Distillation Of Essential Oils

Natural essential (or volatile) oils are the volatile, odoriferous oils obtained from plants. These are found in special cells, glands or ducts located in different parts of a plant such as the leaves, barks, roots, flowers and fruits and sometimes in just one or two parts. Essential oils are isolated from various plant parts such as leaves, peel, bark, root, grass, wood, resin, berries, seeds, flowers, rhizome and buds. These essential oils are extracted by either cold pressing or distillation. 

Distillation of aromatic herbs implies vaporising or liberating the oils from the plant cells in presence of temperature and moisture and then cooling the vapour mixture to separate out the oil from water. It is the most popular method in use today for producing majority of essential oils throughout the world. The apparatus used typically consist of a still or a tank in which the plant material is kept, condenser where the vapour mixture cools down and a receiver where the cooled down liquid is collected. There are three types of distillation

Water / Hydro-distillation

This process involves placing the desired plant material in a still and then submerging it into water. The water is then brought to boil. The steam generated into the system penetrates the cell wall of the plant material and the essential oil trapped is released and becomes volatile. The mixture of oil and water vapours thus generated is cooled and two distinct layers of liquid are formed. This is then collected and the oil is separated from the water. Hydro distillation is used when plant material is dried and will not be damaged when boiled. A special form of hydro distillation used in India is Deg-Bhapka. It is used to make attars and fragrant water (hydrosols).

Water & Steam / Hydro-Steam distillation

In this process the plant material is supported above the boiling water by a perforated grid or plate in the tank. The water is boiled using a furnace or heating coils. The water boils generating steam which passes through the plant material and releases the essential oil in vapour form. This vapour mixture is then passed through the condenser. The vapour cools down to form two distinct layers of oil and water in the receiver. The oil is then separated. Typical example of this system is the Field Distillation Unit.

   

Steam / Direct distillation

In Steam Distillation steam is directly applied to the plant material in the tank. The steam is generated separately and introduced into the tank by a steam line.  The steam passes through the plant material releasing the volatile oil. This vapour mixture cools when it passes through the condenser and gives two distinct layers of oil and water which is collected in a receiver.