Distillation
Separating scented oil from plant material by heating it with water or steam and cooling the vapour.
Also: steam distillation, hydrodistillation
In distillation, flowers are heated with water, or steam is passed through them. The steam carries off the scented oils. When the vapour is cooled it turns back to liquid, and the oil separates from the water. The oil is the essential oil. The scented water left behind is a hydrosol, such as rose water or orange flower water. The method is very old and was refined by scholars and perfumers of the medieval Islamic world.