Protein
The outer compact layer of the cuticle is mostly protein and glycoprotein, plus roughly 4 to 5 percent carbohydrate and 3 percent lipid.
The bloom
There is a coating on your eggs. Here is what it does.
Our eggs are never washed, which means they still have the thin natural layer the hen puts on the shell on her way out. It is called the cuticle, or the bloom. It is the whole reason “nest run” is a different thing from a carton off the shelf — and it is worth understanding before you put it in your refrigerator.
The short version
- The bloom is a protein coating a few thousandths of a millimeter thick.
- It plugs the thousands of microscopic pores in the shell.
- Washing removes it. We do not wash, so ours still have it.
- It is not a substitute for a refrigerator. We recommend refrigerating your eggs as soon as they arrive, and cooking them thoroughly.
Inside the shell
Seven layers, and the outermost one is the fragile one.
An egg is not a container with something in it. It is a stack of layers, each doing a job, built in about twenty-four hours. The bloom is the last thing added and the first thing lost.
Scroll sideways to see the whole diagram
What it actually is
Wet when it is laid, dry within a few hours.
The cuticle goes on last, in the final minutes before the egg is laid, and it goes on as a thick viscous liquid. It does not finish setting up for about six hours afterward. That is why a just-laid egg feels faintly tacky and an egg from that morning does not.
Once dry it is two layers: an inner one studded with tiny mineral vesicles, and an outer compact layer that is about 85 to 90 percent protein and glycoprotein, with a little carbohydrate and a little lipid. It is essentially a protein varnish.
And it is not inert. Researchers have identified a specific set of antimicrobial proteins sitting in it — lysozyme, ovotransferrin, ovocalyxin-32, ovocalyxin-36, ovocleidin-17, ovalbumin, cystatin. Several of those are the same proteins that make egg white itself hostile to bacteria.
Sources for this section: the Frontiers in Immunology review of the eggshell cuticle and ScienceDirect's overview of egg composition.
To set
The cuticle is laid down as a liquid and does not fully mature for about six hours after the egg is laid. Handle a warm egg gently.
The part people find surprising
A shell is not solid. It has thousands of holes in it.
A single eggshell has somewhere between seven thousand and seventeen thousand pores in it, with roughly twice as many crowded at the blunt end. They have to be there — an embryo needs to breathe. But a hole that lets air out also lets things in, which is what the cuticle is for.
Scroll sideways to see the whole diagram
Two continents, two answers
America washes its eggs. Europe is not allowed to.
Wash, then refrigerate
Commercial US eggs are washed and sanitized before they are graded and packed. Washing takes the cuticle with it, so refrigeration is not optional afterward — it is the thing doing the protecting. Canada, Australia and Japan work the same way.
Do not wash at all
EU rules prohibit commercial washing of Class A table eggs specifically to keep the cuticle intact, which is why supermarket eggs in Europe sit unrefrigerated on a shelf. Roughly 95 percent of table eggs in China are unwashed as well.
Ours are in a third category, and Arizona has a name for it: nest run. Unwashed and ungraded, sold as-is, not sorted by size or grade. We are not permitted to wash or grade them, and we would not want to — but that also means the state has not inspected or graded them, and you should know that going in.
Background: ANSI on the US and European approaches and the Iowa State Center for Food Security and Public Health.
The honest part
So do you have to refrigerate them? Legally, no. We are going to tell you to anyway.
This is the question we get most, and there is a version of the answer that would sell more eggs. We would rather give you the real one.
You will read all over the internet that the bloom seals the egg and makes the refrigerator unnecessary. The people who study eggs for a living are more skeptical than that. A researcher at the USDA's Agricultural Research Service put it plainly: the cuticle dries and comes off, and from an evolutionary standpoint it is not there to keep Salmonella out of the egg — it is there to control respiration during incubation.
And then there is the quality question, which is not close. In a fifteen-week ARS study running 5,400 eggs a week, unwashed eggs held at 72°F dropped from Grade AA to Grade B in a single week and lost about 15 percent of their weight to evaporation over the run. Eggs that were refrigerated at 39°F were still Grade A fifteen weeks later. The same group found that yolk quality can decline more sitting on the counter for under a day than it does across fifteen weeks in a refrigerator.
Their summary is one sentence long: regardless of washing status, refrigeration is key.
Where the bloom clearly does help is when a refrigerator is not an option. In a 2023 study, unwashed eggs held usable quality for 24 days at 86°F and 18 days at 95°F — about three times and two times as long as washed eggs at the same temperatures. That is a real advantage. It is just not an argument for leaving them out when you have a refrigerator ten feet away.
So: we recommend refrigerating your eggs as soon as they arrive, keeping them in the carton, and cooking them thoroughly. If you choose to keep them on the counter instead, you are not doing anything unusual by world standards — but you will lose quality quickly, and that is your call to make with the information in front of you.
Sources: USDA ARS, “How We Store Our Eggs — and Why”, the ARS egg storage summary, and a 2023 study in Food Science of Animal Resources.
How long they keep
Same egg. Two very different clocks.
An unwashed egg on the counter and the same egg in the refrigerator are not on remotely the same schedule. Neither number is a hard expiry — they are quality curves.
Scroll sideways to see the whole diagram
Do not wash them until you cook them
Leave the bloom on until the last possible second. Rinse each egg under warm running water right before you crack it — warm, not cold, because cold water can draw surface moisture inward through those pores.
Keep them in the carton
The carton slows evaporation and keeps eggs from picking up refrigerator smells through the shell. Pointed end down keeps the yolk centered and the air cell where it belongs.
The float test still works
Drop an egg in a glass of water. Lies flat on the bottom, it is at its best. Tilts up, it is older but fine. Floats, the air cell has grown large enough that we would not use it — throw it out.
One more thing, and it is a favor to us: we always appreciate getting egg cartons back. Leave your empties out on delivery day and they go straight back into rotation.
Unwashed, ungraded, and honest about it.
NEST RUN EGGS. Prescott, Prescott Valley, Chino Valley and Dewey.
From $12 a dozen · delivery included