@aaronpk I remember doing a science experiement in elementary school involving several 2 liter bottles of generic cola from the local store and a very cold day (I think it was 22ºF/-6ºC?) doing exactly this in our schoolyard. Very fun, and very cold.
@aaronpk I heard stories about this from my Dad, who grew up as a kid in South Dakota. This would happen in water troughs inside barns. You get below freezing outside temps, and the barn could hover at 32 or below, and the water could be made to freeze over by just touching it, creating the first little nucleus/crystallization point and physics would take over from there.
@aaronpk
you missed the simpler explanation:
You. Are. Magic.
@aaronpk My favorite instance of this I’ve seen was a bottle of carbonated water that got left in a freezer just a bit too long. It was liquid, I pulled it out and gave the cap a half-twist and it froze from top to bottom, moving in a wave, over the course of about three seconds. Looked really neat and I’ve never duplicated it.
@aaronpk Could be the sugar content in the syrup + the carbonation and it's dark colored so pretty easy to see the changeover when it happens through the fizziness.