Expression or cold pressing, as it is also known, is only used in the production of citrus
peel are crushed or broken to release the oil. One method that was practiced many years ago,
particularly in Sicily (spugna method), commenced with halving the citrus fruit followed by pulp
removal with the aid of sharpened spoon-knife (known as a rastrello). The oil was removed from
the peel either by pressing the peel against a hard object of baked clay (concolina) which was
placed under a large natural sponge or by bending the peel into the sponge. The oil emulsion
absorbed by the sponge was removed by squeezing it into the concolina or some other container.
It is reported that oil produced this way contains more of the fruit odor character than oil
produced by any other method.
A second method known as equaling (or the scodella method), uses a shallow bowl of
copper (or sometimes brass) with a hollow central tube; the equaling tool is similar in shape to a
shallow funnel. The bowl is equipped with brass points with blunt ends across which the whole
citrus fruit is rolled by hand with some pressure until all of the oil glands have burst. The oil and
aqueous cell contents are allowed to dribble down the hollow tube into a container from which
the oil is separated by decantation.
Obviously, hand pressing is impractical because it is an extremely slow process, e.g. on
average only 2-4 lbs oil per day can be produced by a single person using one of these hand
methods. As a result, over the years a number of machines have been designed to either crush the
peel of a citrus fruit or crush the whole fruit and then separate the oil from the juice.
Pelatrice Process
In the pelatrice process, citrus fruits are fed from a hopper into the abrasive shell of the
machine. The fruits are rotated against the abrasive shell by a slow-moving Archimedian screw
whose surface rasps the fruit surfaces causing some of the essential oil cavities on the peel to
burst and release their oil-water emulsion. This screw further transports the fruit into a hopper in
which rollers covered with abrasive spikes burst the remaining oil cavities. The oil and water
emulsion is washed away from the fruit by a fine spray of water. The emulsion next passes
through a separator where any solids are removed, after which it passes through two centrifugal
separators working in series to yield the pure oil. Most bergamot oil and some lemon oil are produced this way in Italy.
Sfumatrice Process
The sfumatrice equipment consists of a metallic chain that is drawn by two horizontal
ribbed rollers. The peels are conveyed through these rollers during which time they are pressed
and bent to release their oil. As in pelatrice, the oil is washed away from the sfumatrice rollers
by fi ne sprays of water. Again, the oil is initially passed through a separator prior to being sent
to two centrifuges in series, so that purified oil can be produced. At one time, sfumatrice was the
most popular process for citrus oil isolation in Italy; however, today the pelatrice method
appears more popular.
Essential Oil Extraction with Cold Fat (Enfleurage)
Despite the introduction of the modern process of extraction with volatile solvents, the
old fashioned method of enfleurage, as passed on from father to son and perfected in the course
of generations, still plays an important role. Enfleurage on a large scale is today carried out only
in the Grasse region of France, with the possible exception of isolated instances in India where
the process has remained primitive.
The principles of enfleurage are simple. Certain flowers (e.g. tuberose and jasmine)
continue the physiological activities of developing and giving off perfume even after picking.
Every jasmine and tuberose flower resembles, so to speak, a tiny factory continually emitting
minute quantities of perfume. Fat possesses a high power of absorption and, when brought in
contact with fragrant flowers, readily absorbs the perfume emitted. This principle, methodically
applied on a large scale, constitutes enfleurage. During the entire period of harvest, which lasts
for eight to ten weeks, batches of freshly picked flowers are strewn over the surface of a
specially prepared fat base (corps), let there (for 24 h in the case of jasmine and longer in the
case of tuberose), and then replaced by fresh flowers. At the end of the harvest, the fat, which is
not renewed during the process, is saturated with flower oil. Thereafter, the oil is extracted from
the fat with alcohol and then isolated.
The success of enfleurage depends to a great extent upon the quality of the fat base
employed. Utmost care must be exercised when preparing the corps. It must be practically
odorless and of proper consistency. If the corps is too hard, the blossoms will not have sufficient
contact with the fat, curtailing its power of absorption and resulting in a subnormal yield of
flower oil. On the other, if it is too soft, it will tend to engulf the flowers and the exhausted ones
will adhere; when removed, the flowers will retain adhering fat, resulting in considerable
shrinkage and loss of corps. The consistency of the corps must, therefore, be such that it offers a
semihard surface from which the exhausted flowers can easily be removed. The process of
enfleurage is carried out in cool cellars, and every manufacturer must prepare the corps
according to the prevailing temperature in the cellars during the months of the flower harvest.
Many years of experience have proved that a mixture of one part of highly purified tallow
and two parts of lard is eminently suitable for enfleurage. This mixture assures a suitable
consistency of the corps in conjunction with high power of absorption. The fat corps thus
prepared is white, smooth, absolutely of uniform consistency, free of water and practically
odorless. Some manufacturers also add small quantities of orange flower or rose water when
preparing the corps. This seems to be done for the sake of convention. Such additions somewhat
shade the odor of the finished product by imparting a slight orange blossom or rose note.
Enfleurage and Defleurage
Every enfleurage building is equipped with thousands of socalled chassis, which serve as
vehicles for holding the fat corps during the process. A chassis consists of a rectangular wooden
frame. The frame holds a glass plate upon both sides of which the fat corps is applied with a
spatula at the beginning of the enfleurage process. When piled one above the other, the chassis
form airtight compartments, with a layer of fat on the upper and lower side of each glass plate.
