Distillation of perfume ingredients
from their natural sources can be done in three ways: dry distillation, steam distillation or hydrodiffusion. Dry distillation involves high temperatures, since heat (or
direct flame) is applied to the surface of the vessel containing the plant
material. Usually this technique is reserved for the oils of highest boiling
point, typically those derived from wood, because the high temperatures are
necessary to vaporize their chemical components. Cade and birch tar are the
major oils obtained by dry distillation.
In steam distillation, water or steam
is added to the still pot and the oils are co-distilled with the steam. The oil
is separated from the water by means of a Florentine flask, which separates
them based on their differing densities. The presence of water in the pot
during steam distillation limits the temperature of the process to 100°C. This means that much less degradation occurs in this process
than dry distillation. However, some degradation does occur. For example,
tertiary alcohols present in the plant often dehydrate in the pot and distil as
the corresponding hydrocarbons.
Steam distillation
Hydrodiffusion is a relatively new
technique, and is essentially a form of steam distillation. However, it is
steam distillation carried out upside down since the steam is introduced at the
top of the pot and the water and oil taken off as liquids at the bottom.
Perfume materials obtained this way
are referred to as essential oils, e.g. the oil obtained by steam distillation of lavender is
known as the essential oil of lavender, or lavender oil.