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.
[Illustration: Fig 1.]
BEEF Fuel value per pound
Chuck, medium fat 735
Loin, medium fat 1040
Ribs, medium fat 1155
Round, very lean 475
Round, medium fat 895
Round, very fat 1275
Rump, medium fat 1110
VEAL
Breast, medium fat 740
Leg, medium fat 620
Loin, medium fat 690
LAMB
Leg, medium fat 870
MUTTON
Leg, medium fat 900
PORK
Ham, fresh, medium fat 1345
Ham, smoked 1675
Loin 1455
Bacon, medium fat 2795
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.