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  • Have you ever noticed that meat or vegetables or ice cream left too long in the freezer

  • develop a layer of frosty ice on their surface? And when eaten, they're kind of dry and icky?

  • This is freezer burn, and it happens because ice in the frozen food sublimates - that is,

  • the water changes directly from a solid to a gas rather than first melting and then evaporating.

  • Unlike regular frost (also called "hoar frost"), which forms when water vapor that's already

  • in the air freezes into crystals on top of something cold, the frost in freezer burn

  • comes from frozen water in the food itself. That's why freezer burn happens less to flour

  • and nuts than to vegetables and meat and ice cream, which contain more water. And the ultimate

  • effect is that water is transferred from inside the food to outside the food, leaving it dry

  • and frosty, but still safe to eat. You're basically freeze-drying it, although the food

  • might also oxidize and turn brown.

  • Of course, ice by itself can also sublimate, which is why ice cubes shrink in their trays

  • over time. And the frost on the walls of a freezer comes partly from water that was once

  • in ice cubes and food in the freezer.

  • Sublimation happens more easily when the air is dry and when the ice is close to the melting

  • point of water, so you can avoid having your food get freezer burn by keeping your freezer

  • consistently cold and preventing air from contacting the food in it - for example, by

  • sealing food in plastic freezer bags without any air pockets.

  • What's more, freezer burn ISN'T just limited to freezers - it happens in nature, too. Frost-flowers

  • on sea ice, for example, form when water vapor sublimates from warm ice into air too cold

  • to hold it. Homeless, the vapor deposits back onto the surface as icy lilies - sublime sublimation.

Have you ever noticed that meat or vegetables or ice cream left too long in the freezer

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什麼是凍燒? What is Freezer Burn?

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