We all know the situation.
The party is about to begin, it's really hot outside and we forget to put the beer (or similar drink) into the fridge...
What is your way to chill beer really fast?
Use a salted ice-water bath. The water increases the contact and heat dissipation, and adding salt allows the temperature to go below freezing.
The mythbusters actually did this one once, and their conclusion was that the best and easiest way was indeed to simply add some salt to the water.
I've used this for chilling wine and long necks.
This works for cans of beer.
Using this method I can cool a beer that's been sitting out in the sun in under two minutes.
I agree with Kevin's salted ice-water bath, but I find chucking a few tinnies in the freezer works as well. Just remember to remove them on time or you're going to have a bit of a clean-up job.
Here comes the science!
The Goal: Transfer heat from the warm object to the surrounding environment, as quickly as possible.
Discussing point 3, the corollary is that when ice melts at 0 degrees C, it takes a whole lot of heat to break the crystal lattice and convert to liquid. This means that melting ice will "grab" heat out of the beer faster than solid ice warming up, or liquid water warming up.
So at this stage, what we want is ice mixed with water, just below the melting point. Add beer cans, and the beer will "suck the cold" out of the ice as it melts, bringing the entire system near to freezing fairly quickly. (in a matter of 10 -15 minutes).
Still not fast enough? Then we need to go to a different universe where the melting point of water is colder. (Or add salt to the water, which will lower the melting point, causing the whole reaction to occur at a lower temperature, giving us a speed boost as to Bullet #2.)
Still not fast enough? -- Well, if you've got liquid nitrogen on hand, you're over prepared for your unpreparedness. You could have just stuck the beers in the fridge.
I throw my brew right into the ice cube reservoir in the ice-maker in my freezer. This way it sits in ice as well as is in the freezer at zero degrees. I apply this to champagne as well, and it actually works well.
Wrap the beers in wet paper towels or wet rags and put in the freezer. Its really is quite effective and doesn't need salt or ice. This video shows what a difference it can make: http://youtu.be/Nf8rKvZWQrY
A bit un-exciting but.
I usually put a bottle/can in the freezer and put a timer on 15 minutes.
Or, if it is really urgent, pour into a glass and add 3-4 ice cubes. Heresy, I know, but it creates something cool to drink fast.
Water bath is best as suggested (I am not going to write that out again), but if you want to do it even faster then get the water moving around too.
A small pump that just pumps the water back in at an angle will do (I am thinking large fish tank one OR water fountain). A good whirl pool effect is fine if it is white wine but not so much as to fizz up the beer mind!
You should be abel to cool a whole case in just a few minutes.