Eggs: Don’t judge them by the shell

By C. Claiborne Ray / New York Times News Service

Q: Is there any nutritional difference between brown and white eggs? What accounts for the difference in shell color?

A: There is no discernible difference in nutritional value, said Tro Bui, a visiting fellow in animal science at Cornell University. Brown eggs in general may have more omega-3 fatty acids, but the difference is tiny, he said. There is no difference in yolk color or taste.

Genes determine shell color, Bui said. White-feathered chickens with white earlobes lay white eggs; red or brown ones with red earlobes lay brown eggs; and the Ameraucana breed, also known as the Eastern egg chicken, lays eggs with blue shells.

Shell quality does not differ by breed, though younger chickens lay eggs with harder shells. Brown-egg chickens tend to be larger and cost more to feed and raise, so white eggs are more cost-efficient.

The type of feed can affect the egg’s nutritional content as well as its yolk color, Bui said.

An egg’s content and shell are formed at opposite ends of the reproductive tract. The pigments that determine shell color are oocyanin, a byproduct of bile production, in blue eggs, and porphyrins, a class formed by the breakdown of blood cells, in brown eggs.