For the causality dilemma, see Chicken or the egg. Humans and human ancestors have scavenged and egg white and cornstarch batter animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. Chickens and other egg-laying creatures are kept widely throughout the world and mass production of chicken eggs is a global industry.

1 million metric tons of eggs were produced worldwide from a total laying flock of approximately 6. Bird eggs have been valuable foodstuffs since prehistory, in both hunting societies and more recent cultures where birds were domesticated. In the Middle Ages, eggs were forbidden during Lent because of their richness, although the motivation for forgoing eggs during Lent was not entirely religious. The dried egg industry developed in the nineteenth century, before the rise of the frozen egg industry.

In 1878, a company in St. Louis, Missouri started to transform egg yolk and egg white into a light-brown, meal-like substance by using a drying process. In 1911, the egg carton was invented by Joseph Coyle in Smithers, British Columbia, to solve a dispute about broken eggs between a farmer in Bulkley Valley and the owner of the Aldermere Hotel. Early egg cartons were made of paper. Whereas the wild Asian fowl from which domesticated chickens are descended typically lay about a dozen eggs each year during the breeding season, several millennia of selective breeding have produced domesticated hens capable of laying more than three hundred eggs each annually, and to lay eggs year round.

Collected chicken eggs and quail eggs in a wicker basket. 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. The most commonly used bird eggs are those from the chicken, duck, and goose. Smaller eggs, such as quail eggs, are used occasionally as a gourmet ingredient in Western countries. The largest bird eggs, from ostriches, tend to be used only as special luxury food. Gull eggs are considered a delicacy in England, as well as in some Scandinavian countries, particularly in Norway.

In 2017, world production of chicken eggs was 80. The largest producers were China with 31. 3 million of this total, the United States with 6. 6 million, and Brazil and Russia with 2. A typical large egg factory ships a million dozen eggs per week. For the month of January 2019, the United States produced 9. 2 billion for table consumption and 1.

Americans are projected to each consume 279 eggs in 2019, the highest since 1973, but less than the 405 eggs eaten per person in 1945. During production, eggs usually are candled to check their quality. The size of its air cell is determined, and the examination also reveals whether the egg was fertilized and thereby contains an embryo. A raw chicken egg within its membrane, with the shell removed by soaking in vinegar. The shape of an egg resembles a prolate spheroid with one end larger than the other and has cylindrical symmetry along the long axis. An egg is surrounded by a thin, hard shell.

Thin membranes exist inside the shell. The larger end of the egg contains an air cell that forms when the contents of the egg cool down and contract after it is laid. Chicken eggs are graded according to the size of this air cell, measured during candling. A very fresh egg has a small air cell and receives a grade of AA.

As the size of the air cell increases and the quality of the egg decreases, the grade moves from AA to A to B. Eggshell color is caused by pigment deposition during egg formation in the oviduct and may vary according to species and breed, from the more common white or brown to pink or speckled blue-green. The eggshell membrane is a clear film lining the eggshell, visible when one peels a boiled egg. Primarily, it composed of fibrous proteins such as collagen type I.

Colorless and transparent initially, upon cooking it turns white and opaque. In chickens, it is formed from the layers of secretions of the anterior section of the hen oviduct during the passage of the egg. The yolk in a newly laid egg is round and firm. The resulting effect is a flattened and enlarged yolk shape. Yolk color is dependent on the diet of the hen.