A common kitchen ingredient, the egg is as much a staple as sugar, flour, salt and milk. But eggs are small miracles. They can be eaten by themselves–fried, boiled, scrambled, poached, baked–or added to numerous other dishes, both sweet and savory, to provide flavor, color and consistency.

Cookies, cakes, soufflés, omelettes, custards and quiches cannot be made without breaking a few eggs.

Eggs are nutritional powerhouses, supplying protein; vitamins A, D and E; and minerals such as phosphorus, manganese, iron, calcium and zinc. Egg whites, also known as albumen, are among the most healthful of foods, being low in fat and high in protein. The yolks, on the other hand, contain the fat and cholesterol–and the most flavor.

Chicken eggs, by far the most commonly marketed and eaten eggs, are graded according to quality and size. Quality refers to freshness rather than nutrition. The highest-quality eggs, determined at time of packing, are AA, which have thick whites and firm, plump yolks. Grade A eggs fall only shortly behind in terms of quality. (Grade B eggs are low quality and rarely make it to the retail market.)

In terms of size, eggs are labeled jumbo, extra-large, large, medium, small and peewee. Most recipes are developed for large eggs and, while other sizes may be substituted, you may have to adjust the recipe. Fertile eggs from hens that have mated are considered a delicacy in some cultures, but these eggs offer no difference in nutritional value and do not keep as well.

Buy large AA eggs if possible. Look for those without cracks and with clean shells. All eggs destined for the commercial market have been carefully washed and coated with a natural mineral oil to prevent the introduction of bacteria.

Check the sell-by date, which should be as distant as possible.

Store eggs in a cold part of the refrigerator where the temperature is below 40ºF. Do not leave eggs at room temperature; a day on the countertop ages them as much as a week in the refrigerator.

Store eggs in their cartons. Don't transfer them to the egg racks found in some refrigerators. They may not stay cold enough because the door exposes them to changing temperatures as it opens and closes. The carton helps keep them cold and less likely to pick up refrigerator odors. Additionally, eggs should be stored with the broad ends up, which is how they are packed. This keeps the yolk centered.

Unbroken eggs refrigerated in their carton will keep for 5 weeks past their sell-by date. As they age, the whites will thin and become more transparent and the yolks will flatten, but the nutritional value of the eggs will not diminish. Use older eggs for baking, reserving the fresher ones for other cooking. Older egg whites are easier to whip up into voluminous meringue than absolutely fresh eggs, while fresh eggs are best for emulsified sauces such as hollandaise and mayonnaise.

Recipes will sometimes call for egg whites or egg yolks only, leaving you with leftover parts of eggs. Refrigerate uncooked egg whites in a tightly lidded glass or plastic container for up to 5 days. Refrigerate uncooked egg yolks in a glass or plastic container covered with a little water and tightly lidded for up to 2 days. Uncooked whole eggs removed from the shell can be stored in the same way and for the same length of time as egg yolks, but without the layer of water floated on top.

Freezing Eggs
Remove whole eggs from their shells and place in a rigid container. (Never freeze eggs in the shell.) Stir lightly to break the yolks; do not stir briskly or air bubbles may be incorporated. Cover, leaving only 1/2 inch of headroom, and freeze for up to 9 months.

To freeze egg whites only, combine them in a rigid container, cover and freeze for up to 1 year. To freeze egg yolks only, combine them, as with whole eggs, add a pinch of salt or sugar, seal and freeze for up to 9 months.

When thawed to room temperature, frozen egg whites will whip up more easily than fresh ones. Use thawed, frozen whole eggs and egg yolks as you would fresh, for baking or omelettes.

The best way to crack an egg is to tap it sharply against a flat surface such as a countertop–not a bowl rim. Holding the egg lengthwise over a container, break it in half, letting the white and yolk plop into it. If any shell gets into the bowl, use another piece of eggshell, a spoon or a fork to remove it.

Adapted from Williams-Sonoma Kitchen Companion: The A to Z Guide to Everyday Cooking, Equipment and Ingredients (Time-Life Books, 2000)