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Aromatherapy Extracts Produced from Plants

Distillation

Historical Distillation of Plants, Oils and Waters

Historical texts vary in their accounts of the types of distillation practiced in the past, but one fact remains; distillation of plants has been around for a very long time, albeit not always in the form that we are familiar with today.

Distillation, in its crudest form, is defined by Encyclopedia Britannica as a, “…process involving the conversion of a liquid into vapour that is subsequently condensed back to liquid form.”1 However, as any experienced distiller will tell you, distillation is not only a scientific process but a true art as well.

Plants are placed in the still, through either water or steam distillation (see The Process of Distillation below) and transformed from plant to steam to liquid through a complex system of managing plant matter, heat, and water. The end result produces either an essential oil or hydrosol.

We may never know the exact process of how early civilizations turned plants into oils and hydrosols, but an interesting paper on the Early History of Distillation by T. Fairley, F.R.S.E., F.I.C, from 1906 discusses various methods of distillation practiced by ancient people of India, Arabia, China, Phoenicia, Greece, and Rome.2 Indeed, Ann Harman in her book Harvest to Hydrosol states that: “The oldest [alembic] still that has been discovered, to date, is almost 4000 years old.”3 The still which she is talking about was found by Dr. Maria Rosaria Belgiorno at Pyrgos in 2005.

Most historical texts agree that the ancient Egyptians were using plants as oils for perfumery and medicinal practice, as well as religious purposes. Scent was revered by the ancient Egyptians as a key to everlasting life. Aromatic oils and plants were used in all aspects of daily life.4 The ancient Greeks and Romans then learned techniques and use of plants and oils from the Egyptians. However, it was a physician from Persia by the name of Avicenna (980 A.D. – 1037 A.D.) who made a significant contribution to how plants are distilled today; the addition of the refrigerated coil into the still.5

Methods of Extraction

The two most common forms of distillation of both essential oils and hydrosol are steam distillation and water (hydro) distillation. The primary difference between these methods is that with water distillation the plant material is based within the water and with steam distillation the plant material is based above the water. Sometimes a distiller may perform a combo-distillation which is essentially a combination of both methods of extraction.

The distillation process for essential oils and hydrosols is broken down as follows:

  • Plant material (for example leaves, flowers, twigs, or seeds) is placed in a vat (either in the water itself of on a screen in which steam passes through).
  • Heat is applied underneath the vat.
  • The essential oil molecules from the plant material “escape from the plant” and evaporate into steam which is forced along a pipe.
  • The pipe passes through a cold-water vat and, as the steam cools, the essential oil molecules turn into liquid –the essential oil. Essential oil molecules will either “sink” or “float” on the water, which means that they can easily be separated from the water to be used as an essential oil. Conversely, the water can be drained off to be used as a hydrosol.

Expression

Expression is the method of extraction used to extract essential oils from citrus fruits such as lemon (Citrus x limon), sweet orange (Citrus sinensis), lime (Citrus aurantifolia), and grapefruit (Citrus x paradisi). This method is also called cold pressing as there is little to no heat used in the process. Expressed essential oils are composed chemically the same as when they existed in the plant. They contain natural waxes.

Expressed essential oils are collected by centrifugation using equipment such as a pelatrice or sfumatrice. The pelatrice method involves rotating the citrus fruits against the rough shell of the machine which subsequently pierces the rind to release the essential oil. Further processing gathers any remaining essential oil and a separator ensures that the end result is simply essential oil. The sfumatrice method draws rollers with metal chains over the rinds of the fruit to release the essential oil. Again, a separator cleans everything up to produce a true essential oil end product.6

Video of a modern extraction of citrus essential oil.

Some citrus essential oils can also be obtained via distillation. The main advantage of distilled citrus essential oils is that the majority of them are not phototoxic as the presence of furocoumarins is removed. However, they may be slightly chemically and therapeutically different to the expressed oil from the same fruit.

Note: Please see NAHA’s safety page for more information on photosensitizing essential oils: http://www.naha.org/explore-aromatherapy/safety/


Extraction Techniques for Absolutes & CO2 Extracts

Enfleurage

 

Enfleurage is a labor-intensive process that was traditionally used to make perfumes. It was used a lot in Grasse, France, the traditional perfume capital of the world for fragile flower blooms, such as jasmine (Jasminum grandiflorum) and tuberose (Polianthes tuberosa).

Flowers were hand-picked at sunrise, throughout the day, or at sunset, depending upon the species of flower. Flowers were then left to macerate in oils and animal fat over a number of days or weeks. The idea was that the fat would absorb the aroma of these difficult-to-extract flowers. Because enfleurage is such a labor-intensive method of plant extraction, it is little used today commercially and the process of solvent extraction has replaced it.

Solvent Extraction

Some plants are difficult to process. A different method might be used to extract the aroma from these types of plants. However, these processes use a chemical base. The resulting product is known as an absolute, concrete, resin, resinoid, or oleoresin. These substances are usually thicker in nature than a true essential oil and the aroma can be different. Perfumists often use these types of extracts as they are extremely aromatic. However, aromatherapists can often use them in place of the essential oil, particularly for emotional work.

Some of these plants can also be distilled or extracted by carbon dioxide. Check carefully which type of extract you are using. Retailers should make it clear on the label of the bottle you are purchasing but if in doubt, ask. A reputable supplier should be able to answer your questions confidently.

Concretes are prepared from plant material using a hydrocarbon solvent to produce a waxy, solid substance. Absolutes are prepared from concretes by alcohol extraction. Examples of concretes and absolutes include gardenia (Gardenia jasminoides), violet (Viola odorata), and narcissus (Narcissus poeticus). Note that jasmine (Jasminum grandiflora) is steam distilled from the absolute, not the plant itself. Some plants, such as rose (Rosa x damascena) may produce an essential oil, concrete, and absolute. The final product differs in aroma and, to some extent, therapeutic properties.

Resins are the natural material (gum) exuded from the bark of a tree when it is cut. Resinoids are the result of a resin extraction by use of a hydrocarbon solvent. Absolute resins are also produced using an alcohol solvent. Oleoresins are the natural material exuded from plants and are extracted using a solvent. Oleoresins both essential oils and resins (and solvents).

Plants which produce a resinoid include opopanax (Commiphora erythraea) and myrrh (Commiphora myrrha). Both of these plants also produce an essential oil. Nutmeg (Myristica fragrans) produces an oleoresin from mace. Benzoin (Styrax benzoin) produces an absolute resin (or resinoid).

Carbon Dioxide (CO2)

Carbon dioxide (CO2) extracted oils have risen in recent years. Often plants that could not be distilled in the past are being extracted by the CO2 method. In addition, plants that are distilled can also be extracted via the CO2 method, producing products with different aromas and sometimes therapeutic properties.

CO2 extraction uses both high and low pressure to extract essential oils from plants. Temperatures range between 95 to 100F compared to 140 to 212F used in the steam distillation method. This produces an essential oil with a different chemical composition to a steam distilled essential oil.

CO2 extracted products can be either CO2 select or CO2 total; CO2 select are produced using low pressure where CO2 total are produced using high pressure.

Infused Oils

Infused oils (also called macerated oils) are made from plant material immersed in a vegetable oil base such as sunflower (Helianthus annuus). Plant material is chopped, added, and left to agitate for several days. It should be placed in a sunny window. Eventually, the plant material is filtered out to leave a vegetable oil made up of the base oil’s and plant’s therapeutic properties.

Examples of infused oils include calendula (Calendula officinalis) and St John’s wort (Hypericum perforatum). However, many herbal plants can be infused, in addition to resins.

 


References

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