Science debunks a wasteful myth about frozen food
Let’s talk freezer burn.
In many kitchens, the freezer is both a place of chilled serendipity (oh look, there’s the emergency pizza and some ice cream) and a gaping maw of frozen disorder.
With frozen vegetables, fruits, leftover soup, and chicken tenders all elbowing for space in these small iceboxes, it’s no wonder that many items get left behind and forgotten about for months — or even years — at the back of our freezers. And while a freezer will keep items safe from spoiling microorganisms that might thrive at cooler, fridge temperatures, even the 0 degrees Fahrenheit chill of your freezer can’t keep your food pristine forever.
Enter: freezer burn. You’ll recognize it by the shriveled, leather-like surface it leaves behind on meat or the crispy patches of ice crystals left in bags of vegetables.
If your frozen food is discolored that doesn’t necessarily mean it’s gone bad, but it likely means it is freeze burned.
Even though it may look unappetizing, Shelly Schmidt, professor of food chemistry at the University of Illinois at Urbana-Champaign, tells Inverse there’s nothing dangerous about these discolored foods.
But the issue for the consumer is that, while you technically can eat freezer-burned food, it won’t be very good — despite what you may have been told about throwing your leftovers into the cold. Sure, a freezer makes your food last longer — but it can’t deliver on the promise of flavor.
Interestingly enough, the same chemical process driving freezer burn is also what makes it possible to feed astronauts in space — freeze-drying.
“Here are two processes, that rely on the same transformation but because we change the conditions in the freeze-drying... it [becomes] a profitable good thing,” says Schmidt.
What is freezer burn?
While freezer burn may seem like the capricious scourge of your kitchen appliance, Schmidt assures Inverse it’s actually just a form of dehydration that takes place at cold temperature when items (from food to snow) are exposed to open air.
“I like the idea that we’ve harnessed something that’s happening to make something beneficial.”
The process is similar to evaporation, Schmidt explains, except instead of liquid water transforming into vapor, freezer burn happens when a frozen liquid transforms directly into vapor. Skipping phase states like this, not first transforming from ice to liquid water, is called sublimation.
“A similar thing that you may have seen related to this idea of freezer burn is if you have ice cubes in the freezer for a long time and don't use them, they shrink,” Schmidt says. “And the reason they're shrinking is because they're also going through dehydration — but they're all water!”
In the case of food items, hydration is drawn out during this sublimation process and then redeposited on the food’s surface as ice crystals. This can often leave foods discolored with an unpleasant, shriveled texture.
Freezer burn can take place after only a few months (depending on how air-tight you’ve sealed your food) but is ultimately an example of food in your freezer trying to regain equilibrium of vapor pressure between its surface water and water in the air.
Is freezer-burned food dangerous?
Icy food may not look as appetizing, but it doesn’t necessarily mean it puts you at risk, explains Schmidt. In fact, this process likely doesn’t impact the total nutrients of the food either — though Schmidt says more research is needed to know for sure.
Ultimately, it comes down to a flavor and texture preference, she says. When she recently tested out her daughter’s new air fryer on some freezer burnt green beans, Schmidt says the difference was noticeable.
“They weren’t as good,” she says. “The texture just wasn’t the same and they tasted flat.”
While subpar green beans may be salvageable, a rubbery chicken breast or ice crystal-covered piece of bread might not be.
How to save food from freezer burn
There are two main considerations to keep in mind when protecting your food from freezer burn, reveals Schmidt:
- Air in your container or bag
- The exposed surface area of your food
Vacuum sealing your food can be one of the best defenses against freezer burn because it removes the air that drives the sublimation process. Schmidt also says limiting the exposed surface area of your food, e.g. storing chicken breasts together instead of separately, can also help prevent freezer burn because ice formed on the product will sublimate first before the food itself.
Your food might also benefit from an old-fashioned freezer, says Schmidt, that doesn’t automatically self-defrost every few hours. While this innovation is designed to keep ice from forming along the sides of your freezer, she says it can actually worsen the process of freezer burn.
Unlike freezer-burned food, freeze-dried food maintains its flavor and texture once rehydrated.
The benefits of freezer burn
Uncontrolled freezer burn is never going to make food taste good. However, when this chemical process is controlled and done in a vacuum it transforms entirely into a space-age marvel: freeze-drying.
“I like the idea that we’ve harnessed something that’s happening naturally — freezer burn — to make something beneficial,” says Schmidt.
Because freeze-drying happens much more quickly than freezer burn — only a matter of hours or days — Schmidt says food doesn’t lose its integrity and flavor the same way freezer burnt food does.
So while it may be a pain to discover your favorite food crusted over in ice, you can sleep soundly knowing this same scientific process made it possible for Apollo astronauts to dine in space — and even for you to dine on the “astronaut ice cream” you picked up at your local science museum.
CHECK, PLEASE is an Inverse series that uses biology, chemistry, and physics to debunk the biggest food myths and assumptions.
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