Egg white is the clear liquid contained within an egg. In chickens, it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms around fertilized or unfertilized egg yolks. The primary natural purpose of egg white is to protect the yolk and provide additional nutrition for the growth of the embryo .
Egg white consists primarily of about 90% water into which about 10% proteins are dissolved. Unlike the yolk, which is high in lipids (fats), egg white contains almost no fat, and carbohydrate content is less than 1%. Egg whites contain about 56% of the protein in the egg. Egg white has many uses in food as well as many other uses.
A raw egg with the round orange yolk in the center surrounded by the transparent yellow egg white.
Aerated egg whites are frequently employed in shaken cocktail recipes, such as this Ramos gin fizz, for textural and aesthetic purposes.
Beaten egg whites
Among animals which produce eggs, the yolk is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example because they are laid in situations where the food supply is sufficient or because the embryo develops in the parent's body, which supplies the food, usually through a placenta. Reproductive systems in which the mother's body supplies the embryo directly are said to be matrotrophic; those in which the embryo is supplied by yolk are said to be lecithotrophic. In many species, such as all birds, and most reptiles and insects, the yolk takes the form of a special storage organ constructed in the reproductive tract of the mother. In many other animals, especially very small species such as some fish and invertebrates, the yolk material is not in a special organ, but inside the egg cell.
The yolk of a chicken egg
Diagram of a fish egg; the yolk is the area marked 'C'
Comparison of an egg and an egg with a double-yolk (closed)
Comparison of an egg and an egg with a double-yolk (opened)