The best way to freeze and defrost your food, according to the experts

For many of us, freezers serve as a sort of black hole for our leftovers and miscellaneous food items. Everything from half-eaten cartons of ice cream to Thanksgiving leftovers tend to find a home in the freezer—sometimes indefinitely. 

 Though it’s a convenient catch-all for extra food, the freezer can also be a source of some confusion and even, if used improperly, food-borne illness. You might wonder, for instance, whether it’s OK to put steaming-hot leftovers directly in the freezer. Also: Is that partially crystallized muffin still safe to eat? And what should you do with unidentifiable red sauce that’s been thawed and refrozen a few times?

Experts weigh in on frozen food safety and tips for best freezer hygiene. 

Should you cool hot food before freezing? How quickly does food have to get in the freezer?

Leaving food out at room temperature can increase the risk of pathogen contamination and growth. For safety reasons,“leftovers should be put away in two hours,” says Keith Schneider, a food safety microbiologist and professor of food, science and human nutrition at the University of Florida.

This rule is especially important with foods that require refrigeration or freezing—such as raw meat, poultry, seafood, eggs, and fresh produce—which should not “sit at room temperature for more than two hours—one hour if the air temperature is above 90°F,” according to the FDA.

From a safety perspective, it’s OK to put hot food directly in the freezer without chilling it first, according to an official from the U.S. Food and Drug Administration.

While it’s possible that directly storing hot dishes in the freezer could elevate its internal temperature, for home cooks and home freezers, the volume of food is generally small enough to have only a marginal and temporary impact, says Alejandro Castillo, a professor of food microbiology and food safety at Texas A&M University.

If you want to be extra safe, you can wait until the food is 130°F and/or split hot food into “smaller, four-inch containers, which allow for proper airflow and heat dissipation,” Schneider says.

Got some refrigerated leftovers that you’re not going to eat any time soon? It’s perfectly safe, even advisable, to move those into the freezer for longer-term storage, according to Castillo. That said, “freezing doesn’t turn back the hands of time,” Schneider warns. Pay attention to dates: If the food has already spent two of its four-day shelf life in the fridge, then you’ll only have two more days if it goes back into the fridge to re-thaw. 

How long can foods be frozen and still safe to defrost and eat?

While quality might degrade over time, rest assured, that frozen bagel can sit safely in the freezer for years. “Freezer burn,” when frozen food dehydrates due to exposure to cold air—sometimes appearing as a layer of frost—is not an indication food has gone bad but may affect its taste and texture.

With proper food handling and storage, freezers kept at 0°F act as a sort of time capsule, preserving all food indefinitely. “While freezing does not kill most bacteria, it does stop bacteria from growing,” according to the FDA.

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Perhaps more important than your freezing technique is your food and kitchen hygiene. “If you freeze contaminated food, you’re going to preserve it with everything that’s in it,” Castillo says. He recommends keeping a clean kitchen and fridge, and separating raw from ready-to-eat foods, to avoid unnecessary cross-contamination.

Proper packaging preserves quality by avoiding freezer burn or other chemical changes, Schneider says. But when it comes to food safety, he adds, “If it’s [below] 38°F no pathogens are going to grow.” Case in point: “I found a filet mignon that I had—I wasn't going to throw it away—for two years, and it was vacuum sealed, and it was tasty.” 

But that doesn’t mean you should stuff your freezer with food for the apocalypse. Freezers rely on fans that blow cool air around the food and won’t work as well in a jam-packed environment, Schneider explains. “If you overstuff a refrigerator or freezer, you reduce the airflow, and things will not cool fast enough.”

What are best safety practices for defrosting food?

As a rule of thumb, defrosting should happen as quickly and evenly as possible to prevent any bacterial growth. The FDA recommends three primary methods of defrosting: in the refrigerator, cold water, or a microwave. Anything thawed in cold water or a microwave should immediately be cooked, and food should never thaw at room temperature, including on the countertop.

“The reason is, even while you’re defrosting, you don’t want to heat up the outside of the meat while the inside stays cold,” Schneider says. That would mean the outside reaches a temperature range favorable to bacterial growth while the inside continues defrosting. He suggests using a cold water bath to thaw food at a consistent temperature that avoids this “danger zone.”

If time isn’t an issue, refrigerators are ideal for thawing in a safe, constant temperature, according to the FDA. But, they add, “if you need an item immediately, opt to cook foods from the frozen state.”

Is it safe to defrost food and then freeze it again?

Defrosting and refreezing requires care, according to experts. Every time you defrost an item, it enters the “danger” temperature zone where microbes can start to grow and produce toxins. 

Food thawed in the refrigerator can be safely refrozen without cooking, but anything thawed in cold water or a microwave should be cooked before going back into the freezer, the FDA says.

While there’s no absolute number, “you don’t want to freeze-thaw too often,” Schneider says. He recommends not thawing and refreezing more than two or three times, though exactly how many depends on the speed and method of defrosting. “Especially if it takes a long time to defrost,” he says, bacteria can start to proliferate. “Once you hit 40 degrees the clock starts.”

How long is frozen food safe in a power outage?

If you can manage to keep the freezer door closed, your frozen goods can last for at least a few days. 

“It will take several days for your freezer to reach 40 degrees,” Schneider says. “Once you hit that point, now you have to start worrying about bacteria or pathogens proliferating.”

In this case, an overstuffed freezer might actually come in handy. “If It’s jam-packed full of stuff…the amount of ice in there or frozen products will keep the other products cool.” According to the FDA, food can last up to 48 hours in a full freezer and 24 hours in a half-full freezer.

The FDA recommends putting a thermometer in the freezer to verify the internal temperature. If the temperature reads below 40° F when the power comes back on, the food is safe to be refrozen.