Burned by the deep freeze
People from all walks of life — food writers, chefs and maybe your mom — warn of freezer burn, the bogeyman lurking in our kitchens waiting to take hold of our precious frozen foods. But what is freezer burn, and how do we stop it? And if it does latch on to a bag of chicken breasts or a loaf of bread, is all lost? Here's what you need to know. “The moisture-carrying capacity of air decreases with temperature,” said Rohan Tikekar, an associate professor of food science at the University of Maryland. In other words, cold air is drier than warm air, while food contains a relatively large amount of water. Because of this differential in moisture content, the cold air in your freezer wants to suck the water out of the food stored within it, which happens through a process called sublimation.
“During freezer storage, the conditions, particularly the temperatures, are such that water can sublimate directly from a solid state to a gaseous state that completely skips the (liquid) state,” Tikekar said. (This is why ice cubes shrink if they stay in the tray for too long.)
One way this can manifest is the ice crystals that form on the surface of food, such as a loaf of bread or that half-eaten container of ice cream. Another signal is that certain foods, particularly meat, can look shrivelled and leathery as they dry out.
Loss of moisture obviously means that produce and meat won't be as juicy. Another possible byproduct is a loss of cellular integrity, which can cause even more water within the food to ooze out when it's thawed.
For meats specifically, dehydration can cause proteins to denature, making them less tender when they're cooked.
The solution to freezer-burned food is simple: “If food does suffer from freezer burn, cut off the affected areas — before or after cooking — and use the rest of the food,” staff writer Becky Krystal wrote in a guide to using your freezer.
You can also work to stop freezer burn from happening in the first place.
“The water has to escape the packaging for it to become an issue,” Tikekar said. “So if you choose a packaging (that) is harder or (that) doesn't allow for the water vapour to pass through the container, you will have a better chance of not having freezer burn.”
Glass storage containers are a great option. If you choose plastic zip-top bags, make sure to use ones intended for the freezer as they are thicker than regular bags and thus better at sealing in moisture. With bags, in particular, you want to push out as much air as possible to minimize exposure to that cold, dry freezer air. ( Vacuum-seal bags are built for freezing if you have the equipment.) And with any container, you want a tight seal, so on freezer bags, make sure the zipper is closed end to end.
While food that's continuously frozen remains safe for consumption almost indefinitely, according to the Food and Drug Administration, your eagerness to eat it is a different story.
“Freezer burn is not a microbiological issue. It's not a food safety issue,” Tikekar said. “It's definitely, purely a food quality issue.”
This is why there are suggested limits for how long to store various foods in the freezer; with certain items, after a few months or up to a year in the deep freeze, the quality of the food may be past your point of palatability.