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Aromatic Extraction Techniques in Perfumery
Before perfumed products can be composed, the odorants used in the various perfume compositions must first be obtained. Synthetic odorants are produced through organic synthesis. The term "aroma extraction" refers to the extraction of aromatic compounds from raw natural plant materials, using methods such as distillation, solvent extraction, expression, or enfleurage. The results of the extraction are essential oils, absolutes, concretes, or butters, depending on the amount of waxes in the extracted product. The different methods have been devised to make the extracted material smell as much like the donor plant as possible and to be cost-effective. To a certain extent all of these procedures are damaging: they denature the aromatic compounds, changing their odor profile or even making them totally odorless. This has to do with the materials themselves having so little volatile oil that they do not yield a sufficient crop (lily of the valley and gardenia, for example) or being too delicate to withstand techniques that employ heat, harsh solvents, or exposure to oxygen.
Commercial Extraction Processes
EXPRESSION
Expression is among the oldest methods of fragrance extraction. Aromatic essential oil is produced from plants that are squeezed or compressed, forcing the complete oil out. These oils were first produced in Egypt in unglazed ceramic vases, with the flowers pressed and then buried in the desert for driving out the moisture. The water has a smaller molecular size, so it diffuses through the ceramic vessels, while the larger essential oils do not. The lotus oil in Tutankhamen's tomb, which retained its scent after 3000 years sealed in alabaster vessels, was pressed in this manner. Expression is an especially mild process, historically used in cases where steam distillation would modify or damage the end product. Today the only oils obtained by expression are those from the rinds of citrus fruits, due both to the abundance of aromatics in this squeezable part of the fruit and to the low cost of growing citrus fruits in general. This method is sometimes called cold pressure extraction.
DISTILLATION
Distillation, using an alembic (an alchemical still consisting of two vessels connected by a tube), is an advanced method developed in the Middle Ages and is now a common one, used for rendering a variety of aromatic essences, with the raw material sources being wood, bark, roots, flowers, leaves, seeds, peels, and flowers. In this procedure, a carrier solvent (usually water but sometimes another liquid such as alcohol) is boiled and its steam is passed through the raw material in the still for 60-100 minutes, taking the fragrant substances along with it. After cooling and condensing of the vapor, the essential oil, which floats to the top, is separated from the distillation water in Florentine flasks. The resulting material is still mostly called an essential oil, comprising aromatic and volatile ingredients of the raw material. Several very common essential oils such as peppermint, basil, lavender, rose, palmarosa, geranium, sandalwood, and eucalyptus, are produced in this way. Distillation produces different quality grades of essential oils, making some finer than others. The water collected from the condensate, which retains some of the fragrant compounds from the raw material after the oil is removed, is called hydrosol and is also sometimes sold. Examples are rose hydrosols and orange blossom hydrosols.
Rectification (also called dry or destructive distillation): The raw materials are directly heated in a still, without a carrier solvent such as water or alcohol, and often in the absence of air. Fragrant compounds that are released from the raw material by the high heat undergo anhydrous pyrolysis, which results in the formation of different compounds and thus different fragrance notes that can be used in perfume compositions. This method is used to obtain fragrant compounds from fossil amber and fragrant woods, where an intentional "burned" or "toasted" phenolic (tar-like) odor is desired. Examples are birch tar oil and Styrax pyrogenated oil.
Fractional distillation: A prolonged process is used, employing a fractionating column, which renders several grades of the aromatic compound, varying in quality and depth of scent. This allows for greater control of the qualities of the end material produced and is therefore very helpful in allowing manipulation of the effects they have in a fragrance formula. Although the product of fractional distillation is more expensive, this process is sometimes necessary to remove unpleasant or undesirable scents of a material. It is commonly used for ylang-ylang.
SOLVENT EXTRACTION/MACERATION
Organic solvent extraction is the most common and most economically important technique for extracting aromatics in the modern perfume industry. Raw materials are submerged in a solvent that can dissolve the desired aromatic compounds. Commonly used solvents for maceration/solvent extraction include hexane, ethane, and dimethyl ether.
