When I fry something on the pan and the fire is big and intensive (the flame over the pan), there is no stean above the pan or just a little. But when I turn off the fire, suddenly the steam appears, a lot of steam, and then disappear. Why is that?
Steam is caused when water vapor condenses. This is caused by the air having too much water vapor for it to hold. When you have a lot of heat under the pan, the air above the pan is quite hot and can hold a lot of water. The water evaporating from the pan disperses into the atmosphere and doesn't condense. When you turn off the heat, the pan and food stay hot for a while, but you are not heating the air above the pan as much. The cooler air above the pan gets saturated and the steam condenses. As the pan and food cool, less water evaporates and the water stops condensing.