Meat is mostly water, protein, and fat, with smaller amounts of vitamins and minerals. A lean cut of beef, for example, is about 73% water before cooking. The rest is roughly 20-25% protein, 2-15% fat (depending on the cut), and less than 1% minerals and vitamins. But those broad categories don’t capture the full picture of what’s happening inside a piece of meat at the structural and chemical level.
Water Is the Largest Component
The single biggest ingredient in any piece of raw meat is water. According to the USDA’s Food Safety and Inspection Service, a beef eye of round roast is 73% water before cooking and still 65% water afterward. A whole chicken is 66% water raw and 60% cooked. Even a fattier ground beef (73% lean) is 56% water in its raw state.
Leaner cuts contain more water than fattier ones because water is bound within protein, not fat. So a lean eye of round carries more moisture per gram than a well-marbled brisket. This is also why leaner cuts tend to dry out faster during cooking: there’s more water to lose, and less fat to compensate.
Protein: The Structural Core
The protein in meat comes from skeletal muscle fibers, which are built from long, bundled strands called myofibrils. These myofibrils are made of two main proteins: actin (thin filaments) and myosin (thick filaments). In a living animal, actin and myosin slide past each other to make muscles contract. Their alternating arrangement gives raw meat its visible grain and fibrous texture.
Beyond actin and myosin, meat contains connective tissue proteins like collagen and elastin, which hold muscle fibers together and attach them to bone. Collagen is what makes tougher cuts chewy. It breaks down into gelatin during slow, moist cooking, which is why braised brisket or slow-cooked pork shoulder becomes tender and rich over time while a quick-seared version of the same cut stays tough.
Meat is a complete protein, meaning it supplies all nine essential amino acids your body can’t make on its own: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. This is one reason meat scores high on protein quality scales compared to most plant sources, which typically lack or are low in one or more of these amino acids.
Fat: More Than Marbling
The fat in meat exists in a few different forms. The white streaks you see running through a steak are intramuscular fat, commonly called marbling. Larger deposits sit between muscles or just beneath the skin. At the microscopic level, fat is also embedded within muscle cell membranes as phospholipids, which influence the flavor that develops during cooking.
The fatty acid profile of meat is a mix of saturated and unsaturated fats. Saturated fats, particularly palmitic acid, typically make up around 40-50% of beef fat. The remainder includes monounsaturated fats (oleic acid, the same fat dominant in olive oil) and smaller amounts of polyunsaturated fats, including omega-3 and omega-6 fatty acids. The ratio of these fats shifts depending on the animal’s diet. Grass-fed cattle, for instance, produce meat with higher omega-3 levels compared to grain-fed animals.
What Gives Meat Its Color
Meat gets its red, pink, or pale color from a protein called myoglobin, not from blood. Myoglobin stores oxygen inside muscle cells, and its concentration determines whether meat looks red or white. Beef has the highest myoglobin levels, which is why it’s the deepest red. Lamb and pork contain intermediate amounts, giving them a lighter pink hue. Poultry breast meat has very little myoglobin, making it pale, while darker leg and thigh meat contains more because those muscles work harder and need greater oxygen reserves.
When you cut into fresh beef and it’s bright red on the surface but darker purple inside, that’s myoglobin reacting with oxygen. The exposed surface binds oxygen and turns cherry red. The interior, with no air contact, stays purplish. When meat turns brown in the fridge, the iron in myoglobin has oxidized, a chemical change that affects appearance but doesn’t necessarily mean the meat has spoiled.
Vitamins and Minerals in Small but Potent Amounts
Meat is one of the most concentrated dietary sources of several key micronutrients. Iron content varies significantly by type: 100 grams of beef provides 3.3 mg of iron, while the same amount of chicken breast has just 0.4 mg. Pork sits at 0.7 mg. The iron in meat is in its “heme” form, which the body absorbs two to three times more efficiently than the non-heme iron found in plants.
Zinc follows a similar pattern. Beef leads at 8.2 mg per 100 grams, compared to 2 mg in chicken thigh and just 0.68 mg in chicken breast. Vitamin B12, essential for nerve function and red blood cell production, is found almost exclusively in animal foods. Beef provides about 2.5 micrograms per 100-gram serving, while chicken and turkey offer around 0.6 micrograms. The daily recommended intake for adults is 2.4 micrograms, so a single serving of beef covers your full daily need.
How Muscle Becomes Meat
The meat you buy at a store is chemically different from living muscle tissue. After an animal is slaughtered, its muscles undergo a series of biochemical changes. Without a blood supply delivering oxygen, the muscle cells switch to anaerobic energy production, burning stored glycogen (a form of sugar) and producing lactic acid as a byproduct. This drives the pH of the tissue down from about 7.2 in living muscle to around 5.5 over the following hours.
This drop in pH is what determines the texture, color, and shelf life of the final product. If the pH falls normally and lands near 5.5, the result is firm, bright-colored meat with good moisture retention. If it stalls early and stays high (between 6.0 and 7.2), the meat turns out dark, sticky, and more prone to bacterial growth. If the pH drops too fast or too far (below 5.4), the proteins denature prematurely, producing meat that’s pale, soft, and loses water readily. This is why the same animal can produce very different quality meat depending on how it was handled.
After the pH drops, the muscle stiffens as actin and myosin lock together permanently in a state called rigor. Over the next days to weeks, enzymes naturally present in the muscle slowly break down proteins and connective tissue, which is the process of aging. This is why aged beef is more tender and flavorful than freshly processed meat.
How Cooking Changes the Composition
Heat transforms every major component of meat. Proteins begin denaturing around 40°C (104°F), causing muscle fibers to tighten and squeeze out water. This is why meat shrinks and firms up as it cooks. Collagen starts converting to gelatin around 70°C (160°F), which is the tipping point where tough connective tissue turns soft.
Fat renders (melts out of its solid structure) at temperatures that vary by type, with beef fat melting at a higher temperature than pork or chicken fat. As fat renders, it bastes the surrounding meat and carries fat-soluble flavor compounds. The browning on the surface of seared meat comes from the Maillard reaction, a chemical process between amino acids and sugars that generates hundreds of new flavor and aroma compounds. This reaction happens most effectively above 150°C (300°F), which is why a pale, steamed piece of meat tastes fundamentally different from one with a seared crust.
Water loss during cooking is substantial. A beef brisket goes from 71% water raw to 56% cooked. That lost moisture accounts for much of the weight reduction you see when cooking meat, and it’s the main reason resting meat after cooking matters: it gives the redistributing moisture a chance to settle back into the fibers rather than pouring out when you slice.