Who wants a neverending supply of frozen Coke? The answer should be no one, because it would definitely kill you, but for anyone looking for a moderate supply of slushies that can be delivered straight from your very own freezer, Grant Thompson aka The King of Random on YouTube has got you covered with this awesome video. The technique works with any type of sports or soft drink in a bottle or can, and all you need is some freezer space and about 3 hours of waiting time. (Which I guess makes it a 3-hour slush-- shhh stop ruining it.)
As the video above explains, you need to take your soft drink, shake it violently to build up as much pressure as possible inside, and then put it in the freezer. Depending on what temperature your freezer is set to, you'll need to leave it in there for between 2.5 and 3.5 hours, and take it out when the liquid inside is colder than freezing, but not actually frozen. It could take a few attempts to figuring out your timing.
When your supercooled drink comes out of the freezer, it will look perfectly normal, but release the pressure and turn it upside-down, and in 3 seconds the whole thing will take on an icey consistency. Another option is freezing a bowl alongside it and instead of turning the drink upside-down first, just pour it straight into the bowl for more instant freezing. Pour it in a bowl that hasn't been frozen and drop a tiny flake of ice in and watch the ice spread like a virus.
So what's going on here? One explanation is that to make any kind of soft drink, a whole lot of chemicals need to be added to water, and these additives or solutes actually cause the freezing point of the water to decrease - but only so long as the bottle is sealed. As soon as it's opened and carbon dioxide is let in, the additives are suddenly diluted, and the freezing point of the water rises back up, which causes the instant slushie effect.
That's one explanation. Over at Steve Spangler Science, Joe Franek from the Department of Chemistry at the University of Minnesota in the US, offers another one:
"The more likely explanation is that you have a SUPERCOOLED solution that is simply waiting for something to allow it to begin freezing. Opening the bottle allows carbon dioxide bubbles to form and these bubbles provide a place for the nucleation of the ice crystals to begin occurring. You can test this explanation by tapping the chilled bottle without opening it. You should manage to get some bubble formation from the tapping and you should see the freezing occur."
The process of chilling a liquid to below its normal freezing point without turning it into a solid is known as supercooling, and it occurs when there are no 'seed crystals' in the liquid to act as a nucleus around which an ice crystalline structure can form. By shaking up the bottle before you put it in the freezer, you're actively eliminating any large bubbles in the soft drink that can act as sites of ice crystal formation. Once you open it up again, it will fill up with large bubbles once more so the ice crystals can spread.
You can see this explanation in video form below (horrible awkwardness ahead, you've been warned), and apologies for telling you about this right when summer has just ended for many of you. At least you'll be a DIY slushie pro in time for next summer.