When Is It Safe to Eat Moldy Food?

When is it still okay to eat moldy food? Are any molds edible? How important is it to follow those "sell by" dates printed on my egg carton? 

Sabrina Stierwalt, PhD
5-minute read
Episode #172

How to Avoid Moldy Food

So how can you keep mold growth to a minimum? Mold likes humidity, and although mold grows best in warmer temperatures, it will still grow in places that are cold if they are also moist, like the refrigerator. The best way to stave off mold is to properly store any perishables – don’t leave food that requires refrigeration out at room temperature for more than two to three hours - and to eat foods before they have a chance to grow mold. For example, leftovers, even when stored at refrigerator temperatures, should still be eaten within three to four days.

The USDA recommends cleaning the inside of your refrigerator once every few months with 1 tablespoon of baking soda dissolved in water. If you find a moldy item, that is a good time to clean because mold spores can transfer to other foods through the air. Mold spreads particularly fast among fruits and vegetables in the same drawer. To minimize the transfer, the USDA further suggest making sure food is covered.

Also don’t sniff the moldy item! Any bacteria present could enter your nose and lead to respiratory problems.

Check out the Nutrition Diva’s nine tips for reducing food waste before your food gets moldy, including planning your meals ahead of time.

Should I Really Follow Expiration Dates?

We have all likely performed the sniff test on our milk. Can I get one more bowl of cereal or one more cup of coffee out of this milk? What if the carton is past its sell by date?

We often wrongly assume that food items should never be consumed after any date printed on their container. However, only infant formula is required by federal law to have an expiration date. Thus most printed dates are not meant to reflect safety standards but instead are meant to tell you when the product will be of the best quality.

It is generally a good idea to follow “use by” dates on food, although many foods are still safe to eat after their “use by” date if stored properly. However, these dates are moot if food that should be refrigerated is left out for more than two to three hours, even if it is re-refrigerated later.

Dates marked “sell by” are much more flexible in their shelf life once you have purchased them. You should always purchase items before their “sell by” date, and the USDA has a handy table, which details the safety period for different foods beyond their those dates once you have brought them home. For example, expiration dates on eggs—which are not required by federal law but are mandated in a few states—can be considered sell by dates. Once you purchase eggs before the date printed on the carton, they are safe to keep in your refrigerator for three to five weeks (which usually surpasses the sell by date) before they need to be tossed.

Keep in mind that both “sell by” and “use by” dates will be drastically shortened if sealed packaging is opened. Freezing a product before it’s window of freshness, on the other hand, will further keep the product safe to consume indefinitely, but only until it is thawed at which point it should be eaten within 24 hours.

There are only a few foods that won’t eventually go bad, like honey which has been found in the ancient tombs of Egypt. So it is wise to pay attention to any warning signs. Spoilage bacteria can cause unusual odors, flavors and appearances, so if something seems off, stop eating!

Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com

Images courtesy of Shutterstock.


About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.

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