Fill a bowl with water and drop the egg in.
Lies flat on the bottom — fresh. Sinks but stands upright on its fat end — older, still fine, use it this week. Floats — do not crack it into anything you would miss.
We are, essentially, running a witch trial. The difference is that ours measures something real.
What the bowl is actually telling you
An eggshell has around seven thousand pores and it breathes through every one of them. Water vapor leaves through those pores each day of an egg's life and never comes back. That is what aging means for an egg. It does not spoil so much as it slowly dries out.
There is a pocket of air at the fat end. As water leaves, that pocket grows. A fresh egg is dense and lies flat. An older egg has traded water for air, gotten lighter, and starts to tip up. Enough air and it floats.
The float test is a dehydration test. It measures how much the egg has breathed. Nothing more.
A floater is usually just old. Old eggs also peel beautifully after hard boiling, which is why people who make deviled eggs buy them early on purpose.
Since warmth speeds that water loss, an egg on the counter ages faster than an egg in the fridge. Same egg, different clock. That is the whole case for refrigeration.
One thing outranks the bowl: crack it into a separate dish first. A genuinely bad egg tells you immediately, and nobody has ever needed a second opinion. The float test is for eggs you are unsure about. Your nose is for eggs you are genuinely concerned about.
How long are eggs good after the expiration date?
South Carolina law requires a carton display either the day the eggs were PACKED or an expiration date, and that expiration may not exceed 45 days from packing. That is the whole rule. Whichever date is on your carton, the clock behind it starts the day those eggs went into the box.
Which raises the question nobody asks standing at the shelf. When did the hen lay the egg? And then how long until it was packed?
Packed is not laid
Under the federal grading rules, an egg can be up to 21 days old on the day it is packed and still carry the USDA shield. Three weeks in a cooler before the date on your carton even begins.
South Carolina asks producers to grade and pack within a reasonable period of time from gathering. It does not say how long that is.
Work backward from the best-by date and a grocery store egg can be up to 66 days old. 45 back to the pack date and another 21 before that.
That is not a scandal. It is how a national supply chain moves eggs from a barn in one state to a grocery store shelf in another. But it is a range, not a number, and the carton will never narrow it down more than that for you.
A food safety specialist at Ohio State put it plainly to Consumer Reports: eggs are generally good four to six weeks after they are laid, but we do not know when that was, so we lean on the printed date.
European cartons work the other way. Their date counts from laying, and their best-before is capped at 28 days. Shorter window, earlier start. There are reasons for that difference and they have almost nothing to do with the egg — we get into it here.
Our eggs are gathered by hand twice a day and packed the same week they are laid. There is no three week window here. Order for Pickup on Thursday or Saturday, or have Farmer David deliver to you.
Why we walk the field twice a day
We gather by hand, morning and afternoon. Not because it is quaint. Because every hour an egg sits in a nest box is an hour it spends breathing.
Anything on the ground is set aside for the pigs. An egg laid in the dirt has been in contact with everything in that dirt, for however long we cannot be certain. There is no version of that worth a dollar.
The reason for that rule is worth seeing once, from a distance.
When a rogue hen goes broody somewhere she should not and tries to hatch out a clutch of unfertilized eggs — we do not keep any roosters on our farm — she will eventually abandon her nest and leave the time bombs behind. In an egg that is genuinely going bad, pressure from decomposition builds in the shell until the shell cannot hold it any longer.
They explode. And with a smell that ends the conversation.
That is real decomposition, a different animal from the slow evaporation your float test measures. But it is the same shell and the same pores. An egg trades slowly with the world around it. How it is handled decides how that trade goes, which is why we are particularly careful with all of ours.
Short version
Buy well ahead of the best-by date. Bowl of water when you are unsure. Nose when you are worried. Cold and steady at home.
And if you want to know when your eggs were laid rather than when somebody put them in a box, that is a question you can only ask a farmer.