Fragrant compounds from woody and fibrous plant materials are often obtained in this way, as are all aromatics from animal sources (although this is increasingly uncommon due to ethical concerns). The technique can also be used to extract odorants that are too volatile for distillation or are easily denatured by heat. The remaining waxy mass is known as a concrete, which is a mixture of essential oil, waxes, resins, and other lipophilic (oil-soluble) plant material. Although highly fragrant, concretes are too viscous - sometimes even solid - at room temperature to be useful. This is due to the presence of high-molecular-weight, nonfragrant waxes and resins. Another solvent, often ethanol (ethyl alcohol), which only dissolves the fragrant low-molecular-weight compounds, must be used to extract the fragrant oil from the concrete. The alcohol is removed by a second distillation, leaving behind what is called the absolute. Due to the lower temperatures used in this process, the absolute can be more faithful to the original scent of the raw material than are the products of distillation.
Supercritical fluid extraction: In supercritical fluid extraction, a relatively new method, high pressure carbon dioxide gas (up to 100 atm) is used as a solvent. When carbon dioxide is put under high pressure at slightly above room temperature, a supercritical fluid forms. (Under normal pressure, CO2 changes directly from a solid to a gas in a process known as sublimation.) CO2 in a non-polar compound has low surface tension and wets easily, and it can be used to extract the typically hydrophobic aromatics from the plant material. This process is identical to one of the techniques for making decaffeinated coffee. Like solvent extraction, CO2 extraction takes place at a low temperature, extracts a wide range of compounds, and leaves the aromatics unaltered by heat, producing an essence that is very faithful to the original. Since CO2 is a gas at normal atmospheric pressure, it also leaves no trace of itself in the final product, thus allowing one to get the absolute directly without having to deal with a concrete. Extracts produced using this process are known as CO2 extracts.
INFUSION
Water maceration produces an infusion, a familiar term from tisanes/herbal teas and a comparable technique. The plant material is submerged in hot water (or alcohol or oil) and left to marinate (steep) for a period of time, yielding its aromatic properties. Then the plant is removed with a strainer and the water remaining is called an infusion. The process of infusion is distinct from decoction, which involves boiling the plant material, or percolation, in which the water passes through the material (as in a coffeemaker). Infusion is a very simple chemical process used with botanicals that are highly volatile and dissolve readily or release their active ingredients easily in the liquid. The botanicals are typically dried herbs, flowers or berries.
DECOCTION
Decoction is a method of extraction by boiling out dissolved chemicals from mashed plant material, which may include stems, roots, bark, and rhizomes. Decoction produces liquids with differing chemical properties than those of infusion because the temperature/preparation difference results in more oil-soluble chemicals in decoction than in infusion. Decoction is also the name for the resulting liquid.
ENFLEURAGE
Enfleurage is a famous but now antiquated process, prized in years past for its capacity to capture the mature, deep aroma of delicate flowers, such as jasmine or tuberose, that lost their precious aromatic bouquet in high-heat distillation. Enfleurage in the original French means to “impregnate with the scent of flowers.†It is also defined as “extracting perfumes by exposing inodorous oils or fats to the exhalations of flowers.â€
The technique uses animal fat (deodorized lard or tallow) as a waxy 'dress' for the flowers, allowing them to macerate for days on large glass plates in wooden frames. Fresh produce was added to the point of fragrance saturation. The fragrant fat 'pomade' was then washed with ethanol to render an 'absolute de chassis.' Two variations of the technique existed: 'cold' enfleurage, perfected in the 19th century and using no external heat, and 'hot' enfleurage, in which the fat was gently heated while the botanical matter was stirred into the fat.
This technique is not commonly used any longer in the perfume industry, due both to its prohibitive labor intensity and cost and to the existence of newer, more efficient extraction methods such as solvent extract and supercritical fluid extraction.
