Though it’s mostly just a party trick, the ability to instantly freeze a bottle of beer does make for one fun science experiment:
To do the trick yourself, just put a few unopened bottles of beer in your freezer and wait for a couple of hours. (Note that this works best with clear bottles like Corona.) When you open the freezer again, a few of the bottles will likely have frozen and exploded, but there should be a few that are still in a liquid state. Carefully pick up one of the liquid bottles, set it on a table, remove the bottle cap, and give it a good tap on the table. As the bubbles form, the beer will instantly freeze, as seen in the video.
So what’s going on?
It’s an effect called supercooling, and according to Wikipedia,
Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid.
A liquid below its standard freezing point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form. However, lacking any such nucleus, the liquid phase can be maintained all the way down to the temperature at which crystal homogeneous nucleation occurs.
So basically, the beer is cold enough to freeze, but it has nothing to freeze around, so it stays liquid. When you tap the bottle on the table, the bubbles create a seed and the ice forms around that seed.
(Caution: This trick involves a glass bottle filled with supercooled liquid that expands as it freezes. That chances of the bottle exploding are low, but technically it’s still possible, so you should probably wear gloves and safety glasses if you’re going to try this at home. And please, don’t let your kids handle the bottles!)