The idea that brown chickens lay brown eggs and white chickens lay white eggs is a common assumption made by many consumers. While a visual correlation often exists between a hen’s feather color and her egg color, the relationship is a generalization. The actual determinant of eggshell color is the hen’s genetics and the biochemical processes that occur during egg formation. Feather color is merely a coincidental trait in many domesticated breeds.
The True Indicator of Egg Color
The color of a hen’s feathers is not the direct cause of her egg’s color; instead, both traits are linked by the chicken’s breed and genetic blueprint. A more reliable visual indicator of the egg color a hen will produce is the color of her earlobes. Hens with white earlobes tend to lay white eggs, while those with red or brown earlobes lay eggs in shades of brown or other colors.
This correlation is a simplified rule of thumb, but it holds true for many common egg-laying breeds. For instance, the White Leghorn breed, known for its white earlobes and white feathers, produces white-shelled eggs. Conversely, breeds such as the Rhode Island Red and the Orpington, which have reddish-brown feathers and red earlobes, are layers of brown eggs. The ability to produce a specific egg color is determined by the hen’s genetics, which dictates whether pigments are deposited onto the shell.
The Biological Process of Shell Pigmentation
All chicken eggs initially begin with a white shell, composed primarily of calcium carbonate. The color is integrated only during the final hours of the 24-to-26-hour egg-laying cycle, when the egg is in the shell gland (uterus). Specific pigments, determined by the hen’s breed, are synthesized and applied to the shell within this gland.
The brown color on eggshells comes from a pigment called Protoporphyrin IX, which is a byproduct of hemoglobin breakdown. This brown pigment is deposited mainly onto the outermost layer of the shell. In contrast, blue eggshells, such as those laid by Ameraucana breeds, are colored by Oocyanin. Unlike the brown pigment, Oocyanin penetrates through all layers of the shell, making the inside and outside of a blue eggshell the same color.
The intensity of the final eggshell color is influenced by the amount of pigment deposited and the time the egg spends in the shell gland. If a hen is stressed or lays eggs rapidly, the pigment application may be lighter, resulting in a paler shade of brown. The placement and concentration of the pigment determine the final shade, which can range from a pale tan to a deep chocolate brown or result in speckling.
Nutritional Content and Egg Color
The color of an eggshell is a superficial characteristic that has no direct impact on the egg’s nutritional profile or flavor. Many consumers believe brown eggs are healthier or taste richer, but the contents—the albumen and the yolk—are identical in protein, vitamins, and fat content regardless of the shell color. Both white and brown eggs provide about 70 calories and six grams of protein in a large size.
Any slight variations in the egg’s nutritional value or flavor are primarily due to the hen’s diet and her living conditions, not the shell color. For example, a hen fed a diet rich in omega-3 fatty acids will produce eggs with higher levels of those beneficial fats, regardless of the egg color. Therefore, the choice between white and brown eggs is largely a matter of personal preference or a reflection of the price difference associated with the specific breeds that lay them.