Egg (food)

Eggs are laid by females of many different species, including birds, reptiles, amphibians, and fish, and have been eaten by mankind for thousands of years.[1] Bird and reptile eggs consist of a protective eggshell, albumen (egg white), and vitellus (egg yolk), contained within various thin membranes. Popular choices for egg consumption are chicken, duck, quail, roe, and caviar, but the egg most often consumed by humans is the chicken egg, by a wide margin. Egg yolks and whole eggs store significant amounts of protein and choline,[2][3] and are widely used in cookery. Due to their protein content, the United States Department of Agriculture (USDA) categorizes eggs as Meats within the Food Guide Pyramid.[2] Despite the nutritional value of eggs, there are some potential health issues arising from egg quality, storage, and individual allergies. Chickens and other egg-laying creatures are widely kept throughout the world, and mass production of chicken eggs is a global industry. In 2009, an estimated 62.1 million metric tons of eggs were produced worldwide from a total laying flock of approximately 6.4 billion hens.[4] There are issues of regional variation in demand and expectation, as well as current debates concerning methods of mass production, with the European Union's ban on battery farming of chickens.Bird eggs are a common food and one of the most versatile ingredients used in cooking. They are important in many branches of the modern food industry.[7] The most commonly used bird eggs are those from the chicken. Duck and goose e gs, and smaller eggs, such as quail eggs, are occasionally used as a gourmet ingredient, as are the largest bird eggs, from ostriches. Gull eggs are considered a delicacy in England,[11] as well as in some Scandinavian countries, particularly in Norway. In some African countries, guineafowl eggs are commonly seen in marketplaces, especially in the spring of each year.[12] Pheasant eggs and emu eggs are perfectly edible, but less widely available.[11] Sometimes they are obtainable from farmers, poulterers, or luxury grocery stores. Most wild birds eggs are protected by laws in many countries, which prohibit collecting or selling them, or permit these only during specific periods of the year.[11] See also fish eggs. Cooking issues Egg white coagulates, or solidifies, when it reaches temperatures between 144 and 149F (62.2 and 65C).[13] Egg yolk coagulates at slightly higher temperatures, between 149 and 158F (65 and 70C).[13] If a boiled egg is overcooked, a greenish ring sometimes appears around egg yolk due to the iron and sulfur compounds in the egg. It can also occur with an abundance of iron in the cooking water.[citation needed] The green ring does not affect the egg's taste; overcooking, however, harms the quality of the protein.[citation needed] Chilling the egg for a few minutes in cold water until it is completely cooled may prevent the greenish ring from forming on the surface of the yolk. Cooking also increases the risk of atherosclerosis due to increased oxidization of the cholesterol contained in the egg yolk.