(Intro)

It's Monday night, and you just got home. You're too exhausted to actually cook a decent meal, so you reach into the freezer and pull out a frozen dinner from the back. Your stomach rumbles. You open the box and pull out your lasagna and... Noooo! Freezer burn. Everything's covered in a thick layer of stale-smelling ice crystals, and you know your dinner is ruined. It's a common thing. Any food you leave in the freezer too long is eventually going to end up about as appealing as a dead Tauntaun. Why, you ask? Because it’s drying up.

See, there are frozen water molecules in your steak, or ice cream, or bag of corn. And over time, in the dry air of your freezer, some of those molecules tend to sublimate, in other words, they go directly from solid ice to water vapor. You may have noticed this happening to ice cubes, too. It’s why they slowly shrink in their trays when you could've sworn you filled them up all the way.
The molecules will often then re-freeze somewhere else, like on the package or as part of the gigantic frost wall that’s threatening to slowly take over your entire freezer. But either way, your food isn’t getting its moisture back, it ends up dehydrated and discolored, not to mention puckered and gray and generally unappetizing.
You can help delay freezer burn by double-wrapping foods and sealing them in air-tight containers to reduce their exposure to air, but if you leave food in your freezer long enough, eventually sublimation is going to ruin your dinner plans. The good news, if you can call it that, is that frozen foods don't decay, so while freezer-burned food might look and smell terrible, it's probably still safe to eat, technically.   Thanks for asking, and thanks especially to all of our patrons on Patreon who keep these answers coming. If you’d like to submit questions to be answered, or get some videos a few days early, go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow and subscribe!