Maybe you’re seeing visual cues, like a runny consistency in the egg whites, scientifically known as the albumen, or discoloration (bacterial contamination might cause the albumen to turn a greenish or iridescent color). Trash it! Note that if you see a blood spot on the egg yolk, that’s completely normal—it’s caused by a ruptured blood vessel. Cooked properly, the egg is safe to consume.
If you open up the carton to find that one of the eggshells has cracked, it’s best to discard that egg. Cracks in an eggshell—however small—open up an avenue for bacteria to get inside the egg, accelerating the process of spoilage. Here’s the golden rule: When in doubt, toss the maybe-rotten egg out. Make some oatmeal and get on with your day.
Note that there’s a difference between everyday bacterial spoilage and salmonella contamination. “It’s typically not the pathogens”—like salmonella—“that cause foods to look or smell gross,” says Dr. Schaffner. “It’s the spoilage organisms. They’re not going to make us sick, but they make the food unappetizing.”
Will eating an older egg give you food poisoning? Probably not, but it probably won’t taste very good, either. The real danger lies in the salmonella bacteria, which is not perceptible by taste, smell, or appearance.
Here’s the bad news: Salmonella is only detectable under a microscope, so the average person has no way to know if their egg is infected. “Just because the egg looks and smells okay doesn’t mean that salmonella is absent,” Dr. Schaffner warns.
The good news: Only about three out of every 10,000 eggs might contain salmonella in the albumen, so the chances of your carton being contaminated are quite low. Still, in case you do have one of those bad eggs, there are precautions you can take to curtail bacterial growth.
Salmonella lives in the albumen (or whites) of an egg, where a number of natural preservatives keep the bacteria in check. But as an egg ages, the yolk membrane—which separates the egg white from the yolk—starts to break down. Over time, salmonella bacteria may be able to breach into the yolk, where it’s able to run rampant. This means that as an egg ages, the risk of salmonella multiplying increases—but there are a few steps you can take to ward against this. The most important factor? Temperature.
“The lower the temperature, the slower the breakdown of that yolk membrane. Below a certain temperature, salmonella won’t be able to grow,” explains Dr. Schaffner. To discourage the spread of pathogenic bacteria, make sure your fridge is set to 40°F or lower.
Note that cooking an egg with salmonella to a temperature of at least 150°F will kill the bacteria. When handled properly, even a contaminated egg can be used in baking or other applications where the entire egg will be cooked through (i.e. no runny yolks).
How to preserve the shelf life of your eggs:
With proper storage, eggs should last for weeks in your fridge. But there are a few precautions you can take to keep your eggs fresher for longer. Here are a few shopping tips and other recommendations to prolong the life of your eggs.
Choose your carton wisely.
Brands are not required to print use-by or expiration dates on their eggs, but if they do, they have to follow a few rules. If the carton lists an expiration or sell-by date, it “can be no more than 30 days from the day the eggs were packed into the carton,” according to the USDA, whereas use-by or best-before dates can be 45 days from the eggs’ pack date. Paying attention to these labels can help you determine which eggs in the aisle are freshest.