October 2022

A lack of knowledge about how to tell when an egg has gone bad leads some people to needlessly throw away good eggs. You can avoid that by using simple tests to determine if your egg is good or bad.

First, a bit of background.

Over time, an egg’s quality begins to decline. That’s because of the egg’s unique structure:  

Eggs come in two parts: the outer shell – thin, fragile and a lot more porous than you’d expect. In fact, it has thousands of microscopic holes that allow it to “breathe”. The other part – the egg’s “innards” is comprised of the white and the yolk.

A thin membrane that attaches the “innards” to the outer shell.  As the eggs ages, the membrane begins to shrink and detach, creating an air pocket between it and the shell. Eventually, bacteria or mold seep through the shell and into the air pocket, and the egg “goes bad” and starts to decompose.

But if you keep your eggs refrigerated, they will be perfectly good to eat for many weeks. Refrigeration prevents bacterial growth and preserves quality and taste.  It also expands eggs’ uses: older eggs are easier to boil and peel because the membrane has pulled loose from the shell and can be picked off with ease.

The tests

When in doubt, there are several methods you can use to determine if eggs are safe to eat. Here are the top four tips to tell if your eggs are good or bad.

1. Check the dates

One of the easiest ways to tell if your eggs are still good is to check the three dates printed on the carton.

In the United States, eggs may be labeled with either a “sell by” or expiration date, depending on which state you live in, in order to let you know if your eggs are still fresh.

A “sell by” date indicates how long a store should offer eggs for sale — no more than 30 days after packing — but not necessarily that the eggs have gone bad.

An expiration date, on the other hand, marks the date after which the eggs are considered less than fresh.

If neither of these labels is present, there is yet another date you can look for to tell how fresh your eggs are.

Eggs that have been graded by the USDA are required to show the “pack date” on the carton, which is the day that the eggs were graded, washed, and packaged. But you may not recognize it if you don’t know what to look for.

The “pack date” is printed as a Julian date, meaning each day of the year is represented by a corresponding, chronological number. Therefore, January 1st is written as 001 and December 31st as 365.

If your eggs are still within the expiration or “sell by” date on the carton, or within 21–30 days after the “pack date,” you can be pretty sure they are still fresh.

2. Conduct a sniff test

The sniff test is the oldest, simplest, and most reliable method of telling whether an egg has gone bad.

Eggs that have gone bad will give off an unmistakable smell, regardless of whether they are raw or cooked.

If you can’t already tell while the egg is in the shell, crack the egg onto a clean plate or bowl and give it a sniff.

If anything smells off, toss the egg and wash the bowl or plate with hot, soapy water before using again.

If things smell normal, meaning there is no odor at all, that’s a good sign that the egg is still safe to use.

3. Do a visual inspection

In addition to your nose, your eyes are a valuable tool for telling whether an egg is good or bad.

While the egg is still in its shell, check that the shell is not cracked, slimy, or powdery.

Sliminess or cracks can indicate the presence of bacteria, while a powdery appearance on the shell may indicate mold.

If the shell appears dry and undamaged, crack the egg into a clean, white bowl or plate before using. Look for any pink or iridescent discoloration in the yolk or whites, as this may indicate bacterial growth.

If you notice any signs of discoloration, throw the egg out and wash the bowl with hot, soapy water before testing a new egg.

You can also check to see if the whites or yolk of the egg are runny. This is an indication that the egg is old and that the quality has declined. But this does not necessarily mean it has gone bad, and it can still be perfectly fine to use.

4. Perform a float test

The float test is one of the most popular methods for checking whether an egg is good or bad.

This is also a common method for determining the age of a fertilized egg that is developing into a chick. It works just as well to judge whether an unfertilized table egg is fresh or not.

To perform the float test, gently set your egg into a bowl or bucket of water. If the egg sinks, it is fresh. If it tilts upwards or even floats, it is old.

This is because as an egg ages, the small air pocket inside has grown larger as water is released and replaced by air. If the air pocket becomes large enough, the egg may float.

While this method may tell you whether an egg is fresh or old, it doesn’t guarantee whether an egg is good or bad. An egg can sink and still be bad, while an egg that floats may still be fine to eat. So it’s smart to use another test method, as well.

The bottom line

A lack of knowledge about how to tell when an egg has gone bad leads some people to needlessly throw away good eggs.

Among the strategies listed here, cracking an egg open, giving it a sniff, and checking for discoloration is the most conclusive method of determining freshness.

Keep in mind, though, that eggs containing bacteria that cause food-borne illness, such as Salmonella, may look and smell completely normal.

So don’t forget that even if an egg passes these tests, it’s important to fully cook it to a safe temperature before you eat it. Never eat a raw egg!

From Healthline.com