Although properly stored eggs have a decent shelf life, they can eventually spoil. There are several ways to check if an egg is still good to eat, such as carrying out a float test or inspecting the shell.
Eggs are a good source of protein and other essential nutrients. In this article, we look at some straightforward ways to tell whether an egg is safe to eat or not. We also discuss how long they stay fresh, whether to refrigerate them, and the health risks of eating a bad egg.
The float test is a quick and easy way to check the freshness of an egg. While it does not determine whether an egg has gone bad, it provides a useful indication of the age of an egg.
To perform the float test, place the egg in a large bowl of water. If it 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, increasing its buoyancy.
However, an egg that floats may still be safe to eat, according to the United States Department of Agriculture (USDA). A person can further test the egg by cracking it open to smell and checking it for visible signs of contamination.
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, according to the USDA. This smell will be present even if someone has already cooked the egg.
In some cases, when an egg is very old or rotten, individuals 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, contamination, or foul odor, a person should do a second visual check after cracking the egg open. They should discard eggs with any unusual discoloration inside, such as a 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 USDA. The green color is often due to 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 it is unsafe to eat, it can affect its taste and cooking properties.
Before purchasing them, a person should do a quick visual examination of the eggs in the carton. If any are cracked or leaking, choose a different pack.
People who keep eggs in the original carton can also check for an expiration date to see whether they are still safe to eat. However, the information on the carton can sometimes be a little confusing.
According to the USDA, the United States federal government does not require producers to print the expiration or sell-by date on egg cartons. However, some states require this information.
If an egg producer chooses 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 chooses to include an expiration date, it must be no more than 30 days after the pack date.
People can keep eggs in the refrigerator for 3–5 weeks. Even though the sell-by date may expire during that time, they may still be safe to eat. To keep them safe, a person should place them inside the refrigerator immediately after purchase. The refrigerator temperature should be 40°F (4°C), and people should place eggs in the coldest spot of the refrigerator rather than in the door.
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 flashlight or lamp, in a darkened room.
As with the float test, candling only checks the freshness of the egg. It will not confirm whether it 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.
According to the University of Florida Institute of Food and Agricultural Sciences, 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 3–5 weeks after the pack date on the carton. However, displaying the pack date is only necessary for USDA-graded eggs.
The USDA recommends refrigerating eggs as soon as possible to maintain freshness and reduce the risk of Salmonella contamination.
If a person eats raw eggs, they are at risk of a Salmonella infection, a form of food poisoning. Salmonella is a type of bacterium that can grow both on the shell and inside the yolk and egg white.
Symptoms of Salmonella infection can
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Most people recover from Salmonella infection without antibiotics. However, those with severe symptoms may require hospitalization.
Salmonella infection is often more severe and dangerous in certain groups of individuals,
- 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
- 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 its shell, and cracking it 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 any with cracked shells, and cooking them thoroughly before eating them.