What is an Egg?
Egg structure and composition.
| Weight | 58gms |
| Volume | 53cm3 |
| Specific Gravity | 1.09 |
| Long Axis | 5.7cm |
| Short Axis | 4.2cm |
| Long circumference | 15.7cm |
| Short circumference | 13.5cm |
| Surface Area | 68.2cm2 |
The shape may be described as oval.
The normal egg weight range is 35gms to 77gms.
| % of whole egg | |
| Shell | 10.5 |
| Yolk | 31 |
| White | 58.5 |
| Total Edible | 89.5 |
Egg anatomy
Shell:
- the first line of defence against the entry of bacteria
- can be brown or white; nutritional value of the egg is the same
- composed mainly of calcium carbonate
- approximately 8,000 to 10,000 tiny pores allow moisture and gases in (O2) and out (CO2)
Shell Membranes:
- there are two membranes on the inside of the shell
- one membrane sticks to the shell and one surrounds the white (albumen)
- the second line of defence against bacteria
- composed of thin layers of protein fibres
Germinal Disc:
- appears as a slight depression on the surface of the yolk
- the entry for the fertilization of the egg
White (Albumen):
- there are two layers: thin and thick albumen
- mostly made of water, high quality protein and some minerals
- represents 2/3 of the egg's weight (without shell)
- when a fresh egg is broken, the thick albumen stands up firmly around the yolk
Chalaza:
- a pair of spiral bands that anchor the yolk in the centre of the thick albumen
- the fresher the egg the more prominent the chalazas
- unnoticeable when the egg is cooked
Yolk Membrane (Vitelline Membrane)
- surrounds and holds the yolk
- the fresher the egg the stronger the membrane
Yolk:
- the egg's major source of vitamins and minerals, including protein and essential fatty acids
- represents 1/3 of the egg's weight (without shell)
- yolk colour ranges from light yellow to deep orange, depending on the hen's food
Air Cell:
- forms at the wide end of the egg as it cools after being laid
- the fresher the egg the smaller the air cell