Think about it.
Why did people use to leave their eggs on the kitchen counter for weeks when today, if you don’t keep your eggs in the fridge, they rot overnight?
The bloom, friends. The bloom.
As an egg leaves a hen’s body, it is coated with a thin membrane called a bloom (aka cuticle). The bloom seals the tiny holes in the egg’s shell and keeps it sterile. As long as the bloom is intact, eggs can stay out in the open for weeks and weeks.
Evolution. When a chicken decides to go “broody” (when she wants to hatch babies), she starts collecting eggs into a “clutch.” When she gets about 14 eggs, she sets them.
The average hen lays about 5 eggs per week. So, it takes roughly three weeks to gather her clutch. That means the first egg she lays has to sit outside (and sometimes in extreme heat) for that long without spoiling. Nature created the bloom to keep eggs viable until Momma Hen sets her clutch.
That’s how your great-granny was able to keep eggs un-refrigerated for so long. Most folks back then collected their own yard eggs so the bloom was intact.
Can I leave my store-bought eggs on the counter?
Nuh-uh. The key to an intact bloom is to not wash the egg, and that is the first thing commercial egg producers do. Washed egg = no bloom = has to be refrigerated.
The same applies to backyard chicken eggs. If you wash them, they will spoil. If you keep chickens and want to leave your eggs out, just take them out of the nest box and leave them be. This grosses some folks out. If you are one of them, wash your yard eggs and put them in the fridge.
One last tip.
If your yard eggs have a little poop or crud on them from the nest box, use a DRY cloth to gently brush it away, then put in your egg basket. And relax, we’ve been doing it for 15 years. Just wash all eggs right before using.