dew, water which condenses on objects, such as leaves, when the air in immediate contact with them is cooled below dew point, the temperature at which the air becomes fully saturated by its current content of water vapour (see humidity). Dew contributes little directly to the water supply of the vine. However, the latent heat of vaporization that is released during condensation plays a positive role by slowing night-time temperature drop. The risk of frost is appreciably reduced when the air contains enough water vapour to result in dew.
