Animal muscle turns to meat after slaughtering. Meat is surrounded by a layer of connective tissues, consisting almost entirely protein collagen. Meat tissues are composed of three main factors, water, protein (connective tissue) and fat. Carbohydrate also appears in meat as it gives the browning effect of meat when cooked. Without this carbohydrate, the desirable flavor and appearance of browned meat would not be achieved.

Meat are mainly referred as red or dark and white meat. Red or dark meat is mainly made up of muscles with fibers that are called slow fibers. These muscles are used for extended periods of activity, such as standing or walking and need a consistent energy source. The protein myoglobin stores oxygen in muscle cells, which use oxygen to extract the energy needed for constant activity. Myoglobin is a richly pigmented protein. The more myoglobin there is in the cells, the redder or darker, the meat is. Red meat is red because the muscle fibers that make up the bulk of the meat contain a high content of myoglobin, which are colored red. Myoglobin, a protein similar to hemoglobin in red blood cells, acts as a store for oxygen within the muscle fibers.

White meat is made up of muscles with fibers that are called fast fibers. Fast fibers muscles are used for quick bursts of activity, such as fleeing from danger. These muscles get energy from glycogen, which is also stored in the muscles. White meat as in fish has a translucent "glassy" quality when it is raw. Animal such as calf and pigs are also categorized as white meat. Veal meat is white because it is slaughtered after the calf been milk fed, approximately up to one year old. Pigs are lazy animal; they are not as active as cows, so their body contains more fat than any other animal. White meat is white because there is less usage in the muscle. Myoglobin content is low in these muscles. This is why chicken breast, pork and veal are slightly pink or white, before or after cooked. Fish is white because it lives in water and does not need to support its own body weight. Basically, there are no myoglobins in these muscles.

The difference between meat and fish muscle tissue is that there is no tough connective tissue between the muscles and bones.

Cows and pigs are both sources of dark meat, though pig is often called "the other white meat." Pigs muscles do contain myoglobin, but the concentration is not as heavy as it is in beef. Chickens have a mixture of both dark and white meat, and fish is mainly white meat. Chicken spend a lot of time walking around and standing. Their thigh and leg muscles are used constantly, so the meat from these parts is slightly darker than its breast. Since they rarely fly, and then only for very short distances, the meat that comes from the breast and wings is white. In contrast, wild birds such as ducks fly a lot; the meat from their breasts and wings is dark. Same goes with their legs, as they use them for swimming.

Cows spend a lot of time standing, walking and so their muscles are constantly being used. Therefore, beef has a fairly high concentration of myoglobin and is dark red. Pigs also can spend quite a bit of time standing and roaming around. The pink color of pork is due to myoglobin, but because the animals used for pork and veal are young and small, their muscles are less developed and do less work. Therefore, pigs and calf have a lower concentration of myoglobin in their muscles than cows. The only similarity between these four animals is that they are mammals on land. Fish float in water and do not need constant muscle energy to support their skeletons. Most fish meat is white, with some red meat around the fins and tail, which is used for swimming. The pink colored of some fish, such as wild salmon and trout, is due to astaxanthin, a naturally occurring pigment in the crustaceans they eat. Fish such as sharks and tuna has a dark or red flesh because it contains more myoglobin as they are fast swimmers and a

migratory fish.

Juiciness and tenderness are two very important factors when it comes to meat quality. Both factors are influenced by the cut of meat and how long the meat is cooked. The more a muscle is used, the stronger and therefore tougher, the cut of meat will be. In contrast, the longer meat is cooked, the more liquid it loses and the tougher it becomes. Factors that also influence tenderness and juiciness are: The animal's age at slaughter, the amount of fat and collagen (connective tissue) contained in particular cuts and to a small degree, brining.

Collagen is a long, stiff protein that is the most prevalent protein in mammals. It's made up of three separate molecules composed of amino acid chains, twisted around each other, something like the way fibers are twisted around each other to form a rope. This structure is what makes the collagen so strong; this strength is also what makes it more difficult to break down. The more collagen there is in a piece of meat, the tougher it is to cut and to chew. Skin is mostly collagen, as are the tendons that connect muscles to bones. For cuts that are high in collagen, cooking with methods that use slow, moist heat, such as stewing or braising, are the best. Collagen is soluble in water and when it is cooked slowly with moist heat, it becomes gelatin.

Collagen can be less tough by slicing up the meat into smaller pieces, which makes the fiber smaller and easier to break apart. Weight-bearing muscles and muscles that are constantly used contain higher amounts of collagen than muscles that aren't used for support or aren't used as frequently. Cows and pigs have higher amounts of collagen in the legs, chest, and rump. Pork is generally more tender than beef, because pigs are usually slaughtered at a younger age than cows and so their muscles are less developed and have less collagen than those of cows.

Fish muscles are quite different from those in mammals. Fish float in water and so don't need muscle to support their weight. Their muscle fiber are very short called myotomes and are held together by connective tissue called myocammata, which is much more delicate than collagen and breaks down much more easily when cooked. The only muscles that most fish use extensively are around the tail and fins (areas that aren't eaten as often by humans), which are used for constant cruising around in the water. Once caught, (dead) fish are stored in an ice room with standing temperature of 1-3'C.