How To Tell If Eggs Are Bad

What does a bad egg look like?

How To Tell If Eggs Are Bad

Reading Time: 6 minutes

If you’ve ever wondered how to tell if eggs are bad or not, you’re not alone. The internet is awash with tips, tricks, and partially informed answers that may or may not be correct. Today I hope to clarify a few things. Firstly, let’s define what I’ll be calling a “bad egg.” I’ll then explain the biology behind what makes eggs go bad, How to tell if eggs are good, and finally, we’ll cover the basics of safe egg handling.

What Is a “Bad Egg?”

For the sake of this article, a “bad egg” is an egg that is inedible or unsafe to eat, such as a rotten egg. Additionally, the FDA and USDA both recommend that all eggs showing cracked shells or visibly dirty shells should be considered a “bad egg,” and we’ll discuss why.

All About The Shell

Eggshells are a porous structure by design. This porous surface allows things such as air, moisture, and some contaminants to pass through. When laid, the hen also deposits a thin protective film over the shell known as the cuticle or bloom, which serves as a natural protective barrier. This cuticle is not completely impenetrable, so regardless of if you wash away the cuticle layer or not, things will traverse that porous shell eventually.

Just because an egg floats doesn’t mean it’s gone foul. It might mean it’s old and dehydrated, but there are situations where a fresh egg can float. Likewise, an egg that sank could be perfectly good, gone rotten, or even have a developing embryo.

What Makes Eggs Go Bad?

Spoilage bacteria are the most common culprits of eggs turning rotten. Once these bacteria, which are common in the coop environment, manage to traverse the shell and enter the egg, they begin to multiply. These organisms cause the insides of the shell to spoil and rot.

Shell Integrity

Contaminants find it far easier to enter the egg if the shell is compromised, such as a crack, which is why the USDA and FDA consider cracked eggs a no-go. Additionally, visibly soiled eggs are likely to have an excessive bacterial load, so it’s best to discard them as well. The USDA and FDA are more concerned with Salmonella, but regardless, dirty or broken eggs should be tossed.

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Once cracked, this day-old egg’s yolk and albumin sit tall and proud. The spread of albumin is also very limited and close to the yolk; all hallmarks of a fresh egg.

Oxidation

Absent of spoilage bacteria, an egg can still deteriorate through oxidation all on its own. Oxidation is a chemical process that occurs when oxygen contacts fats and proteins and causes them to break down. The result of this process is evident when you crack an egg open and compare an older egg to a fresh egg. The older egg that has deteriorated will have albumin and yolk that does not sit as tall in the pan as the fresh example. Additionally, you’ll likely see that the older egg spreads out farther and may not retain its shape well. Reduction in interior quality does not mean the egg is inedible, but it is evidence of the natural process of decay. The good news is this; when eggs are appropriately washed and stored in a refrigerator, they are more likely to dehydrate before they turn rancid from oxidation alone.

How to Tell if Eggs Are Bad

Candling is an excellent bad egg test we can do at home. Using an egg candling tool or a powerful flashlight, illuminate your eggs and observe its contents. If the egg albumin appears translucent and you can see an egg yolk, things are looking good. The presence of branch-like structures indicates you likely have a partially incubated egg. If you can’t see any defined shapes, it appears solid, or all you can see is an air cell, discard that egg because it’s likely gone bad. Likewise, if cracks in the shell are visible when candling, trash it. Candling suspicious eggs is an excellent test because it can help you avoid opening an unpleasant surprise in the kitchen.

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Candling is a skill, and it’ll take a little trial, error, and practice. A strong flashlight and a dark place are all you need to take a peek inside.

How to Tell if Eggs Are Bad after Cracking

If your candling looked promising, crack your eggs and take a look. Is there anything out of the ordinary? Is there an odor? Do they smell off? If it looks good and smells good, you’re in business, but if there’s anything that makes you second guess your eggs, ditch them. Sometimes a fresh-cracked egg will have a green tinge to them. A green hue in a raw egg is indicative of a higher than average concentration of riboflavin (vitamin B2). Although it looks odd, it’s safe to eat.

The Egg Water Test

Many people misinterpret the classic egg freshness test or “float test.” The float test is what it sounds like; you place eggs in water and see if they float or sink. Proponents of the float test say that eggs that float are old, and those that sink are fresh, but that may not be true.

Buoyancy

What is true of the float test is this; If the egg sinks, it weighs more than the amount of water it displaces. If it floats, it weighs less than the volume of water it displaces. In that regard, the float test is incredibly accurate. This is an extremely distilled explanation of Archimedes’ Principle.

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This commercial egg has been cracked a full 30 days past the “use by” date. Note the significant difference in albumin height and spread. Despite this, this egg is still good. 

Interpretation

Where people go wrong with the float test is this: they misinterpret its results. Just because an egg floats doesn’t mean it’s gone foul. With your average-sized egg, it might mean it’s old and dehydrated, but there are situations where a fresh egg can float. Likewise, an egg that sank could be perfectly good, gone rotten, or even has a developing embryo. In short, the results of this test do not directly correlate with a “good” or “bad” verdict and should not be relied upon in that manner.

Reduction in interior quality does not mean the egg is inedible, but it is evidence of the natural process of decay. The good news is this: when eggs are appropriately washed and stored in a refrigerator, they are more likely to dehydrate before they turn rancid from oxidation alone.

Egg Safety

Just because an egg passes muster doesn’t mean they’re guaranteed safe to eat raw. It’s always best practice to thoroughly cook eggs to kill any potential bacteria present. The FDA has an excellent advisory page on egg safety; I encourage everyone to read. 

Keeping Eggs Fresh

Many people engage in the “to refrigerate or not” debate when it comes to shell eggs. Refrigeration does several things for us; it retards bacterial growth, fungal growth, and internal oxidation. I prefer to follow the FDA’s egg rule, which says that eggs must be refrigerated at or below 45℉ within 36 hours of being laid. The FDA’s chief concern is to reduce the likelihood of Salmonella poisoning. Still, proper refrigeration minimizes the potential of an egg going rotten and preserves its interior quality.

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This commercial egg was cracked a full 30 days past the “use by” date. Note the spread and more watery appearance of the albumin. Notable as the age is, it’s still good.

How Long Can They Go?

If you’ve ever wondered, “Do eggs expire?” The answer technically is yes, but that expiration date found on commercial cartons is the date at which retailers can’t sell them anymore. USDA regulations on egg carton labels stipulate several things. “Sell by” dates can not exceed 30 days from packaging date, and “use by” dates are not to exceed 45 days from packaging. After 45 days, the USDA says the interior quality of the eggs begins to diminish. It doesn’t mean they’ve gone rancid, it merely means their internal quality has started to degrade.

The Take-Away

I always advise you to refrigerate clean eggs in clean cartons for the best results. Candling can tell you nearly everything you need to know about what’s going on inside your eggs. Don’t rely on the float test to tell you if your eggs are good or bad, and lastly, trust your nose. If the egg you cracked smells bad, then it is.

How often do you find a bad egg at home? Let us know in the comments below!

Originally published in the June/July 2020 issue of Backyard Poultry and regularly vetted for accuracy.

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