The majority of essential oils are obtained by steam distillation in a stainless steel alembic. This is the most common, gentle and productive method of essential oil extraction.
The plants are not directly submerged in boiling water because at high temperatures the most subtle aromas might be altered.
Steam is passed at a low pressure through a tank containing aromatic plants.
The steam causes small sacs containing essential oil to burst and will naturally capture the volatile essential oil compounds that are released into the still as a vapour.
This vapour it will then travel through a cold-water refrigerated pipe to condense itself into a liquid. Since water and essential oil do not mix (essential oils are usually lipophilic compounds), the essential oil will be found on the surface of the water. Occasionally an essential oil is heavier than water and is found on the bottom rather than the top, such as with clove essential oil.
The essential oil and the water can be then be separated by their different densities. The water, referred to as a 'hydrosol' or ‘floral water’, can be retained as it will have some of the plant essence.
Absolutes are highly concentrated aromatic substances and are obtained from delicate flowers by either enfleurage (a very expensive process which has become almost obsolete) or solvent extraction. Absolutes will most often resemble the natural aroma of the plant and are normally more colored and viscous than essential oils. Absolutes are used extensively in the cosmetic and perfume industries due to their strong aromas.