Eggs are a healthful source of protein and other essential nutrients. Although properly stored eggs have a decent shelf life, they can eventually spoil. However, there are several simple ways in which a person can check whether an egg is still good to eat.
In this article, we look at some straightforward ways to tell whether an egg is safe to eat. We also discuss how long eggs stay fresh, whether to refrigerate them, and the health risks of eating a bad egg.
One of the simplest and most reliable ways to tell whether an egg has gone bad is to smell it.
A bad egg will give off a foul odor when a person cracks the shell open. This smell will be present even if the person has already cooked the egg.
In some cases, when an egg is very old or rotten, a person can smell the foul odor before cracking it open.
People should throw out any eggs that give off a foul or unpleasant odor. As this test is very reliable, it is a good idea to smell every egg before using it.
Sometimes an egg will look or feel off. A person should check for signs of possible contamination or rottenness.
People should discard eggs with any of the following characteristics:
- cracks in the shell
- a powdery substance on the shell
- a shell that looks or feels slimy
Eggs with cracked or slimy shells may have become contaminated with bacteria, while a powdery substance on the shell can be a sign of mold.
If the shell is intact with no obvious signs of damage or contamination, and it does not smell, a person should do a second visual check after cracking the egg open. They should discard eggs with any unusual discoloration inside, such as pink, iridescent, or greenish egg white or yolk.
However, eggs that develop a green ring on the hard-cooked yolk after cooking are safe to eat, according to the United States Department of Agriculture (USDA). The green color is often the result of overcooking or high iron content in the cooking water.
An egg white or yolk that is runnier than usual can also indicate that an egg is past its prime. While this does not necessarily mean that the egg is unsafe to eat, it can affect the egg’s taste and cooking properties.
Before purchasing eggs, a person should do a quick visual examination of the eggs in the carton. If any eggs are cracked or leaking, choose a different pack.
People who keep eggs in their original carton can also check for an expiration date to see whether the eggs are still good. However, the information on the carton can sometimes be a little confusing.
In the U.S., the Food Safety and Inspection Service do not require producers to print the expiration or sell by date on egg cartons.
According to the USDA, if an egg producer does choose to include an expiration date, it must be in month/day format and follow an appropriate prefix, such as “Exp.,” “Sell by,” and “Not to be sold after the date at the end of the carton.”
However, producers must include the “pack date” on all cartons of USDA graded eggs.
A pack date is a three digit number representing the day of the year when the producer washed, graded, and packed the eggs. For example, a pack date of 001 is January 1, and a pack date of 365 is December 31.
If a producer of USDA graded eggs does choose to include an expiration date, it must be no more than 30 days after the pack date.
The float test is a quick and easy way to check the freshness of an egg. The float test does not determine whether an egg has gone bad, but it does provide a useful indication of the age of an egg.
To perform the float test, place the egg in a large bowl of water. If the egg sinks or stays at the bottom, it is still fresh. An older egg will either stand on its end or float.
The float test works because air builds up inside the egg as it ages, and this increases its buoyancy.
However, an egg that floats may still be safe to eat. A person can further test the egg by cracking it open to smell it and check it for visible signs of contamination.
Candling is a technique that producers use to inspect the quality of an egg. It involves using a bright light to examine eggs for signs of cracking and interior defects.
Egg producers generally use automated conveyor belts and mechanical sensors to check large numbers of eggs quickly and efficiently. However, a person can also perform candling at home by holding an egg up to a bright light, such as a powerful torch or lamp, in a darkened room.
As with the float test, candling only checks the freshness of the egg. It will not confirm whether the egg is still safe to eat.
When they hold the egg up to the light, a person should be able to see the air cell inside it. The air cell is a small sac or bubble that is usually present in the larger end of the egg.
The egg is still fresh if the cell is less than one-eighth of an inch deep. The larger the air sac, the older the egg.
According to the USDA, refrigerated eggs stay fresh for 3 to 5 weeks after the pack date on the carton. However, displaying the pack date is only necessary for USDA graded eggs.
The USDA recommend refrigerating eggs as soon as possible to maintain freshness and reduce the risk of Salmonella contamination.
The USDA also warn that people should not leave refrigerated eggs out at room temperature for more than 2 hours. Cold eggs can sweat as they warm up, which can increase the risk of bacterial growth.
The main risk of eating bad eggs is Salmonella infection, which is a form of food poisoning. Salmonella is a type of bacteria that can grow both on the shell and inside the yolk and egg white.
Symptoms of Salmonella infection can include:
According to the Centers for Disease Control and Prevention (CDC), symptoms usually develop 6–48 hours after eating a contaminated egg and last for about 4–7 days.
Most people recover from Salmonella infection without antibiotics. However, people with severe symptoms may require hospitalization.
Salmonella infection is often more severe and dangerous in certain groups of people, including:
- adults over the age of 65 years
- children younger than 5 years
- people with weakened immune systems, such as those who have undergone an organ transplant or are living with HIV
Not everyone who eats a bad egg will develop Salmonella infection.
Steps that a person can take to reduce the risk of Salmonella include:
- washing the hands and any objects that come into contact with raw eggs
- keeping eggs refrigerated
- discarding eggs after the expiration date
- cooking eggs thoroughly so that both the yolk and white are firm
- using pasteurized eggs for dishes that require raw or lightly cooked eggs
When eggs spoil, they begin to smell bad, and the yolk and egg white may become discolored. Cracked or slimy eggshells can also be a sign of bacterial contamination.
Easy ways to determine an egg’s freshness include checking the expiration date, visually inspecting the eggshell, and cracking the egg open to smell the inside. If a person has any doubt about whether an egg has gone bad, they should throw it out.
The main risk of eating bad eggs is Salmonella infection, which can cause diarrhea, vomiting, and fever. A person can reduce the risk of Salmonella by keeping eggs refrigerated, discarding eggs with cracked shells, and cooking eggs thoroughly before eating them.