Water or steam distillation is one of the oldest processes of extraction, or separation, of organic substances, brought by the Arabs in the ninth century. This technique was already known by the ancient Greeks, and probably dates back to the Egyptians, around 3500 BC.
It is accomplished in a distillation apparatus . The method is based on the existence of an azeotrope having a boiling point lower than the boiling points of the two pure compounds taken separately.
The goal is to draw with steam the volatile components of the crude products. The steam destroys the structure of the plant cells, and releases the molecules contained. It then catches the more volatile ones, separating them from the cellulosic substrate. The steam charged with the essence of the distilled raw material condenses in the coil before it is recovered in a still receiver.
The insolubles in the condensate are decanted to obtain the supernatant oil (or essential oil). The part containing the water soluble compounds is called herbal distillate (or hydrosol) . The manufacturer then collects a mixture of defined composition of the two products.