Recently I bought a package of sliced pork from the local grocery store, and had most of it for dinner on the same day. The next day, I noticed that all of the leftover slices had an iridescent green covering the surface! The weirder thing was, on closer inspection, the iridesent green turned orange if I looked from a different angle. Thinking that it was some funky strain of mold, I tossed it.
I finally had a chance to ask my trusted Google today, only to find out that the iridescent colours were probably benign:
"Iridescence in meats, specifically beef, can be detected in some of the muscle tissues of some animals before and after rigor mortis. It is most common in the muscles comprising the round, navel and brisket."
"The type of light and the angle of the light reflecting off the muscle will have an effect on the visual brightness of the various iridescent colors. The most common color is an iridescent green, with the next most common color an iridescent orange-red."
The article did not seem to point out the exact mechanism that caused the psychedelic appearance. Can anyone fill in on what might be going on? Was it really benign? And just wondering if this happens much?
Thinking back, it was pretty cool and I wish I had taken a picture of it.
It is totally benign, it can occur on the freshest meat, immediately after slicing. Typically, the sharper the slicing blade, the more startling the effect. Also, the closer the cut to the precise end grain of the meat, the brighter the reflected colors. You'll rarely if ever see this on an emulsified product such as bologna, it's most common on beef, and to a lesser extent, ham.
I once wrote a lengthy paper on this very subject, but alas....it was before the time of computers. I feel old.
If the muscle fibers are of the correct size and spacing, about the order of the wavelength of visible light or a multiple,and the spacing is regular, then the repeating pattern can act as a diffreaction grating, reflecting white light into one or more spectral colors. The surface cannot be smooth, as it would be if wet, but the partial drying of the surface allowed the repeating pattern of the muscle fibrils to reflect light as a diffraction grating. Mystery solved.
From the USDA Food Safety and Inspection Service:
What causes iridescent colors on meats?
Meat contains iron, fat, and other compounds. When light hits a slice of meat, it splits into colors like a rainbow. There are various pigments in meat compounds that can give it an iridescent or greenish cast when exposed to heat and processing. Wrapping the meat in airtight packages and storing it away from light will help prevent this situation. Iridescence does not represent decreased quality or safety of the meat.