Meat is primarily composed of muscle tissue, the part of an animal’s body responsible for movement. This tissue undergoes biological transformations after an animal is slaughtered, converting it into the product we recognize as meat. While muscle tissue forms the bulk, meat also contains other components that influence its texture, flavor, and nutritional value.
What Muscle Tissue Is
Muscle tissue is made of specialized cells known as muscle fibers. These elongated cells contain protein filaments, primarily actin and myosin, which slide past one another to produce contractions. This interaction is powered by adenosine triphosphate (ATP), the energy currency of cells, allowing muscles to relax and contract.
Muscle fibers are organized into bundles, surrounded by layers of connective tissue. The sarcoplasm is filled with myofibrils, which are long chains of contractile units called sarcomeres.
How Muscle Becomes Meat
The transformation of muscle to meat begins immediately after an animal is slaughtered, when muscles stop receiving oxygen and ATP production ceases. Initially, muscles remain pliable in a “delay phase” as residual ATP is still present. As ATP levels deplete, muscle fibers become stiff due to the permanent formation of cross-bridges between actin and myosin filaments, a process known as rigor mortis, or “stiffness of death.”
During rigor mortis, the muscle’s pH declines due to the accumulation of lactic acid, a byproduct of anaerobic metabolism. This decrease in pH can affect the rate at which rigor mortis sets in. Following rigor mortis, natural enzymes within the meat begin to break down proteins, which helps tenderize the meat over time. This tenderization, often referred to as aging or conditioning, improves the meat’s texture and can enhance its flavor.
Other Components of Meat
While muscle tissue is the predominant component, meat also includes other structures that contribute to its characteristics. Water makes up a large portion, around 75% of raw meat, which is why meat loses weight during cooking. Proteins account for approximately 20% of meat’s composition.
Fat is another substantial component, present both between muscle fibers (intramuscular fat, or marbling) and as external layers. This fat contributes to the flavor, juiciness, and tenderness of cooked meat. Connective tissue, such as collagen, also plays a role. Collagen, found in and around muscle fibers and in tendons, can become soft and soluble, forming gelatin when cooked with moisture, which tenderizes tougher cuts.
Elastin, found in ligaments, is more resistant to cooking and remains tough. Meat also contains smaller amounts of carbohydrates, minerals like iron and phosphorus, vitamins (especially B vitamins), and pigments such as myoglobin, which gives red meat its color.