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Essential Oils - Extraction
The term 'essential oil' is a rather loosely used expression, nowadays, and is used to refer to all aromatic products derived from natural sources, strictly speaking this is not necessarily accurate, as some fragrance products are only partially produced from essential oils, they are made up from 'concretes, absolutes, resinoids etc. and therefore can contain waxes, resins and other non-volatile components.
Absolutes by further solvent extraction from concretes
Absolute from Châssis absolute fom pommade
Butaflors extractions using butane
CO2 Extraction extractions using carbon dioxide
Concretes are solvent extracted using hydrocarbon type solvents.
Cutting method of 'stretching' essential oils
Essential Oils are produced by expression or distillation from natural plant materials.
Phytonic Extraction produced by non_CFC gaseous solvents.
Pomades produced by enfleurage at ambient temperatures using waxes.
Rectification and Adulteration changes made to the essential oils
Resinoids solvent extraction from natural resinous materials, using hydrocarbon solvents.
Tinctures are made through the maceration of the plant materials using an alcohol.
Essential Oils
Expression - There are four main methods of expressed extraction, which is the most commonly used extraction method for citrus oils from the peel of Lemon, Orange, Bergamot, Grapefruit, Mandarin, Lime and other citrus fruits.
1. Sponge Extraction the fruit pulp is removed from the fruit, the remaing rind and pith are then soaked in luke warm water for a short time, this makes the rind softer and more pliable, after the pith has absorbed water and become soft, the operator takes a sponge in one hand, and with the other presses the softened peel against the sponge, so that the oil-glands burst open and the sponge absorbs the exuded oil, which is then sqeezed into a collecting dish, and filtered, any water will settle to the bottom leaving the essential oill floating on top, from where it is poured off into containers. The whole of the above process is carried out in cool darkened rooms in order to minimize the harmful effects of heat and light on the oil.
2. Écuelle à piquer in this process an apparatus made of pewter, and takes the form of a cup-shaped funnel about 25 cm. across. It is provided with a lip and "' short, closed stem, which serves both as a handle and as a reservoir for the exuded oil. Projecting from the inner surface of the cup are numerous brass pins across which the softened peel is drawn with a rotary movement. The liquid exuding from the ruptured oil glands collects in the stem, whence it is transferred to a collecting vessel and treated as above.
Both of the above methods, although producing a very top quality oil, are labour intensive and are generally cost inhibitive, therefore the vast majority of citrus essential oils are now produced by the machine abrasion method.
3. Machine abrasion is where the outer peel of the fruit is scarified and then removed by machine and dropped into a flow of water, which carries the result to a large centrifugal separator machine, this spins the essential oil out of the rind.
4. Cold Pressed This form of expression extraction is also used to extract essential oils from nuts and seeds and from the rinds of citrus. Mechanical pressure is used to force the oils out. The oils extracted contain water, but this water will, in time, evaporate, leaving just the essential oils. The downside of using this extraction method is that the cold pressed oils spoil more quickly than those extracted using other methods.
Distillation - There are three main methods of distillation, steam, water, or dry distillation. Of which steam distillation is by far the most commonly used.
1. Steam Distillation this is simple distillation of plants and liquids at atmospheric pressures. The plant material to be distilled is placed into a distillation vessel where hot steam forced over the lant material, helps to release the aromatic molecules from the plant material since the steam forces open the pockets in which the oils are kept in the plant material. The molecules of these volatile oils then escape from the plant material and evaporate into the steam. This vapour or steam from the plant material than passes into a cooling condenser where it condenses back to a liquid. The essential oil is then decanted for use or further processing, the remaining water, once it is separated from the essential oil, nearly always carries the fragrance of the oil, giving us evidence, to some extent, that some essential oil molecules are water soluble.
1a. Hydro diffusion is where the steam is introduced into the distillation vessel at a high level, and the condensation of the oil containing steam mixture occurs below the area in which the botanical material is held in place by a grill. The main advantage of this method is that less steam is used, with shorter processing time and a higher oil yield.
2. Water Distillation in many ways very similar to steam distillation, except that the plant material is completely covered by water, and the water is then slowly heated, and brought to the boil. This method will protect the oils so extracted to a certain degree since the surrounding water acts as a barrier to prevent overheating. As an aid to heating the water in some distilations steam is introduced above the water level, sometimes called water and steam distillation.
2a. Cohobation When rose oil, for example, is extracted during water distillation, one main constituent - phenyl ethyl alcohol - dissolves into the water of the distillation and does not form part of the essential oil that is so extracted. The extracted oil is therefore not whole and in order to produce a "complete" oil, the phenyl ethyl alcohol needs to be distilled from the water in which it dissolved and added back to the "incomplete oil". When this phenyl ethyl alcohol is so distilled, it is added back to the original distillate, in the correct proportion, to form a complete and whole rose oil, and is then called Rose Otto.
