Meat comes in a variety of colors depending on the animal it comes from and how it was processed. The natural color of meat depends on the amount of myoglobin in the muscles. Myoglobin is a protein that stores oxygen in muscle cells and is what gives meat its red color. The concentration of myoglobin determines the intensity of the red color. Meat can also take on other colors depending on other factors.
What Makes Meat Red?
As mentioned above, the red color in meat is due to the presence of myoglobin. Myoglobin is found in muscle cells and acts as an oxygen storage unit. The more myoglobin a muscle contains, the darker the red color of the meat. Meat from animals that are more active and use their muscles more will have higher levels of myoglobin. For example, dark meat in chicken and turkey legs has more myoglobin than white breast meat.
When meat is fresh, the myoglobin is oxygenated and bright red. This is referred to as oxymyoglobin. After a few days, the myoglobin loses its oxygen and turns into deoxymyoglobin which has a very dark, almost purplish-red color. This is the color of vacuum sealed packaged meat. Once meat is exposed to air, the myoglobin binds to oxygen again and turns back to the bright red oxymyoglobin color.
White Meat
White meat comes from muscles that are not used as heavily as dark meat and therefore contain less myoglobin. Common examples of white meat are chicken breast, turkey breast, and pork. White meat is lighter in color because the muscles contain less myoglobin and are not as vascularized as dark meat. Cooking white meat to higher temperatures can also denature and coagulate the protein in the tissue, lightening its color.
Chicken and Turkey Breast
Chicken and turkey breast meat is mostly white because the breast muscles are not heavily used and do not require a large oxygen supply. Chicken breast has the lowest natural myoglobin content of all meats. Turkey breast has slightly more myoglobin than chicken breast, but less than dark turkey meat.
Pork
Fresh pork is whitish-pink in color, also due to lower myoglobin levels compared to beef. However, with extended storage times, pork can oxidize and take on a more brownish color. This browning does not necessarily indicate spoilage.
Dark Meat
Dark meat comes from muscles that work harder and require more oxygen. They therefore contain more myoglobin and are darker red in color. Common examples are chicken thighs and legs, turkey legs, and red meat like beef and lamb.
Chicken and Turkey Legs
Chicken and turkey legs come from muscles that are more active and contain more myoglobin. Chicken legs will be reddish-brown to tan in color while turkey legs are often much darker, even purplish-black at the extremities. This very dark color is due to the high myoglobin content.
Red Meat – Beef, Lamb, Goat
All red meat like beef, lamb, and goat are dark red due to their high myoglobin content. These muscles are worked rigorously and require greater oxygen. Grass-fed beef is typically darker in color than grain-fed due to more muscle use. Meat from older, more active animals will also be darker.
Pink Meat
Meat can take on a pink color for a few different reasons:
- Undercooked red meat – When red meats like beef and lamb are cooked rare to medium-rare, the inside remains pink because the myoglobin has not denatured and turned brown yet.
- Fresh pork – Fresh pork can look pink but turns more whitish upon cooking. It should not be eaten rare.
- Processed meats – Meats like ham and bacon are often cured with nitrites or nitrates which give them a characteristic pink color.
- Old meat – Over time, the myoglobin in meat can turn from red to grayish-brown. But when exposed to oxygen, it can turn reddish-pink again. This meat should be discarded.
Grayish-Brown Meat
When meat is cooked well-done, the myoglobin gets denatured by the heat and turns from red to grayish-brown in color. The extent of browning depends on the final internal temperature. For example, chicken cooked to 165°F will be white throughout while steak cooked to 145°F may still be reddish-pink inside. Older meat will also turn more grayish-brown as the myoglobin oxidizes over time.
Cooked Red Meat
When steak, lamb, or other red meat is cooked to well-done, the myoglobin breaks down and the interior color changes from red to grayish-brown. The higher the final internal temperature during cooking, the more denatured the myoglobin will be.
Cooked White Meat
White meat like chicken will turn opaque and whiter as it is cooked to safe temperatures. Turkey and chicken cooked to 165°F are safe to eat but will have a stringy, dry texture. Going past 155°F for chicken or turkey will rapidly dry it out as moisture evaporates.
Old Meat
As meat ages in the refrigerator or freezer, the myoglobin will naturally denature and turn grayish-brown. This is due to oxidation and microbial growth. Meat held for too long will turn unappealing grayish colors and may not be safe to eat.
