Food is preserved by the following processes: (1) drying, (2) smoking, (3) salting, (4) freezing, (5) refrigerating, (6) sealing, (7) addition of antiseptic and preservative substances.
DRYING.
Drying in the sun and before a fire is the usual method employed by housekeepers. Fruits and vegetables, meat and fish may be preserved by drying, the latter with the addition of salt.
SMOKING.
Smoking is chiefly applied to beef, tongue, bacon, ham, and fish, which are hung in a confined chamber, saturated with wood smoke for a long time until they absorb a certain percentage of antiseptic material, which prevents the fat from becoming rancid, and the alb.u.men from putrefying. Well smoked bacon cut thin and properly cooked is a digestible form of fatty food, especially for tubercular patients.
Smoking improves the digestibility of ham.
SALTING.
Salting is one of the oldest methods of preserving food. The addition of a little saltpetre helps to preserve the color of the meat. Brine is frequently used to temporarily preserve meat and other substances.
Corned beef is a popular form of salt preservation. All salted meats require long, slow cooking. They should always be placed in cold water and heated gradually in order to extract the salt. Salt meats are less digestible and not quite so nutritious as fresh meats.
FREEZING.
Food may be kept in a frozen condition almost indefinitely, but will decompose very quickly when thawed, hence the necessity for cooking immediately. Frozen meat loses 10 per cent. of its nutritive value in cooking.
REFRIGERATING.
This process does not involve actual freezing, but implies preservation in chambers at a temperature maintained a few degrees above freezing point. This method does not affect the flavor or nutritive value of food so much as freezing.
SEALING.
Sealing is accomplished not only in the process of canning but by covering with substances which are impermeable. Beef has been preserved for considerable time by immersing in hot fat in which it was allowed to remain after cooling.
CHEMICALS.
Chemicals are sometimes used in the preservation of food, but the other methods are safer.
CHAPTER V.
Foods Containing Protein, or Nitrogenous Matter.
Animal foods contain nutritive matter in a concentrated form, and being chemically similar to the composition of the body is doubtless the reason why they a.s.similate more readily than vegetable foods, although the latter are richer in mineral matter. The most valuable animal foods in common use are meat, eggs, milk, fish, gelatin and fats.
MEAT.
Meat is composed of muscular tissue, connective tissue or gristle, fatty tissue, blood-vessels, nerves, bone, etc. The value of meat as food is due chiefly to the nitrogenous compound it contains, the most valuable being the alb.u.minoids: the gelatinoid of meat is easily changed into gelatin by the action of hot water. Gelatin when combined with the alb.u.minoids and extractives has considerable nutritive value.
Extractives are meat bases, or rather meat which has been dissolved by water, such as soup stock and beef tea. The object in cooking meat is to soften and loosen the tissue, which renders it more easily digested. Another object is to sterilize or kill any germs which may exist and to make it more palatable. The digestibility of meat is influenced by the age of the animal killed and the feeding. The following table is given as an average of the digestibility of animal foods:--
TABLE OF COMPARATIVE DIGESTIBILITY.
_Commencing with the most digestible and ending with the least digestible of meats and other animal foods._ (Thompson.)
Oysters.
Soft cooked eggs.
Sweetbread.
Whitefish, etc.
Chicken, boiled or broiled.
Lean roast beef or beefsteak.
Eggs, scrambled, omelette.
Mutton.
Bacon.
Roast fowl, chicken, turkey, etc.
Tripe, brains, liver.
Roast lamb.
Chops, mutton or lamb.
Corn beef.
Veal.
Duck and other game.
Salmon, mackerel, herring.
Roast goose.
Lobster and crabs.
Pork.
Fish, smoked, dried, pickled.
Cooking affects the digestibility of meat, which is evident from the figures given in the following table (Church):--
TIME OF DIGESTION.
--------------------+---------------- | Hours.
--------------------+---------------- Beef, raw | 2 Beef, half boiled | 2-1/2 Beef, well boiled | 2-3/4 to 3 Beef, half roasted | 2-3/4 to 3 Beef, well roasted | 2-1/4 to 4 Mutton, raw | 2 Mutton, boiled | 3 Mutton, roasted | 3-1/4 Veal, raw | 2-1/2 Pork, raw | 3 Pork, roasted | 5-1/4 Fowl, boiled | 4 Turkey, boiled | 2-1/2 Venison, broiled | 1-1/2 --------------------+----------------
It may be well to add here that animal food is more digestible when cooked between 160 and 180 F. than at a higher temperature.
Cooking of Meat.
_(For more general information, see Recipes.)_
In boiling meat two principles must be considered, the softening of the fibre and preserving of the juices. If the meat alone is to be used it should be placed in sufficient boiling water to completely cover, and kept at boiling point (212 F.) for at least ten minutes, so as to harden the alb.u.men and prevent the escape of the juices. The temperature should then be allowed to fall to simmering point (175 F.). If the water is kept boiling it will render the meat tough and dry. If the juice is to be extracted and the broth used, the meat should be placed in cold water; if bones are added they should be cut or broken into small pieces in order that the gelatin may be dissolved. If the water is heated gradually the soluble materials are more easily dissolved. The alb.u.men will rise as a sc.u.m to the top, but should not be skimmed off, as it contains the most nutriment and will settle to the bottom as sediment.
STEWING.
If both meat and broth are to be used the process of cooking should be quite different. In stewing, the meat should be cut into small pieces, put into cold water in order that the juices, flavoring material and fibre may be dissolved. The temperature should be gradually raised to simmering point and remain at that heat for at least three or four hours, the vessel being kept closely covered. Cooked in this way the broth will be rich, and the meat tender and juicy. Any suitable flavoring may be added. This is a good method for cooking meat containing gristle.
ROASTING AND BROILING.
When the meat alone is to be eaten, either roasting, broiling or frying in deep fat is a more economical method, as the juices are saved. The shrinkage in a roast of meat during cooking is chiefly due to a loss of water. A small roast will require a hotter fire than a larger one, in order to harden the exterior and prevent the juices from escaping. Meat is a poor conductor of heat, consequently a large roast exposed to this intense heat would become burned before the interior could be heated. The large roast should be exposed to intense heat for a few minutes, but the temperature should then be reduced, and long steady cooking allowed.
Broiling (see broiling in previous chapter, p. 19.)