Egg Composition

Egg Composition

At first glance, an egg is made up of three parts: the yolk, white, and shell. Look a little closer, and you'll find not only a few other essential elements of the egg but a wealth of information about the make-up of the basic structure of the egg's components. 

A diagram of an egg showing the white, yolk, and chalaza

Parts of the Egg

  • White (aka albumen):
    The egg white exists mainly to protect the yolk from pathogens and to provide a layer of cushioning. Egg whites contain no fat or cholesterol but do provide other nutrients for a chicken embryo.

     - Water: an egg white is about 90% water.

     - Proteins: over half of an egg's total protein content comes from the white.

    The white is made up of 4 layers. The inner-most layer will lose viscosity as the egg ages. The white of a fresh egg will be thick and gelatinous, with a more opaque look than the outer white.
  • Chalaza:
    This is the tough, string-like structure found at either end of an egg. It anchors the yolk in place and is technically part of the egg white.
  • Yolk:
    Provides nutrients for the growing chick. 

     - Fat: all of an egg's total fat is found in the yolk; it is about 75% fat.

     - Lecithin: a naturally occurring emulsifier.

    Yolk color results from pigments in a hen's diet. Some farmers feed their chickens marigold petals or other supplements to achieve a bright orange yolk.
A diagram of an egg showing the shell, vitelline, and air cell
  • Vitelline:
    The thin membrane between the yolk and the white. It gets thinner as the egg ages, which is why it can be difficult to separate the yolk and the white cleanly when using older eggs.
  • Air Cell:
    You'll find the air cell on the wider end of the egg. Its size increases as the egg ages.
  • Shell:
    The egg's shell is porous, allowing air and moisture to pass through. 

     - Cuticle (aka Bloom): A naturally occurring, thin outer layer that protects the egg from dust and bacteria. This protective layer is removed by commercial processing in the US.

Albumen or Albumin?

Albumen refers to the egg white; albumin is the name for one of the proteins contained in egg whites. The chalaza is composed entirely of albumin.