We Get Letters v.33: The colors of ground beef

From the inbox comes a question from Bill:

Hi Kate.

Happy Birthday. I turned 40 this year too. Sigh.

I had a question that’s been bugging me lately. If you don’t know the answer, maybe one of your readers does.

You know how ground beef is nice and bright red when you first buy it, then it turns sort of grey after a day in the refridgerator? Or, sometimes you buy it, and when you break it apart, it’s red on the outside, but all grey inside?

What does this mean? Is it a sign that the beef has been sitting around too long? Or does it mean nothing?

I’ve also noticed that if I buy the more expensive ground beef from (for example) Creekstone Farms, it is much brighter red than the supermarket stuff. It *looks* more appetizing, and fresher. But is it, or is that just a trick of some kind?

Best Regards,

bill odonnell

Hi Bill! Thanks for the birthday wishes! After a week or so of being forty, I’ve decided that a person is only as old as they want to be, what with time being an illusion and all.

And yes, the above is simply a rationalization. Ahh, rationalizations- they’re better than sex.

Onto your questions about the color of ground beef. It shouldn’t surprise you that the answer to your question lies somewhere in science, specifically in biochemistry.

Fresh meat color depends upon something called myoglobin. Myoglobin is a water-soluble protein that stores oxygen for aerobic metabolism in the muscle. It consists of a protein portion and a nonprotein porphyrin ring with a central iron atom. It’s this iron atom is that concerns us when we want to discuss meat color.

The defining factors of meat color depends upon the oxidation state of the iron and which compounds are attached to the iron portion of the molecule.

Immediately after cutting into beef, it is quite dark – almost a deep purplish-red. As oxygen from the air comes into contact with the exposed meat surfaces it is absorbed and binds to the iron and the iron starts to oxidize and change colors. The surface of the meat blooms as myoglobin is oxygenated. Myoglobin, in an oxygenated state is called oxymyoglobin, and oxymyglobin has a pigment which gives beef its bright cherry red color. The more myglobin in the meat, the brighter color of red. As a general rule of thumb (meaning that there will be exceptions) the extensive myglobin in meat indicates one or two things.

1) The muscle from which the cut of meat was drawn was an active muscle. Remember that myoglobin stores oxygen for aerobic metabolism in the muscle. An inactive muscle would have less myoglobin. So if you have two three year old cows, and one was stuck in a Concentrated Animal Feeding Operations with no room to run around, and the other had access to pasture and was allow to graze and move about, it would be the latter cow that had more myoglobin.

2) Older cows would have more myoglobin than younger cows. And since CAFO’s don’t have older cows, they would not produce bright red cuts of meat.

So yes, a brighter red would, for the most part, indicate a non-CAFO cow and would likely have been treated better and fed better, resulting in a higher quality cut of meat. Now this is a general rule of thumb, and there may be exceptions.

But how does the meat turn brown? That same oxidation process which changed the myoglobin to oxymyoglobin will eventually cause the Myoglobin and oxymyoglobin to lose an electron which turns the pigment to a brown color and yields metmyoglobin.

So essentially brown meat is indicative of meat that has been exposed to a fair amount of oxygen, enough so that the color dominates the overall composition. In fact, myoglobin, oxymyoglobin and metmyoglobin all exist in some ratio or another. The color of the meat simply indicates which one is currently dominating.

One may ask if the oxidation process can be reversed, or at least slowed down. The answer is yes, and in 2004 some meat producers asked the USDA to permit the gassing of meat with Carbon Monoxide, with the idea that the meat producers would be able to sell the older cuts of meat that once looked brown but no longer do due to the Carbon Monoxide. Consumers generally distrust brown meat, and it wouldn’t sell as well. Luckily for us, many meat producers are discontinuing this practice.

But the thing is, the brown meat wasn’t a sign of bad meat, it was a sign that it had enough time to become oxidized to the point where metmyoglobin dominated the beef. It was less “fresh” than the cuts of meat that had only been exposed to oxygen long enogh to let the oxymyoglobin dominate.

In other words, brown meat is not necessarily bad meat. It’s just not fresh meat. The enemy of meat is not color, but time. The darker the brown, the more time it has been been exposed to oxygen, and the closer it’s getting to it’s “use by” date. Meat the color of a latte is likely edible. Meat the color of chocolate? Yeah, I’d pass on that.

So how do you tell if meat has gone bad? Well, if stored properly, the best indicator is the “sell by” date that should be on the label. If stored improperly, smell is a good indicator as well as any green tint that may be in the beef.

Hope this helps!

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