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.
If the fibres are pulled slightly out of alignment during slicing, the light strikes the fibre at an angle scattering light which appears as the rainbow or greenish color on the surface of the meat. Whether or not this explains the green on the Massechusetts Subway’s roast beef, I do not know, but does answer a question I forgot I had.
One way to consider this is that roast beef sitting in your fridge may turn a little gray or green. Because deli meats are cured, their chemical structures are changed. After this happens, they’re more likely to change color after coming into contact with oxygen or light. Just like with any meat, this color change alone does not indicate spoilage.
What is that green stuff on my deli meat?
One thing was the roast beef. There was always some green gasoline-like sheen on the slices of deli meat (see right). Whenever I had to make a sub that had roast beef I’d get nervous and concerned the customer would ask what it was – I had no idea – until today.
This is why you’re much more likely to see this rainbow effect on processed deli meat that’s cooked and/or cured than on raw meat. The former has a firmer, tougher texture and the picket fence structure keeps its shape well when deli meats are sliced.
It’s intuitively obvious that if your slice of “red” meat has turned green, it shouldn’t be eaten. Like many other things that are intuitively obvious — a flat earth springs to mind — it’s also wrong. Iridescent hues can occur even in the freshest of roast beef, so they’re not a good indicator of spoilage.
Why do some deli meats Shimmer and others remain dull?
The color of the meat matters. Dark cooked meat like roast beef and bright cured meat like ham are more likely to show iridescence because the background colors provide a starker contrast to the pearly greens and orangey reds that you’re most likely to see coming off of shiny meats.