How Can I Tell If Food Left at Room Temperature Is Safe to Eat?

Thanks to the miracle of modern refrigeration, we’re able to keep perishable foods longer and no longer have to go shopping every single day for fresh food. Though most of us probably don’t think about how amazing that is on a regular basis, we definitely pay attention when something goes wrong. If you’ve ever gotten a mouthful of chunky, spoiled milk or eaten a mayonnaise-based salad that sat in the sun too long at a picnic and later got sick because of it, you realise quickly that our ability to keep foods in cold storage is a really big deal.

So how long is too long to keep food at room temperature that’s supposed to be refrigerated? Here are a few things to keep in mind:

How long has been out of the fridge?

According to the USDA, put perishable foods in the refrigerator within two hours of purchasing it. If it’s above 90 degrees, then you only have an hour, so hop to it. This also goes for serving foods at a dinner, picnic, or other event where you have dishes sitting out for prolonged periods. If that’s the case, also try serving the perishable item in a container that is nestled in a bowl of ice.

It is a potentially hazardous food?

Potentially hazardous foods exist in a form capable of supporting rapid and progressive growth of microorganisms, according to Princeton University’s Environmental Health and Safety department. Examples include any food which consists in whole or in part of milk or milk products, eggs, meat, poultry, rice, fish, shellfish, and edible crustaceans. These foods in particular need to be served at safe temperatures. Per Princeton:

“All potentially hazardous food should be kept below 41oF (for cold foods) or above 135oF (for hot foods) except during necessary preparation time or a short display period. Hot or cold holding equipment may be required to store and display food during an event. A food thermometer is also required if potentially hazardous foods will be served.”

Has it entered the food danger zone?

Food left out for too long at room temperature is the perfect breeding ground for bacteria like Staphylococcus aureus and Salmonella to grow to dangerous levels that can cause illness. According to the USDA:

“Bacteria grow most rapidly in the range of temperatures between 40°F and 140°F, doubling in number in as little as 20 minutes. This range of temperatures is often called the ‘Danger Zone.’”

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When in doubt, throw it out

Not only does this rhyme, but it’s really important. If it’s a potentially hazardous food, err on the side of caution. Having the last few spoons of chicken salad isn’t worth getting sick over.

This story was originally published in November 2013 and was updated on October 29, 2020 to provide more information and meet Lifehacker style guidelines.