6/21/11: This is an older page - and basically wrong - I found it can damage the coffee flavor, and reduces the shelf life of the coffee basically. Tom
A lot of the control you need to produce consistent roasts depends upon your cooling method. Your local shop roaster dumps the beans from a roast chamber into a perforated metal cooler with a rotating arm that agitates the beans. Air is evacuated from the bottom (sometimes from the sides too) and heat rises from the top, so cooling happens fairly quick.
Under most conditions you should simply allow coffee to cool in a room temperature environment, or by fanning the air over and through the coffee.
But a few times I have had trouble cooling beans when I roast in very hot weather, and have failed to stop many of my City roasts from becoming Full City roasts, and French from becoming Dark French. Therefore, in these conditions I sprits my coffee with a VERY fine mist from a spray bottle of good clean filtered water after I dump the beans in a colander. I mist them only as long as the water seems to evaporate immediately from the surface. I usually mist a couple times, then stir a couple times, then mist ... for no more than 30 seconds usually.
Are you actually cooling the coffee by wetting it? No! That's exactly what you don't want to to do. The idea is that the energy expended to turn the moist air around the coffee into steam expends the energy stored as heat in the beans. So you are misting the air around the coffee so it uses energy and therefore loses heat.
For most of the year I simply cool my roasts by stirring and shaking them in a metal colander. Use a colander that has a lot of holes and is made from aluminum. A steel colander will heat up quickly and keep its temperature, which doesn't really aid the beans in cooling. The exception is a wire mesh bottom steel colander that does an excellent job dissipating heat.
Ken Davids' Home Coffee Roasting warns of the dangers of soaking the beans in water to cool them. I haven't had a problem with my method, since I am very conservative, but shaking and stirring works fine if the use of water makes you worry.