In France, the color of chicken eggs available for purchase is fairly constant, generally sporting shades that range from pink to more or less light beige. However, if you have the opportunity to travel, you will have noticed that the eggs that we buy in Germany or the United States are white. Curious to learn more about the color of eggs? Follow us for an overview of the issue!
How is the shell of the chicken egg made?
The eggshell is a very thin shell about 0.33mm thick, but stronger than is commonly believed. Microscopic observation of the structure reveals a composition based on crystals mineral salts -carbonates and phosphates of calcium and magnesium- which fit together and whose end is oriented towards the center of the egg. An egg is therefore structured to withstand very strong pressures, as soon as they are exerted lengthwise, that is to say on the most rounded parts. The solidity of the shell depends on several factors: the genetic origin of the hen, its age, its diet, its breeding conditions and its health.
The shell represents about 10% of the weight of the egg. It is made by the shell gland of the oviduct. It is designed to allow gas exchange but limit the penetration of microbes. It is divided into six layers. The last is called the “cuticle” and is only 10 µm thick.
What does the color of the eggs depend on?
The color of an egg depends on the breed of the hen which lays it and does not affect its taste. No chemical treatment needs to be applied to obtain eggs of a particular color: you just need to choose the right hen! Egg color is a product of the genetic characteristics of the laying hen. If a farm lets its hens of different breeds roam free and mix, the shades of the eggs will also mix. The selection of hens for a particular shade of egg is also practiced.
Before 1850, in France, the breeds present laid white-shelled eggs. After 1850, Asian breeds were imported and changed the color of the eggs to beige. Today is the Leghorn, also called Livorno, which is the most common breed of hens in the world, appreciated for its hardiness and, of course, its laying qualities with an average of 300 eggs per year, all very white. However, the color “eggshell”, eggshell in English, designates an off-white color tending towards pink or beige everywhere in the world.
Chocolate color and variations
Eggs from Marans breed hens and Penedesenca are the darkest. Chestnut brown in both hens, however, the Marans lays larger and shinier eggs. We are talking about extra red eggs, a beautiful warm brown color reminiscent of chocolate. A Marans hen raised in excellent conditions lays particularly strong eggs.
The Marans is a breed originating from the Poitevin marsh, the port city of Marans having given it its name. The breed was enriched in the 12th century through crossbreeding with fighting cocks brought by English sailors calling at La Rochelle.
In the Marans, the pigments which color the shell are deposited via the spongy tissue of the oviduct, 10 cm from the outlet. Once in the open, the layer dries quickly. A breeder relates the story of a Marans hen who had failed to expel an egg and kept it in the oviduct for several days: the layers of pigment had accumulated over 1 mm thick and the egg color approached black.
Marans exists in several varieties. It’s here Black Marans with copper hackle which lays the darkest eggs. But it is important to note that the color of the eggs is not constant, even for the same hen. It varies according to the position of the egg in the rosary. Indeed, a hen raised with respect for animal welfare does not lay nonstop all year round. This is of course not the case with factory-farmed hens. The laying of a hen is done according to a string, that is to say a cluster of eggs available in a row. Once the rosary is finished (but also when the hen is brooding), the hen does not lay any more, until the next rosary reaches maturity. The length of the shutdown varies depending on the breed, strain and hen itself. So the first egg of the rosary is darker and the others lighten a little bit by bit.
The deposition of pigments on the eggs is not always uniform. We talked about the fabric spongy of the oviduct. If you have ever painted with a sponge, you know that the result obtained is not homogeneous and creates variations, alternating more or less dense areas and forming spots. In the Marans, there are therefore three types of shells: uniform shells, pointillist shells and spotted shells. You guessed it, for the uniform version, the coloring is very homogeneous. The pointillist version is also common: the egg is dotted with small darker dots. This is the rarest spotted version: the spots are very brown and in slight relief
Other shell shades
The Araucana hen lays beautiful light blue-green eggs. As much as the Marans is the “goose that lays the golden eggs”, the Araucana is the “hen that lays the Easter eggs”. Unlike the Marans, the egg of the Araucana is colored throughout. Indeed, a Marans egg is white on the inside while that of the Araucana is the same color on the inside as on the outside.
It was in 2013 that researchers found the origin of the color of the shell. It is due to the action of a retrovirus integrated into the genetic heritage of this breed, a retrovirus also present in the genetic heritage of Chinese hens laying equally blue eggs. It captures biliverdin, a bile pigment resulting from the breakdown of hemoglobin, which is found integrated into the shell of the egg and gives it its particular color.
Besides their color, Araucana eggs are famous for their low fat content, so their consumption is indicated for people suffering from cholesterol. The Legbar, an English hen from the Araucana, also lays blue eggs.