3. Dry Distillation manufacturers will use dry distillation to extract high boiling point oils from wood. In this process heat, usually direct flame, is applied to a vessel containing the plant material. The high temperatures release the oils by evaporation. The vapour is piped away and condensed to give a mixture of liquid oils. Some of the components in the plant material degrade (pyrolyse) at the high temperatures used and add burnt, smoky notes to the odour of the oil. Cade and birch tar oils are the two major oils produced by this method.
Absolutes
Absolutes are produced by further solvent extraction from the concrete, using pure alcohol (ethanol) in which the waxes are only slightly soluble, this process is often repeated many times, producing an absolute with less and less wax. Even so, some absolutes will still contain small percentage (less than 2%) of wax, notably orange flower. The alcohol is gentle removed by evaporation aided with a partial vacuum in the final stages.
Some absolutes will still retain a smalll amount of alcohol, these are not recommended for aromatherapy work, because of these remaining impurities. In some absolutes a further stage of processing using molecular distillation will remove every last trace of the impurities.
Absolutes are usually highly concentrated viscous liquids, and in some cases solids or semi solids. A more recent developement in the production of absolutes involves extraction of the absolute from the aromatic material by use of liquid carbon dioxide, these oils are excellent odour quality and free from all impurities.
Absolute from Châssis when the flowers are removed from the pommade in the daily batches from the greased trays ("châssis"), some fat will adhere to these exhaust flowers. The fat contains botanical oil. Extraction of the flowers with a hydrocarbon type solvent will isolate the perfumed fat as a 'concrete de châssis' from which an Absolute from Châssis is in turn produced by alcohol extraction, chilling, filtration and evaporation.
Butaflor is a registered name (P Robertet & Cie) given to a series of highly concentrated perfume materials produced by extraction with butane at subnormal temperatures. The solvent is recovered be evaporation at room temperature (boiling point of butane is -0°.50C). The low extraction temperature and the selected solvent result in a pale-coloured, almost wax free and terpenless product. The method is particularily useful and advantageous when applied to very delicate or heat sensitive botanical materials, e.g. lilac flowers. jasmin, rose, lily of the valley (muguet), orange flowers etc. Certain staple materials are also treated in this method, e.g. ginger rhizomes. It should be kept in mind that not all Butaflors are completely alcohol solvent.
CO2 Extraction
A recent method is that of the carbon dioxide extraction. It employs a much lower temperature than that of steam distillation. This process was to introduce oils that remain close to the way they reside in nature. This is primarily due to the inert nature of the solvent and lower pressures. There is some disagreement to this theory in that due to the acidic nature of CO2 one could argue it is disruptive to the chemistry of the resultant oil. Whereas terpenes are often manufactured through the methodology of distillation, a lower terpene content is produced through a CO2 extraction, a higher ester range is manufactured, and the addition of molecules far to large to pass their way over through distillation can be found. These findings confirm that the oil does have more of the botanics inherent personality. The aromas of oils produced by this method are astoundingly true to those of the plant, and the extracts are very pure since the oils come into contact with only the carbon dioxide. Unfortunately, the complexity and costs involved in CO2 extraction makes these oils relatively expensive. For this reason CO2 extraction is usually limited to producing only expensive herbal or floral oils.
Concretes
Concretes are prepared from the raw materials, such as bark, flowers, leaves, herb or roots. The aromatic plant material is is subjected to extraction by hydrocarbon type solvents (alcohols or ethers). This method is used primarily when the essential oil is adversely affected by steam or hotwater distillation, it does also produce a more 'true to nature' fragrance. Some plants are both steam distilled and solvent extracted therefore giving the end user the choice. The solvent is evaporated off from the concrete leaving a pure plant extraction. The remaining residue is usually a solid or semi solid and of a waxy non-crystalline nature.
Phytonic Extraction
This extraction employs a family of benign non-CFC gaseous solvents, R134a, or refrigerant Hydroflurocarbon 134a, now called ‘florasol’. Beginning to replace CFC’s, chlorinated flurocarbons, in the early 1980’s it won the curiosity of the British microbiologist, Dr. Peter Wilde. Dr. Wilde brought this process into the spotlight of the essential oil manufacturing community, inventing the innovative extraction method of Phytonic Extraction. Being now in development over the past 10 years, the extracts were once called ‘phytols’, then ‘phytosols’ and now referred to as ‘florasols’. Oils extracted by this method are perhaps the close to their natural form as possible. While the process does not use ozone-depleting CFCs, it does use fluorocarbons (or correctly fluorohydrocarbons) which are also potentially harmful and do not seem adequate for heightened ecological consciousness.
