It’s the age-old question, what came first, the chicken or the egg? No one will ever be able to answer with 100% certainty, but what we can answer with certainty is what is contained within a chicken egg, and how it is made. There are many parts of a chicken egg, and alot more to it than just the yolk, the white bit, and the shell.
There are many different parts of an egg, and we don’t even realise that many are there, as we tuck into our sunny side up eggs. But each part has a function to play, and is vital in keeping the egg fresh, as well as protecting the unhatched chick.
The Anatomy of a Chicken Egg
The main parts of a chicken egg that everyone knows are the shell, the albumin (egg white) and the yolk. However, as you can see from the image above, there are many more parts of a chicken egg. Many that you don’t know are there, and some you can see, if you look very closely, when using eggs for cooking.
Parts of a chicken egg:
This is the outer layer of an egg. It can vary in colour, from a dark brown, to a brilliant white, to shades of blue and green. The colours relates more to the breed of the bird, and not the contents of the shell.
It is made of calcium carbonate (CaCO3) and covered with thousands of tiny pores. An eggshell is a semipermeable membrane, allowing air and moisture to pass the pores via a process called osmosis. This is particularly relevant during the hatching stage. The humidity of the incubator is increased, to prevent the egg from drying out, and allow the chick to hatch slightly easier.
2. Bloom or Cuticle
A thin coating on the outside of the eggshell, which keeps out dust and bacteria. It keeps out the dust by sealing the pores on the eggshell. This also reduces moisture loss from the interior of the egg. It is easy to wash away, so care must be taken when cleaning eggs. In the Uk we don’t wash our eggs, ensuring that the bloom remains in place.
3. Outer and inner shell membranes
They are found immediately after the shell in the inner side of the egg. Both are partly made of keratin. Their primary function is to prevent bacteria from reaching the egg. They can often be seen when peeling a hard-boiled egg, as the thin piece of almost clear material that peels off the outside of the egg white.
4. Air Cell
After the egg has been laid by the chicken, the contents of the egg cool and contract, forming the airspace. The airspace is found between the outer and inner shell membranes at the larger end of an egg.
As the egg continues to age, moisture and carbon dioxide leave through the pores and air enters to replace them. During the incubation process, the air cell will increase in size. This can be seen by candling the egg.
Chalaza are spiral ropes of egg white that hold the yolk in place at the centre of the egg. There are 2 in each egg. These can often be seen when you crack an egg into a frying pan.
6. The Albumen / Egg White
The term albumen comes from the Latin word Albus, which means white. Albumen is primarily composed of water and contains around 40 different proteins. It has two layers; the outer albumen and the interior albumen.
The outer albumen is a thin fluid layer that is found next to the shell membrane, and it is usually very thin.
The interior albumen is thick and is found next to the egg yolk. It contains a large amount of riboflavin.
The 2 different types of albumen can often be seen when you crack an egg into a frying pan. It will sometimes appear as if the yolk is held up by a thicker egg white, which the outer albumen runs around the pan.
7. Vitelline Membrane
It is the clear casing that encloses the egg yolk. The strength of the vitelline membrane is essential in preventing egg yolk mottling.
8. Nucleus of Pander
The Nucleus of Pander provides the place for the chicken embryo to develop. The blastoderm (Or Germinal Disk see below) is an early stage of the embryo, present when the egg is laid. The blastoderm is attached to the Nucleus of Pander.
9. Germinal Disk
This is a small circular white spot found on the surface of the yolk. It is often visible with the naked eye. It is where the sperm enters the egg. After fertilization, the embryo develops from this place.
The yolk is the innermost part of the egg. Its colour is between yellow and deep orange, depending on the breed of the chicken and the type of the feed given to the chicken.
The yolk of an egg contains more proteins, vitamins fat, and minerals than the albumen. Just prior to hatching, a chick will absorb the yolk, and that will provide it with enough nutrients for the first 3 days of life.
That’s the 10 main parts of a chicken egg. There are more, and I would encourage all my readers who have an interest in eggs and hatching to go and research this further. Learning about the parts of a chicken egg can help you to improve your hatch rates, as well as ensuring the birds are happy and healthy. You can learn a lot about a flock, just from the eggs that they lay.
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