The mass of eggs can change, but the order of magnitude (an important notion in this entire
document) is about 60 grams.
The shell makes up some grams.
The inside of the egg is composed of two main parts:
- about 50 % of the egg’s total weight is known as the white, or albumen (look, it’s yellow): about 30
- about 50 % of the egg’s total weight is known as the yolk: about 30 grams.
The egg white is primarily made of proteins dissolved into water. More precisely, there are about 10
percent proteins, and 90 percent water.
It contains around 40 different proteins. The most abundant proteins are the globulins – mainly
ovalbumin and conalbumine, small coiled molecules.
The egg yolk is also composed of mainly proteins and water (50 percent), but in addition it contains
fats and cholesterol.
In a raw egg, the egg « white » is actually transparent. This is because all the proteins contained
within it are in their highly folded form. The individual proteins are so small that they do not interfere
much with visible light, like a wood stick in the middle of waves: if the diameter of the stick is smaller
than the wavelength, the wave goes on without much perturbance.
Effect of heating
In the presence of heat, or to a lesser extent acid and alkalis, the proteins are “denatured” and they
unwind. In this state, proteins can join together, or coagulate, and form a protein network, trapping the
water molecules and forming a solid gel. This is called a chemical gel, as the network is permanent
(unless, of course, you use strong chemicals in order to break the bonds between them).
The picture below shows such a network, but it does not explain why cooked egg white are white and
opaque; in reality, the edges of the network are made of many proteins, so that the size (diameter) of
these edges becomes larger than the wavelength of visible light.
Heating eggs to too high a temperature will cause some of the water contained to be squeezed out of