How Are Essential Oils Extracted?
Essential oils can be extracted via two key methods:
- Distillation (includes hydro-distillation)
Absolutes, on the other hand, can be extracted via
- Solvent extraction
Carbon-di-oxide extracts are also aromatic in nature,but they differ in chemical structures from their related distilled essential oils.
The Practice of Distillation
Distillation has been practiced from the ancient times. Throughout the early Middle Ages and beyond, a crude form of distillation was known and was primarily used to prepare floral waters or distilled aromatic waters. These techniques have been used in perfumery, digestive tonics, cooking, and for trading.
In 900 AD, Avicenna, the famous child prodigy from Persia who wrote many documents on plants their uses and instructions for massage, was accredited with refining the process of distillation by improving the cooling system.
Today distillation is still the most common process of extracting essential oils from plants. The advantage of distillation is that the volatile components can be distilled at temperatures lower than the boiling points of their individual constituents and are easily separated from the condensed water.
The Distillation Process
For distillation,the plant material is placed upon a grid inside the still. Once inside, the still is sealed, and, depending upon the above methods, steam or water/steam slowly breaks through the plant material to remove its volatile constituents and extract essential oils. These volatile constituents float in the upward direction, through a connecting pipe that leads them into a condenser. The condenser cools the rising vapor back into its liquid form. This liquid is then collected in a vehicle below the condenser. Since water and essential oils do not mix, essential oil can be found floating on the surface of the water where it is siphoned off. In exceptional cases like clove essential oil, oil is heavier than water and is found on the bottom of the condenser.
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The Three Types of Distillation
Water Distillation : The plant material comes into direct contact with water. This method is generally used with flowers (rose and orange blossoms), as direct steam causes these flowers to clump together making it difficult for steam to pass through.
Water and Steam : This method can be used with herb and leaf material. During this process, water remains below the plant material, which has been placed on a grate while steam is introduced from outside.
Steam Distillation : This method is the most commonly used method. During this process, steam is injected into the still, usually at slightly higher pressures and temperatures than the above two methods.
Boiling point is the temperature at which liquid is converted to gas at a specified pressure. The fundamental nature of steam distillation is that it enables a compound or a mixture of compounds to be distilled (and subsequently recovered) at a temperature substantially below than that of the individual constituent(s). Essential oils contain substances with boiling points up to 200°C or higher, including some that are solids at normal temperatures. In the presence of steam or boiling water, these substances get volatilized at a temperature close to 100°C.
Percolation or Hydro-Diffusion
This is a relatively recent method and is very similar to steam distillation with an exception that steam comes in through the top rather than the bottom of the condenser, thus a shorter distillation time. It is useful in extracting essential oils from woody or tough materials and seeds such as fennel or dill.
Hydrosols : A By-product of Distillation
Hydrosols, also known as hydrolats, are the by-product or product (depending on the distiller purpose) of the distillation process. Hydrosols contain water-soluble constituents of aromatic plants and retain a small amount of essential oil. Every liter of hydrosol contains 0.05 – 0.2 milliliter of dissolved essential oil, depending on the water solubility of the plant’s components and the distillation parameters.
When water and essential oils are mixed together with or without a dispersant, this is called a “spritzer” or “aromatic spritzer,” and this product should not be confused with a true hydrosol.
Expression, also referred to as cold pressing, is a method of extraction specific to citrus essential oils, such as tangerine, lemon, bergamot, sweet orange and lime. In older times, expression was done in the form of sponge pressing, which was literally accomplished by hand. The zest or rind of citrus would first be soaked in warm water to make the rind more receptive to the pressing process. A sponge would then be used to press the rind, thus breaking the essential oil cavities, and absorb the essential oils. Once the sponge is filled with the extracted juice, it would then be pressed over a collecting container.It is then made to stand for the separation of essential oils from water/juice. The essential oil is finally siphoned off.