Pomades
Pomades are produced by 'enfleurage', this is a method of non-volatile or fixed solvent extraction at ambient temperatures, probably one of the most ancient techniques used to extract essential oils from flowers that continued to produce perfume long after they were cut. Traditionally it was employed in the production of floral creams and lotions known as pomades. To make a pomade a sheet of glass is coated with a specially treated type of odour-free fat, called "chassis". Freshly cut flowers, such as jasmine, orange flowers, or tuberose are spread on the sheet and as they dry, after 24 or 48 hours ( 72 hours for the tuberose), their volatile oils become fixed in the chassis. The flowers are carefully removed and more flowers are added until the fatty base is completely saturated, at which point it is called "pomade".
Eventually the fragrance saturated fat would be wine alcohol treated to separate the volatile oil from the fatty base to produce an absolute. As soon as the alcohol evaporates from the mixture you are left with the essential oil. This is a very labor-intensive way of extraction, and a very costly way to obtain an essential oil and is nowadays only sometimes used to extract essential oil from tuberose and jasmine.
Most concretes contain about 50% wax, 50% essential oil, like jarmin, or in rare cases like ylang ylang up to 20% wax and 80% essential oil. The main advantages of a concrete is that they are more stable and concentrated than the essential oils.
Resinoids
Resinoids are produced from resinous material by hydrocarbon extraction, using solvents such as petroleum or hexane. In contrast to concretes, resinoids are extracted from dead organic materials whereas concretes are produced from organic material that was, at one time, living. Typical resins are balsams (Peru, Tolu or benzoin), resins (mastic and amber), oleoresins (copaiba balsam and turpentine) and oleo gum resins (frankincense and myrrh). Resinoids can be viscous liquids, semi-solids or solids.
Tinctures
The medicinal properties of herbs can be extracted using an alcohol, or a mixture of alcohol and water. The alcohol will act as a preservative, making an excellent way to store the products. Immerse the finely chopped herb in an alcohol (vodka) and water (refer to ratio lists for correct water/alcohol ratios) almost all tables will be based on 100% proof alcohol. Store in for 2 weeks away from direct sunlight, shaking occasionally. Strain through a cheescloth and then through a coffee filter, label and store in dark glass bottle in a cool dark place.
Rectification
The term 'rectification' encompasses a large number of changes which can be made to an oil e.g. some components of the oil can be removed in order to make the oil more soluble in alcohol and longer lasting e.g. deterpenation involves removal of terpenes. Deterpenation is used frequently for citrus oils.
Rectification can also cover certain adulterations. Many pure essential oils e.g. Melissa, or real 'organic' oils are very rarely sold 'pure', as they are so expensive.
Vacuum distillation - is used for most rectification and this involves fractional distillation under reduced pressure at certain temperatures, (depending on what is to be removed).
Rectification primarily removes residual water and very light fractions from the 'heads', and heavy sesquiterpenes and waxes of high boiling point from the 'tails' of the oils. Citrus oils are often de-sesquiterpenized.
Rectification can make different essential oils very similar.
Differential solubility - is also used for separating the more valuable oxygenating components from terpenes, as used for citrus oils industrially.
This method involves cold temperatures and is based on the varying solubility of the fractions in a particular solvent e.g. aqueous alcohol.
Centrifuges and counter-current extractors are also used.
Chromatography - using columns filled with silica gel etc. to separate off terpenes or other components.
Cutting and Adulteration
This is a means of making the original essential oil go further using a number of alternative methods:-
Nature identicals - are composed of components obtained from plant sources, which could be from the same species or from a completely different plant.
Synthetics - are composed of entirely synthetic components ie. chemicals made in laboratories from various starting materials including plant components. Some are very cheap and nasty, whilst others are so similar to the original natural products that most people cannot distinquish between them. Most expensive perfumes contain between approx. 50 - 100 ingredients, of which a high percentage are sybthetics.
Substitutions - are often done using cheaper plant essential oils e.g. Petitgrain for Neroli or Ajown for Thyme/
Dilutions - can be done using many chemicals and plant components to make a larger profit for the supplier e.g. DPG (di-propyl glycol), turpenine fractions, fixed oils.
Folding - involves mixing batches of the same essential oil, which can be stored for 2 years and could then be processed further to terpeneless or sesquiterteneless stages if required.
Co-distillation - Putting two different plants or plant parts in the still and steaming them together to produce one oil. Or adding an essential oil to plant material and distilling them together, again producing one oil.
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