Why does beef change colour?
by FarmClub Editorial
Why Does Beef Change Colour? The Answer May Surprise You!
Sometimes, when buying beef, you may notice a difference in colour between the meats in the refrigerators. One pack of beef is bright red, and the other might be darker, while another meat placed far away may appear green or grayish.
You may have asked yourself this question before.
"Why are the same beef parts sometimes dark purple and occasionally bright red? Is the dark beef stale? Does purple mean "dirty blood"?"
While these sound like simple questions, many people need clarification on the meat colour changes.
So to understand why your steak changes colour when refrigerated, you need to know how beef changes colour.
What causes beef to change colour? Let's look at why all this happens and what you can do to prevent it!
Why Does Beef Change Color?
You might be surprised to learn that blood colour does not determine the colour of beef meat. The capillaries between the muscles transport blood, but if you look closely, the beef fibres are also red.
Research states that a protein found in muscle tissues called Myoglobin is primarily responsible for the meat colour of all warm-blooded animals. 
The "Myoglobin" contained in the muscle itself is dark purple. After the meat is cut, the iron in the Myoglobin comes into contact with the air. It is converted into Oxymyoglobin, thus giving the meat a bright cherry red colour.
So this means that the purple-red meat is not stale; it is fresher than bright red!
Does Beef Change Color When Frozen?
As long as you look at the vacuum-sealed steaks in the supermarket freezer, you will find that most of them are purplish red because they have not yet oxidized.
Try this the next time you cook at home. When you cut through a large piece of raw beef, the meat will start dull in colour and turn bright red over time.
Oxidized Steak Vs Spoiled
In addition to oxidation, Myoglobin has a form: denatured Myoglobin (Metmyoglobin). 
When the beef is left for a period of time, the enzymes in the meat will convert Myoglobin into gray-brown denatured Myoglobin, making the meat look dirty and making people think it has been spoiled. Still, if there is no smell, the touch will not be too sticky, and the brown meat is no problem to eat.
In addition to being left for too long, meat "deficient in oxygen" will turn gray-brown.
Have you ever encountered a large package of ground beef or beef slices repurchased from the store? Although the surface is bright red, after peeling it off, you find the bottom is gray-brown. The reason is that the Myoglobin on the surface turns bright red after oxidation. Still, the meat at the bottom cannot come into contact with the air, resulting in hypoxia and the formation of denatured Myoglobin, which turns taupe, which makes the meat in the same package produce multiple colours.
In short, depending on the chemical state of the iron and its exposure to oxygen, Myoglobin has three natural colours.
- When no oxygen is present, the meat appears purple-red, similar to vacuum-packed beef, and is in the deoxymyoglobin state.
- When exposed to air, the meat turns a bright red, which is typical of beef in retail displays. The bright red colour indicates the presence of Oxymyoglobin.
- When only trace amounts of oxygen are present, such as when two bright red pieces of meat are stacked on top of each other, the meat appears tan or brown.
Other Factors That Affect Beef Color Change
Several other factors contribute to the change in the colour of beef, including:
- Animal's age at slaughter
- Level of physical activity.
Remember, meat from older animals will be darker due to increased myoglobin levels in the meat over the years.
The flesh of an animal that has experienced a lot of physical activity will have a more significant amount of blood vessels in the muscle and, as a result, will also have a more substantial amount of hemoglobin, and its colour will be a more robust red.
Does Beef Change Color When Frozen?
The simple answer is yes.
It is true that another factor that affects the color of beef meat is the way it is stored in the store and in your home refrigerator. However, if the meat has been stored at an average refrigerator temperature for a short time, minor colour changes are not harmful to health.
Pay attention! Many sales outlets have display areas illuminated with special lighting that causes the meat to change colour in the freezer. To avoid an unpleasant surprise at home, always examine its colour and texture in the general lighting of the space.
When Beef Changes Color, Is It Bad?
The general answer to this question is "Not always." Colour changes are a physiological phenomenon in fresh and frozen meat that does not constitute unequivocal evidence of spoiled meat.
When the meat spoils, in addition to the colour changes, there are also other factors like;
- There will be odour changes. Fresh meat has the characteristic typical smell of fresh beef. Spoiled meat has a rancid smell.
- A sticky layer will form on the product's surface, indicating that the meat has spoiled and should not be consumed.
- The depression of fresh meat after finger pressing can be restored immediately. Whereas the depression after finger pressing of spoiled beef cannot be restored, visible marks remain.
When beef is fresh and protected from external factors such as air, oxygen, temperature, and so on (for example, by vacuum packaging), Myoglobin and hemoglobin play a significant role in determining its colour (as already explained before). Beef exposed to air and room temperature for an extended period but has not changed colour can be considered "cured meat," as various substances preserve the colour. In most cases, it is recommended that such meat products be avoided and that natural meat with as few artificial additives as possible is consumed.
Don't jeopardize your health. Purchase beef from stores or markets that have quality control.
 Vanek, T., & Kohli, A. (2019). Biochemistry, Myoglobin.
 Boles, J. A., & Pegg, R. (2010). Meat color. Montana State University and Saskatchewan Food Product Innovation, Program University of Saskatchewan.