molecules of water caught in the net. As the egg cooks, the protein network tightens, squeez-
ing out moisture, and the egg becomes opaque. The longer you cook the egg, the tighter the
network will be. If you cook the egg too long, the protein network will contract strongly
enough to force out all the moisture. That is why overcooked egg custards run and why
overcooked eggs are rubbery.
If you mix eggs with milk or water before you cook them, the molecules of liquid will
surround and separate the egg’s protein molecules so that it takes more energy (higher heat)
to make the protein molecules coagulate. Scrambled eggs made with milk are softer than
plain scrambled eggs cooked at the same temperature.
When you boil an egg in its shell, the air inside expands and begins to escape through
the shell as tiny bubbles. Sometimes, however, the force of the air is enough to crack the
shell. Since there’s no way for you to tell in advance whether any particular egg is strong
enough to resist the pressure of the bubbling air, the best solution is to create a safety vent
by sticking a pin through the broad end of the egg before you start to boil it. Or you can
slow the rate at which the air inside the shell expands by starting the egg in cold water and
letting it warm up naturally as the water warms rather than plunging it cold into boiling
water—which makes the air expand so quickly that the shell is virtually certain to crack.
As the egg heats, a little bit of the protein in its white will decompose, releasing sulfur
that links up with hydrogen in the egg, forming hydrogen sulfide, the gas that gives rot-
ten eggs their distinctive smell. The hydrogen sulfide collects near the coolest part of the
egg—the yolk. The yolk contains iron, which now displaces the hydrogen in the hydrogen
sulfide to form a green iron-sulfide ring around the hard-cooked yolk.
How Other Kinds of Processing Affect This Food
Egg substitutes. Fat-free, cholesterol-free egg substitutes are made of pasteurized egg whites,
plus artificial or natural colors, flavors, and texturizers (food gums) to make the product look
and taste like eggs, plus vitamins and minerals to produce the nutritional equivalent of a full
egg. Pasteurized egg substitutes may be used without additional cooking, that is, in salad
dressings and eggnog.
Drying. Dried eggs have virtually the same nutritive value as fresh eggs. Always refrigerate
dried eggs in an air- and moistureproof container. At room temperature, they will lose about
a third of their vitamin A in six months.
Medical Uses and/or Benefits
Protein source. The protein in eggs, like protein from all animal foods, is complete. That is,
protein from animal foods provides all the essential amino acids required by human beings.
In fact, the protein from eggs is so well absorbed and utilized by the human body that it is
considered the standard by which all other dietary protein is measured. On a scale known
as biological value, eggs rank 100; milk, 93; beef and fish, 75; and poultry, 72.
Eggs