction relies on.
This explains why leaner deli meats like roast beef exhibit more rainbows, while fattier cuts like bologna rarely shine.
Cutting Against the Grain Helps
Slicing roast beef against the grain chops those tidy aligned fibers into disarray. This randomness scatters light every which way instead of splitting it into spectra.
So if you don’t like the rainbows, ask the deli for roast beef sliced against the grain. The meat may be slightly less tender, but the optics will be different.
Cooked Meat Diffracts Best
Raw beef rarely shines since its soft fibers don’t yet have the rigid organization to diffract light.
Cooking causes proteins to tighten and form a neater structure. This regularity is key for splitting white light into its color components via diffraction.
So while raw meat can refract a bit, the most vivid rainbows appear on cooked, cured, tightly-structured meats.
Protein Denaturing Enhances Diffraction
Meat processing employs salts, heat, and pressure to denature proteins – causing them to unwind and reconnect in new configurations.
This denaturing smoothes and straightens the meat fibers, creating an even more orderly diffraction grid for light waves to bounce off.
Added Pigments Can Play a Role
In cooked, cured, or smoked meats, naturally occurring pigments can also influence color. Nitrates/nitrites in curing salt can react with meat proteins to form pigments.
Smoking introduces new chemical compounds that also modify color. While diffraction is the main cause of rainbows, added pigments may play a supporting role.
Myth: It’s Mold or Bacteria
Some think meat rainbows mean spoilage – perhaps caused by mold, bacteria, or other microbes. This isn’t the case.
Diffraction’s short-range ordered structure is far different from the disordered fractal patterns that mold and bacteria form. One glance dispels this myth.
Myth: It’s Chemical Additives
There’s also a myth that meat companies secretly treat products to make them shine. But again, diffraction arises naturally from the innate structure of muscle fibers.
As the USDA states, the rainbow sheen is “an indication of the freshness of a meat product rather than any treatment designed to produce it.”
Don’t Worry, It’s Safe to Eat!
The USDA confirms deli meat shines due to physics, not spoilage or chemicals. As long as your roast beef smells fresh and isn’t sticky or slimy, it’s perfectly safe to eat – green tints and all!
In fact, a nice iridescent sheen signals the meat proteins are neatly aligned – a mark of quality processing. Consider it a bonus optical garnish on your sandwich.
So next time your lunchmeat gleams, appreciate the physics at play. Dazzling roast beef makes for an enriching sensory experience! Let us know if you have any other meat rainbow questions.
Why Does Meat Go Rainbow Coloured? | Food Unwrapped
FAQ
What is the green shiny stuff on roast beef?
Can you eat meat that has turned green?
Is iridescent meat safe?
How to tell if roast beef has gone bad?
Why does cooked beef smell like a rainbow?
When light hits a slice of meat, it splits into colors like a rainbow. There are also various pigments in meat compounds which can give it an iridescent or greenish cast when exposed to heat and processing. Iridescent beef isn’t spoiled necessarily. Spoiled cooked beef would probably also be slimy or sticky and have an off-odor.
Why is roast beef so colorful?
“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.
Why is meat iridescent?
Sliced cooked beef or lunchmeat can have an iridescent color. Meat contains iron, fat, and many other compounds. When light hits a slice of meat, it splits into colors like a rainbow. There are also various pigments in meat compounds which can give it an iridescent or greenish cast when exposed to heat and processing.
Why does my roast beef look shaved?
The colorful sheen on a slice of roast beef or pastrami isn’t a sign of spoilage or chemical additives—it’s actually a result of the way the meat is cut. Slicing meat “against the grain” means cutting through, rather than parallel to, the bundles of fibers composing the meat’s musculature.