A more modern method of extraction, and less labor-intensive technique, termed as ecuelle a piquer process involves prodding, pricking and sticking action to release the essential oils. During this process, rind of the fruit is placed in a container having spikes that puncture the peel while the device is rotated. The puncturing of rind will release the essential oils which is then collected in a small area below the container. The end process is the same as above. Majority of modern expression techniques are accomplished through machines using centrifugal force. Spinning in a centrifuge separates majority of essential oils from the fruit juice.
What is the difference between expressed and distilled Citrus Oils?
Expressed citrus oils are produced by mechanical separation (cold pressing) of oil from the peels of various citrus fruits such as orange, grapefruit, tangerine, lemon, lime, petitgrain and bergamot. Expressed citrus oils contain small amounts of naturally occurring non-volatile residues such as waxes.
Citrus oils can also be distilled from peels or whole fruits as well. Even though its aroma differs from expressed citrus oils, its distilled versions offer certain advantages like:
1) Distilled citrus oils do not contain nonvolatile residues which can clog diff-users, stain fabric, and shorten the shelf life.
2) Distilled citrus oils don’t contain nonvolatile furocoumarins and are generally less photo sensitizing .
Flowers were being processed via enfleurage in the Grasse region of Southern France long before the modern methods of solvent extraction were discovered. In the early days of perfumery, many flower scents were extracted via enfleurage. Enfleurage is now considered an ancient art that is passed down from father to son, from generation to generation.
Enfleurage is a cold-fat extraction process that is based upon the principle that fat has a high power of absorption, particularly animal fat.It is a method used for flowers that continue developing and giving off their aroma even after harvesting (e.g., jasmine and tuberose).
Today, Grasse continues to be one of the few areas in the world that continues to employ enfleurage as a method of extraction.Although it is expensive,it is used in aromatherapy market.
Some plant material is too fragile to be distilled and an alternative method must be employed to extract its essential oils. Solvent extraction is the use of solvents, such as petroleum ether, methanol, ethanol, or hexane, to extract the odoriferous lipophilic material from the plant. The solvent will also pull out chlorophyll and other plant tissues, which will give us a highly colored or thick/viscous extract. The first product made via solvent extraction is known as a concrete. Concrete is the concentrated extract that contains waxes and/or fats as well as the odoriferous materials from the plant. This concrete is then mixed with alcohol,which leads to the formation of absolute as the final product.
Solvent extraction is used for extraction of essential oils from jasmine, tuberose, carnation, gardenia, jonquil, violet leaf, narcissus, mimosa, and other delicate flowers. Neroli and rose can be distilled or solvent-extracted.
Absolutes do have therapeutic values and are often used for psychological purposes. Many therapists incorporate absolutes, such as rose absolute, jasmine, and tuberose, for therapeutic applications of aromatherapy.
Absolutes are highly concentrated aromatic substances and are obtained from delicate flowers by either enfleurage or solvent extraction. Absolutes will most often resemble the natural aroma of the plant and are normally more colored and viscous than essential oils. Absolutes are used extensively used in the cosmetic and perfume industries due to their strong aromas. There are different grades of absolutes found in the market. The top grade absolutes are uncut, and can be a thick or semi-solid substance, making them difficult to use. Less expensive grades are diluted with alcohol to make them more user friendly.Often the strength of aroma is slightly diminished than high grade absolutes.
Carbon-di-oxide Hypercritical Extraction
Hypercritical carbon dioxide extraction is a relatively new process used for the extraction of aromatic products. The basic concept of hypercritical carbondioxide extraction is that carbondioxide will turn from a gas into a liquid under pressure.This liquid can now be used as an inert liquid solvent. This liquid solvent is able to diffuse throughout the plant,thus extracting its aromatic constituents. Carbon-di-oxide extracts contain most of the same constituents as their essential oil counterparts.They can contain some elements not found in essential oils as well.
The three main disadvantages of this process are
- Potential Pesticide Residue,
- Lack of information regarding their safety and therapeutic benefits.