Eggs are one of the world's most versatile foods. They can be prepared in many ways, from simple scrambled eggs to an elegant omelet. They provide an inexpensive and easy-to-prepare source of protein. In addition, eggs perform several important functions in cooking and baking.

• Beating or whipping eggs, especially egg whites, creates a foam that leavens angel food, sponge and chiffon cakes. Foams also provide volume to meringues and soufflés.
• Eggs function as a thickener for cooked foods, such as custards, puddings and sauces.
• Eggs function as an emulsifier, holding in suspension ingredients that do not naturally mix. For example, eggs hold oil and lemon juice (or vinegar) together in mayonnaise.
• Eggs bind ingredients together in foods, such as meatloaf, and help crumbs to adhere to food for frying.
• A combination of beaten egg and water or milk brushed on pastries or breads before baking produces a shiny glaze on the surface of the baked food.

There are many different types of eggs, but the chicken egg is most commonly used in cooking. The color of the egg shell (white or brown) is determined by the breed of the chicken. The color of the shell does not affect flavor, quality, nutrients or cooking characteristics of the egg.

Eggs are sold by grade and size. The grade of an egg is not the measure of its freshness. The grade is based on attributes, such as thickness of the white, firmness of the yolk and size of the interior air pocket. There are three grade classifications for eggs: AA, A and B. High grade eggs (AA) have firm, compact, round yolks with thick whites.

There are six size classifications for eggs: jumbo, extra large, large, medium, small and peewee. The classification is determined by the minimum weight allowed per dozen. For example, a dozen large eggs weighs a minimum of 24 ounces. Any size egg can be used for scrambling, frying, poaching, etc. However, most recipes that call for eggs were developed using large eggs. Unless otherwise specified in the recipe, always use large eggs.

Select clean, unbroken grade AA or A eggs from refrigerated cases. Purchase eggs as fresh as possible. The USDA requires that egg cartons display the packing date. The date is indicated by a number representing the day of the year. For example, January 1 is day 1 and December 31 is day 365. An expiration date (month and day) may also be displayed. This is the last sale date and must not exceed 30 days after the packing date.

Refrigerate eggs immediately after purchasing. To prevent them from absorbing odors from other foods, store them in the original carton. For best flavor, use eggs within a week after purchasing. However, they will keep for five weeks after the packing date without loss of nutrients or functional properties. Longer storage may affect the appearance of fried and poached eggs. For hard cooking, choose eggs that are at least a week old. They will peel more easily.

Eggs separate more easily when cold. To separate an egg yolk from a white, gently tap the egg in the center with a table knife or against a hard surface, such as the side of a bowl. Gently break the egg in half over a small bowl. Holding a shell half in each hand, gently transfer the yolk back and forth between the two shell halves, allowing the white to drip into the bowl. Place the yolk into another bowl. An egg separator is a useful tool that will facilitate this job. See Tool for additional information.

Egg whites reach the fullest volume if they are allowed to stand at room temperature for 30 minutes before beating. Egg whites must be completely free of egg yolk. To remove any traces of yolk, use a cotton swab or the corner of a paper towel. Always check that the bowl and beaters are clean and dry. The smallest trace of yolk, fat or water can prevent the whites from obtaining maximum volume. Do not use plastic bowls, because they may have an oily film even after repeated washings.

Beat the egg whites slowly with an electric mixer at low speed until the whites are foamy. Then increase the speed to high. Add a pinch of salt or cream of tartar to stabilize the foam. Beat until the whites are stiff but not dry. Immediately fold beaten egg whites into another mixture so volume is not lost.

The basic principle of egg cookery is to cook eggs until the whites are completely coagulated (thickened) and the yolks begin to thicken. Yolks should not be runny, but they should not be hard either. Cook slowly over gentle heat, and once cooked, serve immediately. Keep in mind that too much heat will result in tough, rubbery eggs. The following are guidelines for basic egg-cooking methods.

For hard-cooked eggs, place the eggs in a single layer in a saucepan. Add cold water to cover the eggs by one inch. Cover and bring to a boil over high heat. Remove from the heat. Let stand 15 minutes. Immediately pour off the water, cover with cold water or ice water and let stand until cooled.

To peel hard-cooked eggs, crack the shell all over by tapping the egg on the counter. Gently roll the egg across the counter with the palm of your hand to loosen the shell. Peel away the shell under cold running water.

For soft-cooked eggs, place the eggs in a single layer in a saucepan. Add enough cold water to cover the eggs by one inch. Bring to a boil over high heat. Reduce the heat so the water is just below simmering. Cover and cook 4 to 5 minutes, depending on desired doneness. Remove from the heat and drain. Immediately run cold water over the eggs or place in ice water until cool enough to handle.

To serve out of the shell, crack the shell through the middle with a knife. With a teaspoon, scoop the egg out of each shell half into a serving dish. To serve in an egg cup, place the egg in the egg cup, small end down. Slice off the large end of the egg with a small knife or egg scissors and eat from the shell with a spoon.

For fried eggs, melt 1 to 2 tablespoons butter or margarine over medium heat in an 8-inch skillet, swirling to coat the bottom of the skillet. Break two eggs into the pan. Cook 2 to 4 minutes spooning butter over eggs several times. Or, cover and cook 2 to 4 minutes or until the eggs are set. Makes 1 serving.

For scrambled eggs, combine 2 eggs, 2 tablespoons milk, salt and black pepper to taste in a small bowl. Beat with a fork or until completely blended. Melt 1 teaspoon butter or margarine in a 7- to 8-inch skillet over medium-low heat. Pour in the egg mixture. As the mixture begins to set, gently stir it with a wooden spoon, lifting the cooked portions and letting the uncooked egg flow underneath. Cook until the eggs are just set, but still moist looking. Do not stir the eggs constantly. Makes 1 serving.

For poached eggs, bring 2 to 3 inches of water, milk, broth or other liquid to a boil over medium-high heat in a medium saucepan. Reduce the heat to keep the water at a simmer. Break 1 egg into a small dish or custard cup. Holding the dish close to the surface of the water, carefully slip the egg into the water. Repeat with another egg. Cook 3 to 5 minutes or until the yolks are just set. Remove the eggs from the saucepan with a slotted spoon and drain on paper towels. Makes 1 serving.

A very small percentage of American eggs are contaminated with salmonella, a bacteria that causes a type of food poisoning. To avoid illness caused by this bacteria, follow these simple guidelines

• Purchase eggs only from stores that display them in refrigerated units.
• Keep eggs refrigerated. If a recipe calls for room temperature eggs, remove only the number of eggs needed and let them stand on the counter for no more than 30 minutes before using.
• Do not eat raw eggs or foods containing raw eggs, such as homemade eggnog and mayonnaise. Avoid lightly cooked eggs. Whites should be set and yolks should be thickened. A temperature of 160°F kills salmonella.
• After handling raw eggs, wash your hands before touching other food or equipment. Keep equipment and counter surfaces clean.
• At buffets and picnics, keep cold foods cold and hot foods hot.

See Food Safety for additional information.

Developed for use in commercial and food service applications, processed liquid egg products are now available in cholesterol-free versions for the retail consumer. They are available refrigerated and frozen. Cholesterol-free products generally contain egg whites, nonfat milk, emulsifiers, stabilizers, gums and color. These products can be substituted for whole eggs in cooking and baking. Pasteurized liquid eggs that contain both whites and yolks are also available. Although these are not cholesterol-free, they are a good choice for use in lightly cooked egg dishes or homemade eggnog.