How to preheat a frying pan JUN 14 2010
This blog post and accompanying videos show you how to preheat your frying pan to the precise temperature at which your food won't stick. It involves waiting until a small splash of water in the pan forms a single mercury-like ball that floats (literally!) around the pan. Too hot and the water will disperse into smaller balls; too cold and it'll just boil off instantly.
The water "hovering" over the stainless steel pan like mercury happens due to the phenomenon known as the Leidenfrost effect. You can read more about it on wikipedia, but the basic idea is this: at a certain temperature known as the Leidenfrost point (roughly around 320F for water, but varying with surface and pressure), when the water droplet hits the hot pan, the bottom part of the water vaporizes immediately on contact. The resulting gas actually suspends the water above it and creates a pocket of water vapor that slows further heat transfer between the pan and the water. Thus it evaporates more slowly than it would at lower temperatures. At the proper temperature, a similar effect happens with the food you place in the pan, preventing the food from sticking.
This is possibly the best kitchen tip I've ever heard. (thx, jim)