Foods, their selection and preparation

The egg consists of three distinct parts: the shell, the white, and the yolk. In addi¬ tion to the shell, there are two shell mem¬ branes surrounding the egg contents. As the egg cools and the contents contract, an air cell is formed between these two membranes, usually at the large end of the egg. One can easily distinguish three types of white: the thick portion, the thin portion, and the chalazae, or cords. On the yolk can be seen the germinal disk commonly called the "germ spot." The shell makes up approximately 1 1 per cent, the white 58 per cent, and the yolk 31 per cent of the whole egg. These percentages vary with eggs from different sources, but there is little variation in day-old eggs. The shell is heavier when there is an abundance of calcium in the diet of the hens or when the hens are fed a diet rich in vitamin D. Eggs vary in weight or size according to the breed and age of the hen. The average weight of a large egg in the shell is about two ounces (56 grams), or eight eggs to the pound. Medium-sized eggs weigh 20 ounces to the dozen and the smallest eggs about 18 ounces. The Shell. The color of the shell varies from white to brown, depending upon the breed of hen. Some foreign breeds produce eggs with a bluish shell. In some markets white-shelled eggs receive a higher price than brown-shelled ones, and in other markets brown-shelled eggs are preferred and cost more. However, there is no difference in composition, palatability, or cooking quality of eggs due to the color of the shell. Shell color is a breed characteristic and is not a guide to the color of the yolk. The shell is composed chiefly of the car¬ bonates and phosphates of lime. It is porous in structure and, therefore, permits the es¬ cape of moisture with absorption of air, and, when eggs are not properly handled, the entrance of microorganisms. The shell nor¬ mally is coated with a mucilaginous substance which helps protect the contents from evap¬ oration and contamination. The White. Fresh egg white has an opal¬ escent appearance, and when the egg is broken onto a flat surface the white next to the yolk is thick and viscous and tends to hold its shape, while that on the outer edge is less viscous and thinner. As the egg ages or if it is held at too warm a temperature, the thick white tends to become thin. In general, eggs with thick white beat up [95] Table XIX • Proximate Composition of Eggs Water Protein Fat Ash Whole egg, E. P.1 . White . Yolk . Per cent 73.70 87.77 49.00 Per cent 13.40 10.00 16.70 Per cent 10.50 0.05 31.90 Per cent 1.00 0.82 1.90 better than those with thin. Certain hens consistently produce eggs with thin or watery whites.