
What you see: Some dark brown spots on your light brown egg. They don’t look like dirt or manure, but don’t look quite right either. They may or may not be raised.
What it is: A poor paint job by the chicken. Maybe also some calcium carbonate deposits.
Eat or toss: The egg inside is fine!
An egg with dark spots and/or bumps on its shell is still OK to eat
Here’s a fun fact: all chicken eggs start out with white shells. The chicken “paints” them various colors after forming the shell in what’s literally called her shell gland.
When you see dark brown spots on an otherwise lighter brown egg, it’s simply a case of an uneven paint job. Deana R. Jones, director of the U.S. National Poultry Research Center, likened egg production in the chicken to a car assembly line, where, sometimes, something goes awry.
“She apparently had a ‘clogged nozzle’ and didn’t do a continuous coat,” Jones said. “It’s just pigment, it has absolutely nothing to do with the quality or safety of the egg.”
In the image featured at the top of this post, you might also notice that the eggshell has some bumps, those are clumps of calcium carbonate (the same stuff that makes up the egg), which are also harmless (more on bumpy shelled eggs here). Look closely and you’ll also see what looks like white powder around the dark spots. That’s actually parts of the white eggshell that just didn’t get a proper paint job. Imagine if, for some reason, you were using a large paintbrush to coat a sidewalk with paint, but the sidewalk had a rock on it. Your paintbrush might miss some areas around the rock, right? So, what looks like a white powder is actually just parts of the egg that didn’t get their complete pigment application, possibly due to some roughness on the surface.
More cool facts about chicken egg color
Because the color is applied later in the process, brown eggs are white on the inside (if you haven’t noticed this before, you surely will next time you crack open a brown egg).
The egg-making process takes about 26 hours, with the shell construction lasting about 20 hours. Colors are added during the last five hours.
Blue chicken eggs, which aren’t typically sold in stores, are “painted” earlier in the process and the pigment more often penetrates, making them blue on the inside as well as the outside. From backyard chickens or farmers market vendors, you might also see “olive” eggs, which are a mix of blue- and brown-egg-producing breeds.
SOURCES:
- Deana R. Jones. Center Director, U.S. National Poultry Research Center. U.S. Department of Agriculture, Agricultural Research Service. Video call October 2024.
- How Do Chickens Lay Eggs? Understanding Your Egg-Laying Chickens. Patrick Biggs, Ph.D. Purina Mills. Accessed November 2024.
- Why are chicken eggs different colors? Dorothy Munn, Michigan State University Extension. Michigan State University. December 29, 2013