This method makes use of water and heat to achieve separation of the essential oil from the plant material. During hydrodistillation, plant matter is boiled in water, and the water vapour plus volatile essential oil components are condensed back into liquid form through cooling. Since essential oils float on water, separation is straightforward. Steam distillation uses steam to cause evaporation of the volatile components. During this process, plant matter is placed in a closed chamber, and steam is passed through it, which again causes the volatile compounds in the plant to evaporate. In the final step, as in hydrodistillation, the water and essential oil are condensed and then separated, leaving just the pure essential oil.
Hydrosols, also known as hydrolats, are approximately 99.95% water. Like essential oils, they are produced using distillation. When the water and essential oil separate, the water also carries a very low concentration of aromatic molecules – especially the ones with greater water solubility. Because the concentration of aromatic molecules is so low, they do not separate but remain dissolved in the water. Hydrosols are often used for baths, gargling, sprays, and for children’s ailments.
The key to producing a therapeutic-grade essential oil is to preserve as many of the delicate aromatic compounds within the essential oil as possible.
To begin with, in order to produce a single kg of essential oil, enormous quantities of plants are required: 250 kg of lavender, and so forth. The oils are stored in tiny cavities or ducts within the plant. Other oils provide small yields in general. For example, Bay Leaf can be expected to provide a 3 percent yield during distillation, whereas Rose Petals typically provide only a .006 percent yield.