For years, I've been teaching about supercooled water, or quick ice, in my Science of Everyday Things class. I usually introduce the idea by asking "If some liquid water in your hand were to spontaneously freeze, what would it feel like, hot or cold?" I use this question to help reinforce the idea of phase change energy, since the students have to recognize that when a liquid freezes it has to give off its heat of fusion, thus making the hypothetical hand hot.
"But you can't really make water spontaneously freeze, can you?" I'll then ask. Then we play with supersaturated sodium acetate hand-warmers, like these. This type of hand-warmer consists of a flexible plastic packet containing sodium acetate and a little bit of water. When you place them in boiling water, the sodium acetate dissolves into a liquid state. Then when the packs cool down, the solution stays in a liquid phase. By clicking a small metal disk, the liquid solution crystallizes into a slushy solid, giving off heat in the process. It's a memorable experience to see the liquid heat packs spontaneously freeze in a matter of seconds.
At this point, I always talk about supercooled water, or quick ice. Years ago, my supervising teacher during my student teaching experience told me how he had found a cider bottle full of quick ice on his front porch one morning, and it froze while he was carrying it inside. I always figured it must be pretty hard to supercool water, or you'd hear about it more. Then on February 7, 2007 I discovered that four drinking water bottles in a refrigerator in my garage had become supercooled.
After teaching about the stuff so long, I was excited to finally see it for myself. I took one of the bottles and gave it a shake, watching as it froze from the top down. I got out my video camera and tried a few other things and made this video:
The video shows a full case of drinking water that I left in my cold garage overnight on the seventh. Every bottle became supercooled- the outdoor temperature was about 14 oF when I filmed the video.
I have not been able to create supercooled water in my kitchen freezer. I suspect that it's due to the vibrations from the fan blowing inside the frost-free freezer. I've tried to make quickice in our big deep-freeze, and even though it doesn't have a fan, I've never made quickice there either. I have received several emails from YouTube viewers who have made quickice in their freezers though- they've generally done it with drinking water bottles that were left in the freezer for 2-3 hours.
In the YouTube comments section of my video there have been several users who have expressed skepticism about whether the water was really freezing. I don't know if they're serious or if they're just trolling for a fight, but I would encourage them to just try it for themselves.