Eggs.
—Eggs are a common article of diet throughout the world. The eggs of domesticated fowls are those which are principally used for food, though the eggs of wild fowls, and birds and reptiles are also edible but on account of the difficulty of getting them and their rarity are not to be considered as a commercial article. The chief sources of supply are the eggs of chickens, ducks, and geese. Chicken eggs are by far the most important, duck eggs the next important, and goose eggs the least important. The eggs of fish also constitute an article of food of considerable value and are extensively used. For instance the fresh eggs of shad are used in large quantities during the whole of the shad season and are often kept in cold storage for use at other times. The eggs of sturgeon are used extensively in the fresh state and when pickled as caviar are highly esteemed throughout the world. These two kinds of eggs are probably the most important of fish eggs used for food purposes. Chicken eggs vary greatly in size according to the age and variety of the fowl. The average weight of chicken eggs is 680 grams per dozen. They vary also in color from pure white to a brownish yellow. Duck eggs are larger and also variegated in color. The average weight of duck eggs is 847.2 grams per dozen. Goose eggs are the largest of the three varieties, varying also in color. They weigh on an average 2284.8 grams per dozen. Eggs also vary greatly in shape, being generally ovoid but some being much more spherical than others according to the species of the fowl and variety. The number of eggs which a chicken will lay varies greatly. Attempts have been made, with great success, at experiment stations, to develop chickens with high laying powers. A hen which will produce over 200 eggs a year is regarded as a high-grade fowl for egg-producing purposes. Eggs are produced more abundantly during the early spring and summer than during the winter months. One of the purposes of scientific egg producing is the development of fowls that will produce eggs more evenly throughout the whole year, thus avoiding the very great depression in the price of eggs in the spring and the excessively high price of eggs in the winter.
Composition of Eggs.
—A large number of eggs have been analyzed in all quarters of the world and found to vary but little in composition in different localities, and very little also in regard to the variety of the fowl. The egg consists essentially of two portions,—an external highly albuminous portion known as the white and an internal colored portion, yellow or reddish in tint, known as the yolk. The white of an egg is composed almost entirely of albumin partially dissolved in water. The yolk of the egg is composed of albumin, fat, and a phosphorus-bearing material of high nutritive value known as lecithin. The yolk of an egg is a much richer food product than the white, containing in addition to the nitrogenous element the fat and mineral bodies necessary to nutrition. Both the white and yolk of an egg are composed principally of water as will be seen by the following analytical data:
COMPOSITION OF EDIBLE PART OF EGGS.
| Water. Percent. | Protein. Percent. | Fat. Percent. | Ash. Percent. | Calories. Per pound. | |
|---|---|---|---|---|---|
| Hen, | 73.7 | 13.4 | 10.5 | 1.0 | .... |
| Duck, | 70.5 | 13.3 | 14.5 | 1.0 | 985 |
| Goose, | 69.5 | 13.8 | 14.4 | 1.0 | 985 |
| Turkey, | 73.3 | 13.4 | 11.2 | 0.9 | 850 |
Preservation of Eggs.
—Freshly laid eggs may be preserved for several days without any notable deterioration by keeping in a cool place. The temperature of preservation should be as nearly the freezing point as can be secured. The vital processes are continually going on in a fresh egg and hence there is a development of a certain degree of heat due to these activities. For this reason eggs can be placed in an atmosphere below the freezing point of water without being frozen. An additional reason for this is found in the fact that the water which is present in eggs holds the albumin and other bodies in solution and the freezing point of a solution is always lower than that of the solvent alone. For domestic purposes where refrigerating establishments are not available the fresh eggs should be kept in a cool dark place where the temperature is not allowed to go above 50 or 60 degrees. At a higher temperature than this fresh eggs lose their freshness in a remarkably short time. The porous nature of the shell is a condition which favors the deterioration of the egg by the admission of air and microbes into the substance of the egg itself.
The preservation of eggs is, therefore, materially assisted by coating the egg artificially with a varnish or film of some kind which renders the egg impervious to air and water. One of the cheapest, simplest, and best of these coatings, as has already been noted, is soluble glass. This is produced by dissolving the chemical substance known as silicate of soda in water, and dipping the egg into the solution, removing and allowing to dry. The silicate of soda which is thus left in a thin film over the surface of the egg penetrates and stops the pores and renders the egg shell practically impervious both to air and water. This material has the property of becoming totally insoluble in water when it has once been dried so that even if the egg is afterwards subjected to rain or water in any form the film is not removed. Many other methods of coating eggs have been employed and are dependent upon the same principle but are perhaps not so effectual and simple as the inexpensive method above described.