How to Test if an Egg is Good: Ancient Kitchen Wisdom Meets Modern Science

Somewhere between the refrigerator door and your morning omelet lies a moment of uncertainty that has plagued home cooks since humans first raided bird nests. That pristine white shell reveals nothing of its contents, leaving you to wonder whether you're about to crack open breakfast perfection or unleash an olfactory nightmare that'll have you opening windows in January.

I've been there myself, standing in my kitchen at 6 AM, holding an egg like Hamlet contemplating Yorick's skull. The carton says it expired three days ago, but we all know those dates are more suggestion than scripture. What follows is everything I've learned about egg testing through years of cooking, some unfortunate experiences, and conversations with everyone from backyard chicken keepers to food scientists who get genuinely excited about protein denaturation.

The Float Test: Your First Line of Defense

Fill a bowl with cold water deep enough to submerge an egg completely. Gently lower your suspect egg into the water and watch what happens. A fresh egg will sink and lie flat on its side at the bottom. An egg that's a week or two old might stand on one end but still touch the bottom. If it floats? That's nature's way of telling you this egg has seen better days.

The science behind this is beautifully simple. Eggshells are porous – about 17,000 tiny pores, if you're counting. As an egg ages, moisture evaporates through these pores and air seeps in, creating an ever-expanding air cell at the blunt end. Eventually, this air pocket becomes large enough to make the egg buoyant. It's like a built-in expiration indicator that requires nothing more than a bowl of water.

But here's where it gets interesting – a floating egg isn't necessarily bad, just old. I've used plenty of floaters for hard-boiling (they're actually easier to peel). The real question is what you plan to do with that egg. For meringues or mayonnaise where freshness matters? Skip the floater. For a well-cooked scramble? You're probably fine.

The Candling Method: Seeing Through the Mystery

Before electric lights, our ancestors held eggs up to candle flames to peer inside – hence the term "candling." Today, you can use a flashlight or your phone's torch function. In a dark room, hold the light source against the larger end of the egg and tilt it slightly.

Fresh eggs show a small air cell (about 1/8 inch deep) and a barely visible yolk. As eggs age, that air cell grows, and you might see the yolk moving more freely when you rotate the egg. If you spot dark patches or can't see through the egg at all, that's your cue to move on.

Professional egg graders still use this technique, though with fancier equipment. I learned this from a farmer at my local market who candled every egg before selling. She could spot a double yolk or a fertilized egg with just a quick glance – skills that come from examining thousands of eggs over decades.

The Shake Test: Quick but Controversial

Hold the egg close to your ear and give it a gentle shake. A fresh egg should be silent – the thick albumen (egg white) holds everything in place. An older egg might produce a sloshing sound as the thinned whites allow the yolk to move around.

Now, I'll be honest – this method divides the cooking community. Some swear by it, others claim it's about as reliable as a weather forecast. In my experience, by the time you can hear sloshing, that egg is well past its prime for most uses. It's a decent backup test, but I wouldn't stake my soufflé on it alone.

The Crack and Inspect Method: The Final Verdict

Sometimes you just have to commit. Crack the egg onto a flat plate (not into your mixing bowl – learned that one the hard way). A fresh egg will have a firm, rounded yolk that sits high, surrounded by thick white that stays close to the yolk, with a thinner outer layer. The older the egg, the flatter and more spread out everything becomes.

Look for these warning signs:

Pink or iridescent egg whites (bacterial growth)
Green or black spots (mold)
Any off-putting smell beyond the neutral, slightly eggy scent
Watery consistency throughout with no distinction between thick and thin whites

That sulfur smell everyone talks about? If you detect even a hint of it, don't try to be a hero. No recipe is worth that risk.

Understanding Egg Dating: A Numbers Game

Those dates stamped on egg cartons can be cryptic. The sell-by date is usually 30 days from packing, but eggs can last 3-5 weeks beyond that if properly stored. Some cartons show a three-digit Julian date – that's the day of the year the eggs were packed (001 for January 1st, 365 for December 31st).

Here's something most people don't realize: commercial eggs in the U.S. are washed and sanitized, removing the natural protective coating called the bloom. This is why Americans refrigerate eggs while many other countries don't. That washing process actually makes our eggs more vulnerable to contamination and quicker to spoil once the shell is compromised.

Storage Matters More Than You Think

Keep eggs in their original carton in the main body of your refrigerator, not in those cute little egg holders in the door. The door is the warmest part of your fridge with the most temperature fluctuation – exactly what you don't want for egg storage. The carton prevents the eggs from absorbing odors (remember those 17,000 pores?) and helps maintain humidity.

Store eggs with the pointed end down. This keeps the air cell at the top and the yolk centered – particularly important if you're planning to hard-boil them or want picture-perfect fried eggs.

Special Circumstances and Considerations

Farm-fresh eggs with intact bloom can sit on your counter for a couple of weeks, though refrigeration still extends their life. Once washed, though, they need refrigeration just like store-bought eggs.

Cracked eggs should be used immediately or discarded. That shell is your primary defense against bacteria, and once breached, all bets are off. I've seen people try to save a slightly cracked egg for "just one more day" – it never ends well.

For separated eggs, whites can last 2-4 days in the fridge, yolks only 1-2 days (cover them with water to prevent drying). Both freeze well for longer storage, though frozen yolks need a pinch of salt or sugar to prevent them from becoming gelatinous.

When Good Eggs Go Bad: A Personal Cautionary Tale

Let me paint you a picture. It's Thanksgiving morning, I'm making my grandmother's famous angel food cake, and I need twelve egg whites. Eleven eggs in, feeling confident, I crack number twelve directly into the bowl. The smell hit me like a physical force – sulfur mixed with something indescribably wrong. That one bad egg ruined the entire batch, and there wasn't time to start over.

Since then, I always crack eggs individually into a small bowl first, especially when working with multiple eggs. It takes an extra minute but saves potential disaster. Call it paranoid if you want, but anyone who's experienced a truly rotten egg never forgets it.

The Bottom Line on Egg Testing

Perfect freshness matters most for poaching, frying sunny-side up, making meringues, or any preparation where the egg's structure is crucial. Week-old eggs work fine for scrambling, baking, or hard-boiling. In fact, slightly older eggs are preferred for hard-boiling because they peel more easily.

Trust your senses, use multiple testing methods when in doubt, and remember that "best by" dates are quality indicators, not safety deadlines. With proper storage and these testing techniques, you can confidently use eggs well beyond their printed dates while avoiding any unpleasant surprises.

The real skill isn't just knowing how to test an egg – it's understanding what level of freshness your recipe actually requires. Master that, and you'll waste fewer eggs while still maintaining the quality your cooking deserves.

Authoritative Sources:

United States Department of Agriculture. "Shell Eggs from Farm to Table." USDA Food Safety and Inspection Service, www.fsis.usda.gov/food-safety/safe-food-handling-and-preparation/eggs/shell-eggs-farm-table.

Ricke, Steven C., et al. Achieving Sustainable Production of Eggs Volume 1: Safety and Quality. Burleigh Dodds Science Publishing, 2017.

McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen. Scribner, 2004.

Stadelman, William J., and Owen J. Cotterill, editors. Egg Science and Technology. 4th ed., CRC Press, 1995.