Why meat turns brown

The meat from older animals will be darker in color because the myoglobin level increases with as animals age. Exercised muscles are always darker in color. Because muscles differ greatly in activity, their oxygen demand varies which in turn means the same animal can have variations of color in its muscles.

Also myoglobin levels vary by species which is why beef has more of a red color than pork or lamb. So why does meat turn brown?

Both myoglobin and oxymyoglobin have the ability to lose their oxidation which results in a brown color called metmyoglobin. This essentially means that meat can turn from a bright red color which many associate with fresh to a brown color from a lack of oxygen.

Meat can also turn brown if any sort of contamination that would cause a chemical reaction comes in contact with it. For example, cure sodium nitrite turns raw meat a brownish-grey color think of a cured, uncooked salami if it comes in direct contact with a meat surface, but if that same meat is then heated, the sodium nitrite turns the meat a pinkish color much like ham. In order for meat to maintain that bright red color we are familiar with, oxygen must be available at a sufficient concentration.

That is why grocery stores utilize a small film over their products versus a vacuum package. Browning of meat can also occur with meat that has been chilled for a long period of time about 5 days , ie: taken home from the grocery store and placed in your fridge for some time. Browning of meat can also occur when oxygen partial pressure is low or basically when meat is stacked on top of one another. This is more than likely the case from the photo above. This is also the reason why your ground beef from the store may be red on the outside but brown on the inside.

The changing from red to brown and even the purplish color to red occurs quite easily in meat, the reverse is much difficult. Once meat has browned, it is hard to get it enough oxygen to reverse the process.

Also, this same process is the reason meat does indeed turn brown when you cook it. But once meat is cooked, it denatures the proteins so there is really no going back! All of the protein is not affected at the same time which is why you get different variations of a reddish color at different temperature points. Basically this is what gives us rare, medium rare, medium, well done, etc.

Those colors associated with meat temperatures are basically denatured metmyoglobin! One myth I see commonly brought up is that old meat is dyed red. This is not anything any of us in the meat industry have heard of nor have we found information to supply this so-called practice. The number one indicator of spoiled meat is in fact smell. An off odor will be prevalent to your senses and the most effective way to diagnose spoiled meat.

Another indicator of spoiled meat is tacky or sticky to the touch. Slimy meat not juicy is also a great indicator of spoilage. This especially occurs if meat has been temperature abused. Raw meat that has been heated up not cooked and then re-cooled will often times become sticky or tacky along with possibly a color change. Use these three factors in diagnosing spoiled meat: does it smell, is it sticky, AND does it have color change?

If it is not spoiled, feel free to indulge without worry! If you are like me, you are taking fewer trips to the store right now. Sometimes meat cuts may sit in the fridge longer than you expect them to and they turn brown. So, how do you know if it is safe to eat? But, why did it turn brown? Fresh pork color is really dynamic because the protein in meat is still active and somewhat functional even after the animal has been harvested.

When pork is freshly cut, it is a purplish-pink color because the myoglobin is not interacting with oxygen. After cutting, the oxygen in the air attaches to the myoglobin and the pork turns to the bright pink color that we associate with fresh pork. It would be great if the color would just stay the pretty pink color, but the enzymes in the muscle use the oxygen and take it away from the myoglobin.

As it does that, the really low levels of oxygen in the muscle cause the myoglobin to oxidize and turn brown. This reaction happens at a microscopic level just below the cut surface. A use-by date on a package can also be a good guideline. Some meat may also show an iridescent sheen. This is because meat contains iron, fat, and other compounds. When light shines on a slice of meat, it splits into colors like a rainbow. There are various pigments in meat compounds that can give it an iridescent or greenish cast when exposed to heat and processing.

Wrapping the meat in airtight packages and storing it away from light will help prevent this situation. Hemichrome is the compound that gives medium-cooked red meat its slightly browned color.

While some would call this charred and ruined, others find the crispy carbon-rich exterior divine. Sign up for the best of Food Republic, delivered to your inbox Tuesday and Thursday.

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