This week's experiment came to me while I was
preparing a roast.  To try it, you will need:

a piece of beef, such as a roast, some stew meat, etc.
a knife

First, look at the piece of meat.  It should have a
nice, red color.  Now cut the meat, and look at the
inside.  Instead of being red, it is probably a
darker, reddish brown.  What is wrong?  Is this a
piece of old meat?  Did the butcher dip it or spray it
with something to make it look fresher than it is?
Let's find out.  

Put the piece of meat that you cut onto a plate or
saucer and then put it into the refrigerator.  Do not
leave it on the counter, or your cat will have it for
a snack.  (Voice of experience talking.)  After about
15 minutes, look at it again.

The part that was dark has now turned bright red, just
like the rest of the outside.  Cut the meat again, and
again you will find that the inside is a dark, reddish
brown color.  OK, so what is happening?

Many people think that the red color of fresh meat
comes from blood.  Actually, the red color comes from
a substance called myoglobin.  Myoglobin is related to
hemoglobin, the part of your blood that carries
oxygen.  Myoglobin also holds oxygen, but it holds
that oxygen inside the muscle, keeping it ready for
when the muscle needs it for rapid movement.  Your
muscles use oxygen when they move, and if they run out
of oxygen, then your muscle starts to hurt from
overuse.  

When the cow was killed, its heart stopped pumping
blood to the muscles.  The oxygen in the myoglobin was
used up, and it turned a dark color.  When you cut the
meat, the myoglobin was exposed to air, allowing it to
absorb oxygen from the air and turn the bright red
color.  Myoglobin is also changed by heat, which is
why the meat changes to brown when you cook it.  

Not all meat contains myoglobin.  For example, the
white meat of a chicken breast is fast contracting
muscle, which uses glycogen instead.  Those muscles
are for sudden motion, such as bursting into flight
when a predator threatens.  Without the myoglobin, the
meat is white.  The muscles of a chicken leg are slow
contracting muscle, which does use myoglobin, so you
get dark meat.  Muscles that are used a lot, for
walking or running need the myoglobin for endurance.
That is why ducks have all dark meat, since they fly
long distances.  

Right, I'm gonna beleive something I read on the internet...