On Freezer Burn

A friend recently asked me about freezer burn. It certainly isn't a standard burn from heat or acid, so what causes it? Why is it that food left in a freezer - and theoretically locked in some sort of suspended animation - nevertheless goes bad? How can it best be prevented? He also asked about how freezer burn can "tenderize" meat, which is something I've never heard of but decided to look into.

Not exactly ideal.

The "what" of the situation is simple. A majority of what we call freezer burn results from food drying out. It may sound crazy for food that's no longer "wet" to lose water, but the molecules that comprise ice aren't as calm as you may think they are. They're constantly vibrating on an atomic level, and every so often one molecule manages to break free and enters the air as water vapor. This process of going directly from a solid to a gas is known as sublimation. A small amount of freezer burn comes from oxidation through exposure to air. Although the cold temperature slows down the process of oxidation, any access to air will nevertheless allow it to occur. An cut apple browns quickly in open air; a frozen cut apple will still brown, it will just take longer. Freezer burned food is fortunately safe to eat. There's nothing harmful about it. However, it might have a rubbery texture or taste a bit funny.

What can we do about it? Colder freezers will theoretically make sure that the ice within vibrates with less energy, but that type of power really isn't practical within the home. Instead, the easiest thing you can do is to just make sure you wrap your food well when you put it in the freezer. Whenever I buy a lot of meat, I take it out of the packaging it comes in. I then wrap smaller portions in plastic wrap, and then put those within a zip lock bag. It's a trick I picked up from my mom, and it's helped me to have lots of meat in my freezer that pretty much never gets freezer burn. Having the double layer of protection helps prevent oxidation as well. It's doubly convenient because it makes it really easy to defrost exactly how much you need rather than an entire package of meat. A minor way of preventing freezer burn is to have a lot of ice in your freezer. Water molecules coming off the pure ice will start to saturate the air with water vapor, making it more difficult for additional molecules to come off your foods.

As for tenderizing? Freezer burn has nothing to do with it as far as I've been able to find. Freezing in general will change the structure of the food, but not in the desirable way that tenderizing does. Instead, ice crystals grow within the cells of the meat or vegetable, creating strange pockets and rupturing cells. As a result, foods that have been frozen and thawed (especially raw foods) rarely taste and cook quite the same way as fresh. They tend to lose more water, salt, and oil when being cooked. The best way to minimize this effect is to freeze food as quickly as possible - freeze it in small pieces, and with the freezer temperature set down low.