Before perfumed products can be composed, the odorants used in the various perfume compositions must first be obtained. Synthetic odorants are produced through organic synthesis. The term "aroma extraction" refers to the extraction of aromatic compounds from raw natural plant materials, using methods such as distillation, solvent extraction, expression, or enfleurage. The results of the extraction are essential oils, absolutes, concretes, or butters, depending on the amount of waxes in the extracted product. The different methods have been devised to make the extracted material smell as much like the donor plant as possible and to be cost-effective. To a certain extent all of these procedures are damaging: they denature the aromatic compounds, changing their odor profile or even making them totally odorless. This has to do with the materials themselves having so little volatile oil that they do not yield a sufficient crop (lily of the valley and gardenia, for example) or being too delicate to withstand techniques that employ heat, harsh solvents, or exposure to oxygen.
Commercial Extraction Processes
EXPRESSION
Expression is among the oldest methods of fragrance extraction. Aromatic essential oil is produced from plants that are squeezed or compressed, forcing the complete oil out. These oils were first produced in Egypt in unglazed ceramic vases, with the flowers pressed and then buried in the desert for driving out the moisture. The water has a smaller molecular size, so it diffuses through the ceramic vessels, while the larger essential oils do not. The lotus oil in Tutankhamen's tomb, which retained its scent after 3000 years sealed in alabaster vessels, was pressed in this manner. Expression is an especially mild process, historically used in cases where steam distillation would modify or damage the end product. Today the only oils obtained by expression are those from the rinds of citrus fruits, due both to the abundance of aromatics in this squeezable part of the fruit and to the low cost of growing citrus fruits in general. This method is sometimes called cold pressure extraction.
DISTILLATION
Distillation, using an alembic (an alchemical still consisting of two vessels connected by a tube), is an advanced method developed in the Middle Ages and is now a common one, used for rendering a variety of aromatic essences, with the raw material sources being wood, bark, roots, flowers, leaves, seeds, peels, and flowers. In this procedure, a carrier solvent (usually water but sometimes another liquid such as alcohol) is boiled and its steam is passed through the raw material in the still for 60-100 minutes, taking the fragrant substances along with it. After cooling and condensing of the vapor, the essential oil, which floats to the top, is separated from the distillation water in Florentine flasks. The resulting material is still mostly called an essential oil, comprising aromatic and volatile ingredients of the raw material. Several very common essential oils such as peppermint, basil, lavender, rose, palmarosa, geranium, sandalwood, and eucalyptus, are produced in this way. Distillation produces different quality grades of essential oils, making some finer than others. The water collected from the condensate, which retains some of the fragrant compounds from the raw material after the oil is removed, is called hydrosol and is also sometimes sold. Examples are rose hydrosols and orange blossom hydrosols.
Rectification (also called dry or destructive distillation): The raw materials are directly heated in a still, without a carrier solvent such as water or alcohol, and often in the absence of air. Fragrant compounds that are released from the raw material by the high heat undergo anhydrous pyrolysis, which results in the formation of different compounds and thus different fragrance notes that can be used in perfume compositions. This method is used to obtain fragrant compounds from fossil amber and fragrant woods, where an intentional "burned" or "toasted" phenolic (tar-like) odor is desired. Examples are birch tar oil and Styrax pyrogenated oil.
Fractional distillation: A prolonged process is used, employing a fractionating column, which renders several grades of the aromatic compound, varying in quality and depth of scent. This allows for greater control of the qualities of the end material produced and is therefore very helpful in allowing manipulation of the effects they have in a fragrance formula. Although the product of fractional distillation is more expensive, this process is sometimes necessary to remove unpleasant or undesirable scents of a material. It is commonly used for ylang-ylang.
SOLVENT EXTRACTION/MACERATION
Organic solvent extraction is the most common and most economically important technique for extracting aromatics in the modern perfume industry. Raw materials are submerged in a solvent that can dissolve the desired aromatic compounds. Commonly used solvents for maceration/solvent extraction include hexane, ethane, and dimethyl ether.
