Originally posted by: yellowfiero
In addition, if he was indeed using sodium acetate, then that happened at room temperature. You mix the sodium acetate (food grade) with water, then boil until totally dissolved. Then let it cool to room temperature. By agitation, then it will instantly crystallize, like the video.
There are two different potential effects going on here. One is supercooling, where liquid water can be cooled to below freezing, but if the water is absolutely pure and the sides of the container are extremely smooth, then no seed ice crystals can form around imperfections or particles. So the water remains liquid, but as soon as someone agitates the container it freezes instantly.
The other phenomena mentioned occurs when you super saturate a solution with a solute. You heat the liquid up, add the solute to the proportion such that when you cool the liquid down it is super saturated. In other words, there is more solute in the liquid than it can actually hold. The whole thing will crystalize with sufficient agitation or by the addition of a seed crystal or some particle which the solute can form a seed crystal on/around.
As far as putting rock salt on ice in a cooler... Rock salt lowers the freezing point of liquid water. As the ice in your cooler melts to form liquid water the liquid water is a 0C, while some of the ice is well below that temperature, say -15C. The addition of rock salt allows the water to melt at a lower temperature, say -5C. Thus, the resulting solution of water and salt is colder than water alone. Since liquid water is far more effective in transferring heat than ice, if you can make your water colder, your beer will get colder, faster.
R