Woman's Institute Library of Cookery. Volume 3: Soup; Meat; Poultry and Game; Fish and Shell Fish

by Woman's Institute of Domestic Arts and Sciences

STRUCTURE AND COMPOSITION OF MEAT

7. An understanding of the physical structure of meat is essential to its successful cooking. Meat consists of muscular tissue, or lean; varying quantities of visible fat that lie between and within the membranes and tendons; and also particles of fat that are too small to be distinguished except with the aid of a microscope. The general nature of the lean part of meat can be determined by examining a piece of it with merely the unaided eye. On close observation, it will be noted that, especially in the case of meat that has been cooked, innumerable thread-like fibers make up the structure. With a microscope, it can be observed that these visible fibers are made up of still smaller ones, the length of which varies in different parts of the animal. It is to the length of these fibers that the tenderness of meat is due. Short fibers are much easier to chew than long ones; consequently, the pieces containing them are the most tender. These muscle fibers, which are in the form of tiny tubes, are filled with a protein substance. They are held together with a tough, stringy material called connective tissue. As the animal grows older and its muscles are used more, the walls of these tubes or fibers become dense and tough; likewise, the amount of connective tissue increases and becomes tougher. Among the muscle fibers are embedded layers and particles of fat, the quantity of which varies greatly in different animals and depends largely on the age of the animal. For instance, lamb and veal usually have very little fat in the tissues, mutton and beef always contain more, while pork contains a greater amount of fat than the meat of any other domestic animal.

8. The composition of meat depends to a large extent on the breed of the animal, the degree to which it has been fattened, and the particular cut of meat in question. However, the muscle fibers are made up of protein and contain more protein, mineral salts, or ash, and certain substances called extractives, all of which are held in solution by water. The younger the animal, the greater is the proportion of water and the lower the nutritive value of meat. It should be understood, however, that not all of meat is edible material; indeed, a large part of it is made up of gristle, bones, cartilage, nerves, blood vessels, and connective tissue. The amount of these indigestible materials also varies in different animals and different cuts, but the average proportion in a piece of meat is usually considered to be 15 per cent. of the whole. Because of the variation of both the edible and inedible material of meat, a standard composition for this food cannot readily be given. However, an idea of the average composition of the various kinds can be obtained from Fig. 1.

9. PROTEIN IN MEAT.--The value of meat as food is due to the proteins that it contains. Numerous kinds of protein occur in meat, but the chief varieties are myosin and muscle albumin. The myosin, which is the most important protein and occurs in the greatest quantity, hardens after the animal has been killed and the muscles have become cold. The tissues then become tough and hard, a condition known as rigor mortis. As meat in this condition is not desirable, it should be used before rigor mortis sets in, or else it should be put aside until this condition of toughness disappears. The length of time necessary for this to occur varies with the size of the animal that is killed. It may be from 24 hours to 3 or 4 days. The disappearance is due to the development of certain acids that cause the softening of the tissues. The albumin, which is contained in solution in the muscle fibers, is similar in composition to the albumen of eggs and milk, and it is affected by the application of heat in the cooking processes in much the same way.

10. GELATINE IN MEAT.--The gelatine that is found in meat is a substance very similar in composition to protein, but it has less value as food. It is contained in the connective tissue and can be extracted by boiling, being apparent as a jellylike substance after the water in which meat has been cooked has cooled. Use is made of this material in the preparation of pressed meats and fowl and in various salads and other cold-meat dishes. Some kinds of commercial gelatine are also made from it, being first extracted from the meat and then evaporated to form a dry substance.

11. FAT IN MEAT.--All meat, no matter how lean it appears, contains some fat. As already explained, a part of the fat contained in meat occurs in small particles so embedded in the muscle fibers as not to be readily seen, while the other part occurs in sufficient amounts to be visible. In the flesh of some animals, such as veal and rabbit, there is almost no visible fat, but in very fat hogs or fowls, one-third or one-half of the weight may be fat. Meats that are very fat are higher in nutritive value than meats that contain only a small amount of this substance, as will be observed on referring to the table of meat compositions in Fig. 1. However, an excessive amount of fat prevents the protein materials from digesting normally.

The quality of fat varies greatly, there being two distinct kinds of this material in animals. That which covers or lies between the muscles or occurs on the outside of the body just beneath the skin has a lower melting point, is less firm, and is of a poorer grade for most purposes than that which is found inside the bony structure and surrounds the internal organs. The suet of beef is an example of this internal fat.

Fat is a valuable constituent of food, for it is the most concentrated form in which the fuel elements of food are found. In supplying the body with fuel, it serves to maintain the body temperature and to yield energy in the form of muscular and other power. Since this is such a valuable food material, it is important that the best possible use be made of all drippings and left-over fats and that not even the smallest amount of any kind be wasted.

12. CARBOHYDRATE IN MEAT.--In the liver and all muscle fibers of animals is stored a small supply of carbohydrate in a form that is called glycogen, or muscle sugar. However, there is not enough of this substance to be of any appreciable value, and, so far as the methods of cookery and the uses of meat as food are concerned, it is of no importance.

13. WATER IN MEAT.--The proportion of water in meat varies from one-third to three-fourths of the whole, depending on the amount of fat the meat contains and the age of the animal. This water carries with it the flavor, much of the mineral matter, and some food material, so that when the water is removed from the tissues these things are to a great extent lost. The methods of cookery applied to meat are based on the principle of either retaining or extracting the water that it contains. The meat in which water is retained is more easily chewed and swallowed than that which is dry. However, the water contained in flesh has no greater value as food than other water. Therefore, as will be seen in Fig. 1, the greater the amount of water in a given weight of food, the less is its nutritive value.

14. MINERALS IN MEAT.--Eight or more kinds of minerals in sufficient quantities to be of importance in the diet are to be found in meat. Lean meat contains the most minerals; they decrease in proportion as the amount of fat increases. These salts assist in the building of hard tissues and have a decided effect on the blood. They are lost from the tissues of meat by certain methods of cookery, but as they are in solution in the water in which the meat is cooked, they need not be lost to the diet if use is made of this water for soups, sauces, and gravies.

15. EXTRACTIVES IN MEAT.--The appetizing flavor of meat is due to substances called extractives. The typical flavor that serves to distinguish pork from beef or mutton is due to the difference in the extractives. Although necessary for flavoring, these have no nutritive value; in fact, the body throws them off as waste material when they are taken with the food. In some methods of cookery, such as broiling and roasting, the extractives are retained, while in others, such as those employed for making stews and soups, they are drawn out.

Extractives occur in the greatest quantity in the muscles that the animal exercises a great deal and that in reality have become tough. Likewise, a certain part of an old animal contains more extractives than the same part of a young one. For these reasons a very young chicken is broiled while an old one is used for stew, and ribs of beef are roasted while the shins are used for soup.

Meat that is allowed to hang and ripen develops compounds that are similar to extractives and that impart additional flavor. A ripened steak is usually preferred to one cut from an animal that has been killed only a short time. However, as the ripening is in reality a decomposition process, the meat is said to become "high" if it is allowed to hang too long.