Steam distillation is the most common method of extracting essential oils. Steam distillation is done in a still (The still is tall with a head and a well-insulated swan's neck preceded by a mechanism to prevent fumes and impurities passing through). Fresh, or sometimes dried, botanical material is placed in a closed container of the still, and pressurized steam is generated which enters the container and circulates through the plant material. The heat of the steam forces the intercellular pockets that hold the essential oils to open and release them. The temperature of the steam should not be very high as it can damage the botanical material but should be high enough to open the pockets which hold the essential oil.
Tiny droplets of essential oil evaporate and attach to the steam. The steam which then contains the essential oil, is passed through a cooling system to condense the steam, which forms a liquid from which the essential oil and water is then separated by decantation. The oil forms a layer on the water surface as it does not dissolves in water and hence is separated easily.
This method is not used for extraction of oils that are sensitive to heat.