It’s kind of unavoidable: if you cut into a big juicy, rare steak you’re gonna get
some juice.
Watery red liquid seeps out of the meat and onto the plate, and… it kind of looks like
blood.
But I have good news for people who like to eat red meat but don’t like to eat blood:
it’s not blood, it’s just water, plus a handy protein called myoglobin.
All meat is muscle, but the muscle looks different depending on what it’s used for.
White meats, like turkey and chicken, come from muscles that are used in short spurts
every so often, but have to get moving quickly. Think of a chicken breast: they don’t actually
use their wings very often.
Red meats -- like beef, lamb, and even pork -- come from muscles used for long, strenuous
activities, like carrying a huge cow around all the time. Before cooking, these meats
are a pinky reddish color.
Holding up a heavy cow is some serious work! Work that requires a lot of oxygen for fuel.
Which is where myoglobin comes in.
Myoglobin is a special protein with an iron atom at its center, which bonds with, then
stores and delivers oxygen to muscle cells.
It works together with hemoglobin, another oxygen-carrier, to get oxygen to the cells
that need it.
The difference between red and white meat comes from the levels of myoglobin in the
muscle.
The myoglobin protein itself is red, so the more myoglobin in the cells, the redder the
meat appears.
And the juice that’s spilling out of your meat? That’s a combination of water and
myoglobin. The animal’s blood was removed when the meat was processed.
Beef is around 0.8% myoglobin, and lamb has a little less, at 0.6%.
And all of those ads have been lying to you, because at 0.2% myoglobin, pork is generally
considered red meat, too. Chicken only has about a quarter of that amount.
But what about humans?
Well, our flesh is about as red as red meat can get, at 2% myoglobin.
If you happen to like steak, but don’t want red juice, you have options.
Myoglobin is red when it’s bonded with oxygen. When meat is cooked rare, up to about 60 degrees
Celsius, the color stays.
Above that temperature, the iron atom in myoglobin loses an electron, and therefore its ability
to bind with oxygen.
Instead, the myoglobin forms a new molecule called hemichrome that gives medium and well
done meat its brown-gray color.
Myoglobin will also turn brown if it’s exposed to air for long enough, because that makes
the iron atoms lose an electron too.
So checking the color could be a handy way to tell if your store-bought meat is fresh.
It doesn’t always work, though, because some meat producers add compounds that keep
the meat red, and the color can last way past the expiration date.
But if you do end up buying that red meat and cooking it rare: I hope you enjoy your
oxygen-rich protein-water.
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