Green Meat
Meat turning green is not very common. It can happen when:
- Metmyoglobin formation – When myoglobin is exposed to oxygen for too long, it changes to metmyoglobin which has a green color.
- Bacterial growth – Some bacterial spoilage like Pseudomonas can cause a green hue.
- Reaction with gases – Reactions between meat and gases like carbon monoxide or nitrogen dioxide can lead to a green color.
Meat that has turned partially or fully green should be discarded.
Blue Meat
Meat can sometimes take on a blue/purple/gray color due to deoxygenated myoglobin. This is more common in vacuum sealed meat or cured processed meats.
Vacuum Packaged Meat
When meat is vacuum sealed, oxygen is removed from the package and the myoglobin changes to deoxymyoglobin, which has a very dark purplish-red or blue color. This does not indicate spoilage. Once exposed to air, the meat blooms back to a red color.
Cured Meats
Curing meats involves the use of nitrates or nitrites which react with myoglobin to give a characteristic pink color. However, in products like prosciutto or salami that are aged for long periods, the inside can take on a blue/grey color due to the deoxygenated myoglobin.
Yellow Meat
A few instances where meat can turn yellow include:
- Fat oxidation – Fat naturally turns yellow as it oxidizes and becomes rancid.
- Frozen storage – Meat held in the freezer for months may take on a yellowish hue due to oxidation and dehydration.
- Curing – Some curing processes can cause a yellowish color, especially if older nitrate salts are used.
If the meat smells rancid or sour, it should be discarded. Otherwise, the yellow color may just be due to aging but the meat may still be safe to eat.
Black Spots on Meat
Black spots on raw meat are usually due to blood clots or bruises. Small ones can be trimmed off but meat with large portions of black discoloration should be discarded. Black spots on cooked meat can indicate contamination or spoilage.
Blood Clots
During the butchering process, blood can collect and coagulate in the micro-capillaries of the muscle tissue. These small blood clots turn black on the surface of raw meat cuts. They are harmless but can look unappealing.
Bruises
Improper handling of meat can cause bruising of the tissue. Bruises appear as black, blue, or greenish areas on the surface of the meat. Heavily bruised portions should be trimmed off.
Spore-Forming Bacteria
On cooked meats, small black spots can indicate microbial contamination and spoilage. Spore-forming bacteria like Bacillus cereus can survive cooking temperatures and leave black deposits on the surface of meat.
Mold
Mold growth may also look like black spots or areas on cooked meat leftovers. This can occur in refrigerated meats kept for too long in humid conditions.
Brown Spots on Meat
Brown or grayish spots and discoloration on raw or cooked meats can indicate spoilage and oxidation.
Oxidation
When meat is exposed to air, the myoglobin will naturally oxidize and create metmyoglobin, which has a brownish-gray color. This can occur in ground meats or cut meat surfaces over time.
Bacterial Growth
As bacteria start decomposing the meat tissue, it can become slimy and develop brownish mucus-like spots on the surface. Meats with these bacterial growth spots should be discarded.
Freezer Burn
When meat is frozen for too long, the surface can dehydrate and take on brownish-grey dried out areas known as freezer burn. It makes the meat tough and tasteless.
Maintaining Proper Meat Color
To help maintain the appealing red color of fresh meat, it’s important to handle it properly from farm to table:
- Quick chilling after slaughter prevents discoloration in beef carcasses.
- Vacuum packaging or protective atmospheres prevent oxygen exposure.
- Avoid bruising, temperatures fluctuations, and prolonged storage.
- Use fresh meat within 5 days of purchase for optimal quality.
- Cook to proper internal temperatures to denature myoglobin.
Conclusion
The color of meat depends largely on the myoglobin content and oxidation state. Fresh red meat contains oxymyoglobin which gives it the appetizing red color consumers expect. As it ages, it transitions through deoxymyoglobin and metmyoglobin, taking on purple, brown, and eventually gray colors. Freezing, curing, cooking, and bacterial contamination can also impact meat color. While color itself does not indicate safety or quality, drastic changes can signal decomposition and spoilage issues. Understanding the factors that influence meat’s color provides insights into proper handling and storage measures necessary to deliver quality fresh meat.