Essential oils are used in a wide variety of consumer goods such as detergents, soaps,
toilet products, cosmetics, pharmaceuticals, perfumes, confectionery food products, soft drinks,
distilled alcoholic beverages (hard drinks) and insecticides. The world production and
consumption of essential oils and perfumes are increasing very fast. Production technology is an
essential element to improve the overall yield and quality of essential oil. The traditional
technologies pertaining to essential oil processing are of great significance and are still being
used in many parts of the globe. Water distillation, water and steam distillation, steam
distillation, cohobation, maceration and enfleurage are the most traditional and commonly used
methods. Maceration is adaptable when oil yield from distillation is poor. Distillation methods
are good for powdered almonds, rose petals and rose blossoms, whereas solvent extraction is
suitable for expensive, delicate and thermally unstable materials like jasmine, tuberose, and
hyacinth. Water distillation is the most favored method of production of citronella oil from plant
material.
Sources of natural essential oil
Essential oils are generally derived from one or more plant parts, such as flowers (e.g.
rose, jasmine, carnation, clove, mimosa, rosemary, lavander), leaves (e.g. mint, Ocimum spp.,
lemongrass, jamrosa), leaves and stems (e.g. geranium, patchouli, petitgrain, verbena,
cinnamon), bark (e.g. cinnamon, cassia, canella), wood (e.g. cedar, sandal, pine), roots (e.g.
angelica, sassafras, vetiver, saussurea, valerian), seeds (e.g fennel, coriander, caraway, dill,
nutmeg), fruits (bergamot, orange, lemon, juniper), rhizomes (e.g. ginger, calamus, curcuma,
orris) and gums or oleoresin exudations (e.g. balsam of Peru, Myroxylon balsamum, storax, myrrh,
benzoin).
Methods of Producing Essential Oils
Regarding hydrodistillation, the essential oils industry has developed terminology to
distinguish three types: water distillation; water and steam distillation; and direct steam
distillation.
Originally introduced by Von Rechenberg, these terms have become established in the
essential oil industry. All three methods are subject to the same theoretical considerations which
deal with distillation of two-phase systems. The differences lie mainly in the methods of
handling the material.
Some volatile oils cannot be distilled without decomposition and thus are usually
obtained by expression (lemon oil, orange oil) or by other mechanical means. In certain
countries, the general method for obtaining citrus oil involves puncturing the oil glands by
rolling the fruit over a trough lined with sharp projections that are long enough to penetrate the
epidermis and pierce the oil glands located within outer portion of the peel (ecuelle method). A
pressing action on the fruit removes the oil from the glands, and a fine spray of water washes the
oil from the mashed peel while the juice is extracted through a central tube that cores the fruit.
The resulting oil-water emulsion is separated by centrifugation. A variation of this process is to
remove the peel from the fruit before the oil is extracted.
Often, the volatile oil content of fresh plant parts (flower petals) is so small that oil
removal is not commercially feasible by the aforementioned methods. In such instances, an
odorless, bland, fixed oil or fat is spread in a thin layer on glass plates. The flower petals are
placed on the fat for a few hours; then repeatedly, the oil petals are removed, and a new layer of
petals is introduced. After the fat has absorbed as much fragrance as possible, the oil may be
removed by extraction with alcohol. This process, known as enfleurage, was formerly used
extensively in the production of perfumes and pomades.
In the perfume industry, most modern essential oil production is accomplished by
extraction, using volatile solvents such as petroleum ether and hexane. The chief advantages of
extraction over distillation is that uniform temperature (usually 50° C) can be maintained during
the process, As a result, extracted oils have a more natural odor that is unmatched by distilled
oils, which may have undergone chemical alteration by the high temperature. This feature is of
considerable importance to the perfume industry; however, the established distillation method is
of lower cost than the extraction process.
Destructive distillation means distilling volatile oil in the absence of air. When wood or
resin of members of the Pinaceae or Cupressaceae is heated without air, decomposition takes
place and a number of volatile compounds are driven off. The residual mass is charcoal. The
condensed volatile matter usually separates into 2 layers: an aqueous layer containing wood
naptha (methyl alcohol) and pyroligneous acid (crude acetic), and a tarry liquid in the form of
pine tar, juniper tar, or other tars, depending on the wood used. This dry distillation is usually
conducted in retorts and, if the wood is chipped or coarsely ground and the heat is applied
rapidly, the yield often represents about 10% of the wood weight used.