Wet steam is undesirable as it has less energy than dry steam and more importantly can cause wet loads. The packaging used for sterile products prevents reinfection when dry, but its bacterial retentive properties will be adversely affected by the presence of moisture. Wet loads can be considered to be un-sterile. The dryness fraction describes how dry steam is, with a value of 1 representing steam that is 100% dry, and therefore free of entrained moisture. Steam with a dryness fraction of 0.99 consists of 99% steam and 1% water. If we measure the latent heat present in steam that has a dryness fraction of 0.99 we will find that it possesses 99% of the full quotient of latent heat.
