Imagine you are buying steaks for your family. You walk up to the counter at the grocery store to try to decide which package to buy. What do you look for? For many people, one of first things that is taken into consideration is the color of the product. In fact, one of the primary factors for discounting meat products is discoloration. Although the product may be perfectly safe, nutritious and delicious, off-color is off-putting to many consumers. Variation in meat color can be caused by many different factors.
Meat gets its color from the myoglobin that is present in muscle tissue. During life, myoglobin carries oxygen throughout the muscle and is what is responsible for the red color primarily associated with meat. When meat is thawed, myoglobin and water are released creating purge, a liquid often confused with blood. Different muscles have different amounts of myoglobin depending on their use. The more active they are, the more myoglobin present as the muscle requires more oxygen. The level of myoglobin within the muscle can vary based on muscle fiber type and maturity of the animal.
Type 1 muscle fibers are used for long term locomotion (cross country runner) and have higher amounts of myoglobin. Cattle have predominantly type 1 muscle fibers. Beef are locomotive animals and often are consistently walking to reach water and feed sources. The high levels of myoglobin within their muscles create a bright, cherry red colored meat.
Type 2 muscle fibers are used for short bursts of energy (sprinter) and have lesser amounts of myoglobin. Chickens have predominantly type 2 muscle fibers (there are varying degrees of type 2 fibers, but we won’t go into detail on those today). Typically, chickens only need short bursts of energy to make it to their roost or to run for a short period of time. Due to the lower levels of myoglobin, their muscles will have a lighter colored, pinkish tint.
The muscle structure within animals is not strictly one muscle fiber type or another. They can have a combination within they system based on their use (white vs. dark meat). Even breed and production style can cause differences. For example, farm raised turkeys are not required to be very mobile and don’t need sustained locomotion to get food, water, etc. Wild turkeys, on the other hand, will cover a lot more ground and engage their muscles a lot more. They produce a meat that is much darker in color compared to their farm raised counterpart.
In addition to muscle fiber type, maturity can impact final product color. As an animal ages, more myoglobin (what carries oxygen to the muscle and makes it red) is present and gives meat a redder color. This is especially evident in beef animals. Veal, or meat produced from a young calf, will often be a pinkish color. Meat from a traditional market steer is traditionally the bright, cherry red color that we are used to seeing at the retail counter. Meat from old cull cows or bulls, is a darker, deeper, red color that is not as appealing to the consumer.
Additionally, preharvest factors, including diet and stress can impact color. When an animal is harvested, the muscle goes through natural changes to convert to meat. One major change is the pH, or acidity level. Living muscle tissue has a nearly neutral pH of around 7.0. When an animal is harvested, the pH declines, making the meat slightly more acidic (pH of ~5.4). Stress prior to harvest can affect the rate and level of pH decline, causing variation in color. In beef, long term stress can lead to dark cutters (product that is almost purple in color). In pork, stress leads to a product that is pale in color, soft (doesn’t hold shape) and exudative (losing moisture). Keeping the effect of stress on carcass quality in mind is important when handling livestock at home.
In addition to these factors, genetics, sex, harvest methods, oxygen exposure, etc. can all impact product color. Although not all variation in color is a negative thing (muscle fiber type), some may be an indication of a problem in production (preharvest stress). Understanding the production process is important to be able to identify the cause of color variation and determine if it is necessary to implement a change in production.
The Meating Room 