What's the Difference Between Eggs of Different Colors?

Brown, white, blue, or green: Chicken eggs come in a spectrum of colors, but they all cook up the same. Learn what makes eggs different colors in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain Stuff from How Stuff Works, Hi brain Stuff,
Lauren vocal Bomb. Here Peru's the egg section of a
grocery store of Farmer's Market, and you'll notice cartaons of
eggs separated into white and brown, and sometimes even green
or blue eggs. But once they arrive scrambled on a
plate or baked into a cake, it's tough to tell
the difference. So what is the difference between eggs with

(00:25):
shells of different colors? This isn't a situation like rice
or flour. Brown eggs are not more natural, and white
eggs have not been dcolored with bleach. Both varieties occur
completely naturally, as do bluish green chicken eggs. But really
all chicken eggs are the same on the inside. So
what causes different egg colors among the same type of bird.

(00:45):
We spoke with Dr Justin Fowler. We cannot make this up,
Who's a professor at the University of George's Poultry science department.
He said, the different colors, or the presence of spots
or speckling, come down to the genetics of the bird.
Leghorn chickens, which make up most of the commercial egg
industry in the United States lay white eggs, while Orphington's

(01:06):
or plymouth rocks will lay brown eggs. The Amerquana breed
has a pigment that's able to permeate the whole egg
shell and make blue colored eggs that are colored on
both the inside and outside of the shell. So there
you go. I want to know whether a specific chicken
will pop out a white egg or a colored egg.
Examine the chicken's earlobe. Surprise, birds have ear lobes more

(01:27):
often than not. Chickens with white or lighter ear lobes
tend to have white feathers and thus white eggs, while
those with colored feathers and ear lobes tend to produce
colored eggs. Where does this color come from? Though, Here's
where Understanding how an egg comes to be is important.
Chicken yolks or ova form in the chickens ovaries. A
fully formed ovum will leave the ovary and be deposited

(01:50):
into the oviduct. This part of the chicken's reproductive system
has five distinct sequential segments which the yolk passes through
on its way to the outside world. But it's the
fourth one, the shell gland, that affects the color of
the egg. This is where the shell forms around the ovum.
Fowler explained the process. He said, the shell of all
chicken eggs are made of calcium carbonate, a crystal that's

(02:13):
white in color. So all eggs are at least at
the start white. Any that we then see that our
other colors have had a pigment deposited on them as
they were moving through the overduct, after the white egg
shell had been deposited. You can see this if you
open up a brown egg and look at the inside
of the shell, it'll be white. Two pigments are responsible
for the spectrum of chicken egg color. Shades of greens

(02:35):
and blues are caused by the pigment bill of vert in,
while protoporphyrin is responsible for reddish brown hues. The same
egg coloring process holds true for all birds with colorful eggs.
American robin eggs, for instance, are famously blue. Oh but
that egg inside an egg story that you might have
seen going around the internet, that's another thing entirely, and

(02:56):
involves an egg accidentally reversing its course in the oviduct. Meanwhile,
we'll leave you with the answer to a practical egg query.
Should chicken eggs be kept refrigerated or at room temperature.
It depends on whether you live in a country Australia, Japan,
and the United States, for instance, that requires eggs produced
for commercial sale to be washed. This protects against salmonella,

(03:18):
but also removes a waxy shell coating that naturally defends
eggs against micro organisms, thereby necessitating refrigeration. Today's episode was
written by Christopher Hassiotis and produced by Tristan McNeil and
Tyler Clang. For more on this and lots of other
foul topics, visit our home planet, how stuff Works dot com.