Eggs are marvelous. They are used in so many products and in so many ways. They provide structure and mouth feel; they provide moisture and nutritional value. Baking would be dramatically different without the egg.
There are three parts to the egg:
The shell is fragile and porous. It is important to remember that eggs will absorb flavors and odors through the shell and therefore must be protected from strong smelling substances and unsanitary surfaces. A tainted egg will spoil your product.
The yolk is high in both fat and protein and is a natural emulsifier. The white is primarily albumin protein. It is clear and soluble before it is cooked. It contains sulfur and becomes odorous when old.
About 75% of the egg by weight is water. The remaining portion is nearly equal parts fat and protein. A large egg weighs 1 2/3 ounce without the shell with the yolk weighing two-thirds of an ounce and the white, one ounce. A medium egg without the shell weighs about 1.45 ounces and a small egg weighs about 1 1/4 ounces. You can do the math but about 3 1/2 medium eggs equal three large eggs.
Eggs are a potential source of salmonella contamination. The American Egg Board estimates that only one in 20,000 eggs is contaminated. Still, it is recommended that you do not use raw eggs in your food and that egg products be cooked to 160 degrees. Always wash your hands after handling eggs and sanitize any work surfaces where raw eggs may have been used.
The egg industry is conscientious and regulated and it is very rare to find an inferior or rotten egg in a carton. It is not rare to find broken or cracked shells. When you open a carton and find a cracked egg, discard it since a crack creates an easy avenue for bacteria to enter.
Always buy eggs that are graded A or AA. You can determine the quality of the eggs from your refrigerator just as an inspector does. Open an egg onto a flat surface. If the egg is compact with a plump yolk, it is fresh. If the chalazae, the white strands in the egg white, are prominent, the egg is fresh.
Eggs kept in the coldest part of the refrigerator keep up to five weeks, though we plan on using our eggs within two weeks. Fresh eggs make for more stable egg white foams. Eggs become more alkaline as they age and may have a minor affect on the function of chemical leaveners.
Because the shells are porous, eggs will lose moisture over time. Eggs packaged for consumers are given a mineral oil bath to help seal the shells, reduce the moisture loss, and protect the egg from odors. Do not wash your eggs since doing so will remove the protective mineral oil covering.
Many recipes call for eggs at room temperature. Rather than leaving your eggs on the counter to warm, simply place them in a bowl of warm water for a few minutes.