Can you tell if meat is safe by looking?

Meat pigments (L to R): myoglobin, oxymyoglobin, metmyoglobin.

While handling food safely using the 4 basic steps of cook, clean, chill and separate is important, we encourage consumers to also use their senses to guide decision-making.  Does the product look and smell OK? Often a bright, attractive color leads a consumer to choose a particular package of beef from the grocery store. So, why are there differences in the color of beef or ‘red meats’ and what do they mean?

Factors that affect the color of meat. Myoglobin, a protein, is responsible for the majority of the red color. Myoglobin doesn’t circulate in the blood but is fixed in the tissue cells and is purplish in color. When it is mixed with oxygen, it becomes oxymyoglobin and produces a bright red color. Color is also influenced by the age of the animal, the species, sex, diet, and even the exercise it gets. The meat from older animals will be darker in color because the myoglobin level increases with age. Exercised muscles are always darker in color, which means the same animal can have variations of color in its muscles.

Meat color can change depending on how it’s packaged and how long it’s stored. Freshly sliced beef is a purplish color due to the myoglobin. But as soon as myoglobin is exposed to the air, it reacts with oxygen to form bright cherry-red oxymyoglobin, the color we associate with fresh meat. Meat that is vacuum packaged, where the oxygen is excluded, will retain its purplish color. In most retail cases you’ll find beef wrapped in plastic wrap that allows oxygen to pass through, this helps grocery store meats retain the cherry-red color that consumers have come to expect. After a time, however, continued exposure to oxygen leads to the formation of metmyoglobin a pigment that turns beef brownish-red. The color change does not mean the meat is spoiled; it does suggest that the meat may not be as fresh. When safely stored in the refrigerator or freezer, color changes are normal for fresh meats.

Does color change indicate spoilage? Color changes are normal for fresh product; you’ll notice color change as you store fresh meat in the refrigerator and even in the freezer. The freshest beef is purplish in color, with the color changing to cherry-red and then to brown-red over time. You may even have noticed ground beef that is cherry-red on the outside (oxymyoglobin) and either purple (myoglobin) or brown-red (metmyoglobin) on the inside – two colors at once! These differences in color do not mean that the meat is spoiled. With spoilage there can be a change in color—often a fading or darkening – but more importantly with spoilage beef tends to develop an off-odor, to be sticky or tacky to the touch, or it may be slimy. If beef has developed these spoilage characteristics, it should not be used.

What about the white dried patches that develop on frozen meat? The white dried patches indicate freezer burn. When meat or poultry has been frozen for an extended period of time, or has not been wrapped and sealed in freezer-appropriate packaging, freezer burn will develop over time. Freezer burn is an area where the muscle tissue has dried out. The product remains safe to eat, but the areas with freezer burn will be dried out and tasteless; for best quality trim areas of freezer burn away before cooking and eating.

The USDA has developed a fact sheet on The Color of Meat and Poultry (English) En Español PDF And, as always, stay food safe. Barb