Iridescence in Deli Meats

Posted by Christopher R. Raines :: Have you ever seen roast beef or another deli meat that has a “mother-of-pearl” or “greenish” appearance?  I have.  Many times.  This develops not because the meat has spoiled, but because of the way light is reflected. Yes, light reflection.  The meat is still perfectly fine! In short, the multicolored shimmer results from the angle at which light is reflected — depending on the angle at which the muscle fiber is cut and relative “wetness” of the product, light may (or may not) be reflected differently.  I was reminded of this phenomenon when this article about “Mystery of the Green Sheen on Subway Roast Beef Solved” (below).  The sharper the meat slicer, the more likely iridescent deli meat is.


It has been years since my Subway sandwich artist days, but I think I could still make a delicious sub if put behind the counter. I worked there for over three years, during which time I noticed a few odd things. 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.

When reading a story in the Sun Chronicle Online about a Massachusetts Subway’s green roast beef, the memories came back to me and I decided to do some investigating.

A co-worker who worked in a meat laboratory explained to me, and this University of Saskatchewan paper on meat colour agrees, that the odd colour I was seeing was likely due to light reflections on sliced meat muscle fibers (which is not a food safety issue).

From the paper,

Iridescence is a common problem in sliced roast beef and ham products. The dominant color is frequently green and consumers sometimes confuse this with green myoglobin pigments associated with microbial growth. The iridescence of meat products is produced by a combination of the angle of incidence of the light on the muscle fibres and the wetness of the surface. 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.