Egg

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A food product produced from poultry that is used as both an ingredient and a main dish for baked foods. Eggs have a hard shell of calcium carbonate enclosing a liquid white, a single yolk (or an occasional double yolk)and an air cell. The white or albumen is a clear liquid that turns to an opaque white when cooked or beaten. The yolk is orange to yellow in color, and becomes pale yellow when cooked to a solid form. The air cell increases in size as the egg ages and begins to lose moisture, thus decreasing in quality. Eggs can be cooked by boiling, poaching, frying, microwaving, or baking and they are one of the most common ingredients used for a variety of recipes. The types of eggs that are available for food preparation include chicken, duck, goose, turkey, and quail. Ostrich eggs are another variety of egg that is consumed, but are not readily available. Large in size, one ostrich egg equals 2 dozen standard size chicken eggs.

Chicken eggs are the most commonly eaten egg, which are typically classified and sold in four standard sizes: medium, large, extra large, and jumbo. They are also categorized into grades, which include AA, A or B, each grade being determined by an inspector considering both the interior and exterior quality. The outside must be smooth, well formed and consistent in color. Inside, the inspector grades the yolk structure, the density of the white and the size of the air cell. Higher grades such as AA will have a well formed yolk that is high in structure surrounded by a firm-textured white that holds closely to the yolk when it is broken open. Lower grades of eggs have yolks with less depth surrounded by thinner whites that have a tendency to spread out as they cracked open. Also, lower grades will not be as fresh as the higher grades, since they have lost more moisture and contain more air. When a recipe requires a chicken's egg, it is most always referring to "large" eggs.

The shells of chicken eggs may vary in color from white to brown, which is due to the breed of hen laying the egg. Despite the color variation, there is no difference in quality or nutritional value of the egg contents.