Food Science Question

187
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Joined Sep 27, 2003
Can anyone explain to be why roast beef for instance has a greenish/purpleish/blueish tint on some of the slices at times?

I have had several Marines (I chef for the messhall) ask about it and they’re impression is it’s rancid. Of course, it isnt but I have no idea how to explain what it is or where it comes from..

Can anyone shed some light? 

Frizbee
 
1,447
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Joined Apr 3, 2008
from what I have read it has to do with with light refraction on the beef cells after cooking. Before cooking your eye just sees the red from hemoglobin in the cells of the meat, after cooking the hemoglobin has changed enough to cause light refraction to appear in the green and blue spectrum of light. where before all you could see was red.  Roast beef will feel slimy when it starts to go bad. You'll notice the slime texture on the meat before it even starts to smell bad.
 
32
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Joined Dec 16, 2010
location of the roast, relation to blood vessels, pre-slaughter bruising.  could be a variety of things...most from before you ever got the product to begin with.
 
595
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Joined Jun 28, 2010
Each color of light has a different wave length, depending on how it is reflected, it can be reinforced or canceled.

That's why oil slick on water appears to be rainbow colored, because the thickness of the oil is different. That's how they make lenses to have less internal glare by coating with selective thickness of materials.

On you roast beef, the thin coat of moisture and oil can change the color of the reflected light.

dcarch
 
928
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Joined Mar 16, 2005
seen a similar effect while portioning cold short ribs... there's this oil-slick like rainbow sheen on the surface of the exposed area.
 
5,516
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Joined Apr 3, 2010
This is called a 'rainbow' and it is most common on processed cold cut type meats and smoked meats. From what I am told it has to do with the heat  movement and formation in relationship to oil content of products. in the cooking process. It does not effect taste or quality of product, but sure looks strange.
 
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