Fragrant compounds from woody and fibrous plant materials are often obtained in this way, as are all aromatics from animal sources (although this is increasingly uncommon due to ethical concerns). The technique can also be used to extract odorants that are too volatile for distillation or are easily denatured by heat. The remaining waxy mass is known as a concrete, which is a mixture of essential oil, waxes, resins, and other lipophilic (oil-soluble) plant material. Although highly fragrant, concretes are too viscous - sometimes even solid - at room temperature to be useful. This is due to the presence of high-molecular-weight, nonfragrant waxes and resins. Another solvent, often ethanol (ethyl alcohol), which only dissolves the fragrant low-molecular-weight compounds, must be used to extract the fragrant oil from the concrete. The alcohol is removed by a second distillation, leaving behind what is called the absolute. Due to the lower temperatures used in this process, the absolute can be more faithful to the original scent of the raw material than are the products of distillation.
Supercritical fluid extraction: In supercritical fluid extraction, a relatively new method, high pressure carbon dioxide gas (up to 100 atm) is used as a solvent. When carbon dioxide is put under high pressure at slightly above room temperature, a supercritical fluid forms. (Under normal pressure, CO2 changes directly from a solid to a gas in a process known as sublimation.) CO2 in a non-polar compound has low surface tension and wets easily, and it can be used to extract the typically hydrophobic aromatics from the plant material. This process is identical to one of the techniques for making decaffeinated coffee. Like solvent extraction, CO2 extraction takes place at a low temperature, extracts a wide range of compounds, and leaves the aromatics unaltered by heat, producing an essence that is very faithful to the original. Since CO2 is a gas at normal atmospheric pressure, it also leaves no trace of itself in the final product, thus allowing one to get the absolute directly without having to deal with a concrete. Extracts produced using this process are known as CO2 extracts.
INFUSION
Water maceration produces an infusion, a familiar term from tisanes/herbal teas and a comparable technique. The plant material is submerged in hot water (or alcohol or oil) and left to marinate (steep) for a period of time, yielding its aromatic properties. Then the plant is removed with a strainer and the water remaining is called an infusion. The process of infusion is distinct from decoction, which involves boiling the plant material, or percolation, in which the water passes through the material (as in a coffeemaker). Infusion is a very simple chemical process used with botanicals that are highly volatile and dissolve readily or release their active ingredients easily in the liquid. The botanicals are typically dried herbs, flowers or berries.
DECOCTION
Decoction is a method of extraction by boiling out dissolved chemicals from mashed plant material, which may include stems, roots, bark, and rhizomes. Decoction produces liquids with differing chemical properties than those of infusion because the temperature/preparation difference results in more oil-soluble chemicals in decoction than in infusion. Decoction is also the name for the resulting liquid.
ENFLEURAGE
Enfleurage is a famous but now antiquated process, prized in years past for its capacity to capture the mature, deep aroma of delicate flowers, such as jasmine or tuberose, that lost their precious aromatic bouquet in high-heat distillation. Enfleurage in the original French means to “impregnate with the scent of flowers.†It is also defined as “extracting perfumes by exposing inodorous oils or fats to the exhalations of flowers.â€
The technique uses animal fat (deodorized lard or tallow) as a waxy 'dress' for the flowers, allowing them to macerate for days on large glass plates in wooden frames. Fresh produce was added to the point of fragrance saturation. The fragrant fat 'pomade' was then washed with ethanol to render an 'absolute de chassis.' Two variations of the technique existed: 'cold' enfleurage, perfected in the 19th century and using no external heat, and 'hot' enfleurage, in which the fat was gently heated while the botanical matter was stirred into the fat.
This technique is not commonly used any longer in the perfume industry, due both to its prohibitive labor intensity and cost and to the existence of newer, more efficient extraction methods such as solvent extract and supercritical fluid extraction.