Steam distillation
The most widely used method for extracting plant essential oil is steam
distillation [4, 32]. steam distillation is the process of
distilling plant material with the steam generated outside the still in
a stand-alone boiler (figure 4). As the steam-water distillation system,
the plant material is placed on top of a perforated gird above the steam
inlet [23]. both water and steam in this method, are utilized, but
the plant material is not in direct contact with water and steam
generated outside the still in a boiler and flows through a pipe into
the bottom of the steel. A mixture of water and oil are vapored and
condensed. Finally, the oil is separated from the water by a separator.
steam is always fully saturated, wet, and never superheated in this
method [7, 33]. Also thermal degradation of components does not
occur and amount of steam is adjustable. Of course, this method is more
expensive than the hydro-distillation and water-steam distillation.
Boutekedjiret is
reported extraction of rosemary essential oil by steam distillation
[34]. Also E. Cassel succeeded in extracting of rosemary, basil and
lavender oils with 0.51%, 0.38% and 0.32% (w/w), respectively
[35].