Every morning during the harvest the freshly picked flowers arrive, and after being cleaned of
impurities, such as leaves and stalks, are strewn by hand on top of the fat layer of each glass
plate. Blossoms wet from dew or rain must never be employed, as any trace of moisture will turn
the corps rancid. The chassis are then piled up and left in the cellars for 24 h or longer,
depending upon the type of flowers. The latter rest in direct contact with one fat layer (the lower
one), which acts as a direct solvent whereas the other fat layer (beneath the glass plate of the
chassis above) absorbs only the volatile perfume given off by the flowers.
After 24 h, the flowers have emitted most of their oil and start to wither, developing an
objectionable odor. They must then be removed from the corps, which process, despite all efforts
to introduce labor-saving devices, is still done by hand. Careful removal of the flower
(defleurage) is almost more important than charging the corps on the chassis with fresh flowers
(enfleurage) and, therefore, the persons doing this work must be experienced and skilled. Most of
the exhausted flowers will fall from the fat layer on the chassis glass plate when the chassis is
struck lightly against the working table, but since it is necessary to remove every single flower
and every particle of the flower, tweezers are used for this delicate operation.
Immediately following defleurage, that is, every 24 h, the chassis are recharged with
fresh flowers. For this purpose the chassis are turned over and the fat layer, which in the previous
operation formed the top (ceiling) of the small chamber, is now directly charged with flowers. In
the case of jasmine, the entire enfleurage process lasts about 70 days: daily the exhausted flowers
are removed and the chassis are recharged with fresh ones. At the beginning of, and several times
during, the harvest, the fat on the chassis is scratched over with metal combs and tiny furrows are
drawn in order change and increase the surface of absorption.
At the end of the harvest, the fat is relatively saturated with flower oil and possesses the
typical fragrance. The perfumed fat must then be removed from the glass plates between the
chassis. For this purpose, it is scraped off with a spatula and then carefully melted and bulked in
closed containers. The final product is called pomade (pomade de jasmine, pomade de tuberous,
pomade de violet, etc.). The most highly saturated pomade is pomade no. 36, because the corps
on the chassis have been treated with fresh flowers 36 times during the whole process of
enfleurage.
At the beginning of the harvest, every chassis is charged with about 360 g fat corps on
each side of the glass plate, in other words, with 720 g per chassis. Every kilogram of fat corps
should be in contact with about 2.5 kg (preferably with 3.0 kg) of jasmine flowers for the entire
period of enfleurage, which lasts from 8 to 10 weeks. The quantities differ somewhat for
different flowers. At the end of enfleurage, the fat corps has lost about 10% of its weight because
of the various manipulations.
In this process, the long enfleurage time is reduced by the immersion of petals in molten
fat heated at 45°-60° C for 1 to 2 h, depending upon the plant species. After each immersion, the
fat is filtered and separated from the petals. After 10 to 20 immersions, the fat is separated from
waste flowers and water. Absolute of maceration is then produced from fat containing oil
through the process of extraction and concentration under reduced pressure. It is mainly used for
highly delicate flowers whose physiological activities are lost rapidly after their harvest, such as
lily of valley.
Modern (Non-traditional) Methods of Extraction of Essential Oils
Traditional methods of extraction of essential oils have been discussed and these are the
methods most widely used on commercial scale. However, with technological advancement, new
techniques have been developed which may not necessarily be widely used for commercial
production of essential oils but are considered valuable in certain situations, such as the
production of costly essential oils in a natural state without any alteration of their
thermosensitive components or the extraction of essential oils for micro-analysis. These
techniques are as follows:
• Headspace trapping techniques
– Static headspace technique
– Vacuum headspace technique
– Dynamic headspace technique
• Solid phase micro-extraction (SPME)
• Supercritical fluid extraction (SFE)
• Phytosol (phytol) extraction
• Protoplast technique
• Simultaneous distillation extraction (SDE)
• Microwave distillation
• Controlled instantaneous decomposition (CID)
• Thermomicrodistillation
• Microdistillation
• Molecular spinning band distillation
• Membrane extraction
Some of these techniques are discussed in other chapters. Here, a few important, relevant
references are provided.
Conclusions
Some of the major constraints in sustainable industrial exploitation of medicinal and
aromatic plants (MAPs) are due to the fact that the countries of South East Asia have poor
agricultural practices for MAPs, unscientific and indiscriminate gathering practices from the
wild, poor postharvest and post-gathering practices leading to poor quality raw material, lack of
research for the development of high-yielding varieties of MAPs, poor propagation methods,
inefficient processing techniques, poor quality control procedures, lack of research on process
and product development, difficulty in marketing, non-availability of trained personnel, lack of
facilities and tools to fabricate equipment locally, and finally lack of access to the latest
technologies and market information. This calls for co-operation and coordination among various
institutes and organizations of the region, in order to develop MAPs for sustainable commercial
exploitation.
The process of extracting MAPs determines how efficiently we add value to MAP
bioresources. In the case of essential oils, the extraction process affects the physical as well as
internal composition. External appearance, at times, can result in rejection of the batch even if
the analytical results are within acceptable limits. Furthermore, essential oils are evaluated
internationally for their olfactory properties by experienced perfumers and these olfactory
qualities supersede analytical results. Variations in the chemical constituents of the extracts of
medicinal plants may result by using non-standardized procedures of extraction. Efforts should
be made to produce batches with quality as consistent as possible (within the narrowest possible
range).