Three food safety experts explain.

By Jenny McCoy
April 02, 2019
BRETT STEVENS/Getty Images

As an avid meal prepper and overnight oatmeal lover, I frequently fill my fridge with stacks upon stacks of tupperware. And while there’s a lot I love about these ready-made meals (chiefly, the convenience), there’s one, very specific thing that skeeves me: the condensation that seems to always form on the lid of each tupperware container.

These tiny water droplets, which typically appear within a day of popping a new container in the fridge, mildly gross me out. They also seem to make the food soggier, which is another ew. But on a more concerning note, I’ve recently wondered if this excess moisture makes my leftovers more susceptible to growing mold or otherwise going rancid.

Since I’m no food safety expert myself, I turned to three credentialed folks in the field. I asked them: What causes these droplets to form? Do they ever represent a food safety risk? And what—if anything—can I do to prevent them? Here’s what I learned.

My first question: What, exactly, causes this condensation?

Those top-of-the-lid droplets are essentially the result of “simple physics,” says , PhD, extension specialist in food science and distinguished professor at Rutgers University.

Schaffner explains it this way: Air can hold a certain amount of moisture, and that specific amount is dependent on the temperature of the air. As air cools down, it reaches a point—known as the dew point—where it is no longer capable of holding all of its moisture. When air reaches this dew point, the moisture finds a surface and condenses [i.e. turns into water] on that surface. So in the case of sealed tupperware leftovers, the moisture emitted from cooked food cools down when it’s stashed in the fridge. When that moisture reaches a cool enough temperature, some of it—thanks to the laws of physics—transforms into those water droplets.  

It makes sense, then, that foods with higher moisture contents will create more condensation when stored in tupperware and refrigerated. Many of the foods we typically save as leftovers fall into that high moisture category, says , Ph.D., certified food scientist and an adjunct associate nutrition professor at the Harvard T.H. Chan School of Public Health. Things like vegetables, which range in moisture content from 75 to 90 percent, and meats, which range from 60 to 75 percent, are big condensation culprits.

So, does this moisture ever pose a risk to the safety of the tupperware contents?

Some really relieving news: From a safety point of view, “the condensation is not a problem,” says Crosby. The only time the condensation could contain pathogens, adds Schaffner, is if the lid wasn’t properly cleaned beforehand, or if the food already contained bacteria that then spread to the lid.  

In general, there is less chance of bacteria and mold growing in the moisture condensed on the lid than in the food itself, says Crosby. That’s because the food offers a better source of fuel for the bacteria and mold than the water. (The one exception to this is high-acid foods—defined as those with a pH below 4.6—as the acidity helps protect these foods from spoilage. 

Beyond the fact that the condensation, in and of itself, doesn’t spell any danger for the food, it also “shouldn’t in any way change the texture [of the food],” says Crosby. Any mushy texture you notice in your leftovers is likely just the food breaking down over time and thus becoming soft—not added mushiness because of the condensation on the lid, he explains.

The condensation still skeeves me anyways. Is there anything I can do to prevent it?

“Without changing the laws of physics, there’s not much you can do to prevent [the condensation],” says Schaffner.

 That said, you can reduce it. One of the best ways to do so is to allow your food to cool significantly at room temperature before covering it and stashing it in the fridge, says Crosby, who recommends letting hot leftovers cool on the kitchen counter for 30 minutes to an hour. Just don’t leave ‘em out longer than 2 hours, as you increase the risk of harmful bacteria growing.

 Also, be aware that the longer you leave food uncovered on the counter, the greater opportunity that mold spores or spoilage organisms, which may be floating in the air, have to settle into the food, says Schaffner. For that reason, he recommends placing a piece of clean parchment paper on top of your leftovers as they cool on the counter to reduce the risk of this contamination. 

If you either forget to let your food cool down before stashing it in the fridge, or you do let it cool and significant condensation forms anyways, you can always remove the moisture after the fact. Just carefully open your container over the sink and simply shake off the excess water, says Schaffner.

On the topic of tupperware leftovers, are there any legitimate food safety concerns?  

When it comes to ensuring the safety of your tupperware contents, the biggest factor to manage is temperature, says Schaffner.

To avoid dangerous bacteria growth, hot food needs to be kept above 140 degrees F, and cold food needs to be stored below 40 degrees F. In the case of a hot meal becoming cold leftovers, the food needs to drop from above 140 F to below 40 F within 4 hours, says , professor in the Department of Food Science at Cornell University. The longer it takes the food to cool, the more time pathogens have to grow.

To ensure speedy, safe cooling, your tupperware containers should never be deeper than 3 inches, says Schaffner. This is a regulation in food service, and a good rule of thumb for home cooks, too, he explains, as shallow containers allow food to cool more quickly.  

If you’re trying to cool a small batch of leftovers, you can put them in the fridge with the tupperware lid vented, says Worobo. This will allow the food to cool faster than it would at room temperature. Once the food is adequately cooled, shut the lid. [At this point, you could also shake off any condensation that’s formed on the lid, if you’re still bothered by that.]

If you have a large volume of leftovers—say, after Thanksgiving dinner—immediate refrigeration is not recommended, says Worobo, as stuffing a big batch of piping hot grub into the fridge could throw off the temperature of the entire machine. Instead, cool large volumes of leftovers by stirring them, and then let them sit out at room temperature (again, for 30 minutes to an hour). You could also put your tupperware container of hot leftovers into a mini ice bath and stir the leftovers inside the container for even faster cooling, he adds.

Once the leftovers are reasonably cool, you’re good to put them in the fridge, leaving the lid vented to ensure the food cools down to below 40 degrees within that 4-hour time frame. When it’s properly cooled (stick a food thermometer in to check, says Worobo), pop on the lid.

Lastly, one more thing to watch out for: if you’re cooking on a stove without your overhead vent on, keep an eye on any condensation that might form on the hood, says Worobo. This condensation could contain Listeria, a harmful bacteria that can grow at refrigeration temperatures. If Listeria-filled condensation drips down into any food that’s not going to be reheated again, you have the potential for getting food-borne illness. This isn’t a big risk for at-home cooks (it’s more so a concern in food processing plants), “but you should just watch out for it,” says Worobo.  

The bottom line

To return to the original topic—the condensation that forms on tupperware lids—I was happy to learn there really isn’t much to fret about, at least safety-wise.  

“In the grand scheme of things in terms of food safety, it’s not high on my list of things that I worry much about,” says Schaffner. What you should concern yourself with, on the other hand, is making sure your leftovers are stored at a safe temperature within a safe time period.

That said, if those small water droplets clinging to your tupperware lids still bother you, try cooling your food before popping it in the fridge [just don’t let it sit out on your counter for more than 2 hours]. And if you’re seeing condensation anyways? Simply shake it off in the sink. With this expert knowledge and a new peace of mind, I’ll head back to my kitchen for more meal prepping.  

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