In the last issue we discussed various fatty plant oils and their uses. In this issue I want to focus on essential oils. Unfortunately it would go far beyond the scope of this newsletter to discuss each and every essential oil - there are just too many of them and there are numerous decent books on the subject, which cover many oils in great detail. Instead, I will try to focus on the more general question - what are essential oils, methods of extraction, their uses and potential concerns.
Anybody who has ever stopped to take in the scent of a flower has experienced the effect of an essential oil. Essential oils are aromatic compounds, which not only occur in flowers, but also in leaves and roots. Note that essential oils from different parts of the same plant may have completely different scents and properties. Although known as 'oils' these compounds are chemically completely unrelated to fatty oils (such as olive oil etc.). Chemically they belong to the huge family of terpenes, which are ubiquitous in the plant world. Terpenes are very complex chemicals and some form enormously long chained molecules. Essential oils tend to consist of rather shorter sequences known as monoterpenes and sesquiterpenes or ring-like structures called 'benzene rings'.
Science regards essential oils in terms of functionality - they are considered 'the chemical weapons' of the plant world, as their compounds may deter insects, or protect the plant against bacterial or fungal attacks. They also may act as 'plant pheromones' in an effort to attract and seduce their pollinators.
More poetically inclined souls regard them as the essence of the plant's soul, their ethereal nature, concentrated as scent, through which plants communicate with their surrounding world. In human anatomy the olfactory centre is part of the oldest section of the brain, which is located in close proximity to the area which stores emotional memories and instincts. This is why our reactions to scents are rather irrational - they communicate with our mind at a sub-lingual level and appeal directly to our instincts. This also explains why perfumes can be so effective in attracting the opposite sex, or why certain smells conjure up intense emotions or memories.
Medical professionals are more interested in the medicinal properties of essential oils - many oils show antibacterial, fungicidal, relaxant, stimulating, antidepressant etc effects, and can be very effective therapeutic agents indeed. In recent years a new form of therapy known as Aromatherapy, has evolved, which is solely concerned with the therapeutic actions of essential oils. Aromatherapy provides a ver holistic approach as it affects both, the mental/emotional as well as the physical plane and a skilled aromatherapist will take both into consideration when blending their oils. The therapy usually consists of massaging the patient with a particular oil blend, but they may also be instructed to use a particular oil in a diffuser or other applications. Some aromatherapists may even blend special cosmetic ranges, such as facial crèmes and body lotions with particular essential oils to maximize their therapeutic effect. (This practice has become a bone of contention with regulators since fragrance components may be regulated under different rules than therapeutic agents, even if they are the same oils and used in the same concentrations.
The art of aromatherapy is really not as new as some might make us believe. In fact, it dates back thousands of years and was already practiced in ancient Greece, Egypt and India. Archaeological finds of ancient stills as well as perfume vials found in Egyptian graves verify the fact, although their purposes may have differed somewhat to those of modern practitioners. In the ancient world fragrance was very important, and long before people figured out how to capture the ethereal scents of plants, they burnt fragrant plants to perfume themselves or to make fragrant offerings to the Gods. The Gods were believed to sustain themselves on scents sent to heaven. Neglecting to burn incense would have meant abandonment of the Gods, while burning incense was to honour the Gods and to invite their benevolence and protective powers into one's life.
Likewise, when essential oils were discovered, they were primarily used as perfume, to delight the Gods, who love to walk with those who scent their bodily temples. The ancient Egyptians were masters of the art of perfumery. Scent was part of every aspect of their lives. (Some claim that this was merely to cover up the stench of rotting food or faeces and that lack of hygiene generally promoted the use of strong scents, but this is a modern prejudice, which does not necessarily fit the ancient reality; although it would fit the picture of Medieval Europe.) Not only the living used expensive perfumes and cosmetics, but even the dead were embalmed with fragrant resins, gums and oils and were perfumed so they would be well received by the Gods. They were even given vials of perfume as burial gifts to sustain them in the afterlife.
Essential oils are very volatile, meaning that they evaporate at room temperature. Some have a very low flashpoint, which means that they must be extracted very carefully in order to avoid losing some of their complex aromas or causing an explosion.
Essential oils are soluble in oil and alcohol. Due to their volatile nature they can be released through heat, by distillation, and, in some cases, even by cold expression.
Although essential oils are ubiquitous and occur practically in all plants and plant parts, the proportional quantities tend to be miniscule. Thus, in order to obtain even small amounts of essential oils vast quantities of plant materials are required. The resulting oil is an extremely highly concentrated product the power of which should never be underestimated.
This is the simplest, but also the least efficient method of extraction. The idea is to macerate fragrant plant materials, usually flowers or petals, in a scentless fatty oil base. This can be done as a cold or hot process. Heat facilitates the release of the essential oils, but it can also easily destroy them. Traditionally a large glass surface is covered in solid vegetable fat that is mixed with plant material. After three days the spent plant parts are taken out and replaced with a fresh supply until the desired concentration is reached. The saturated fat is now called 'pomade'. It is further processed by using alcohol to wash out the essential oil. The alcohol is evaporated, leaving a pure essential oil behind. The solid fat is sometimes used for soap making as some fragrant parts remain fixed within it.
This is by far the most common process of essential oil extraction. There are several different methods, which basically involve heat and water. The more elaborate process is done by heating water and passing it as steam through a vessel that contains the plant materials. The steam causes the oil glands to burst, and carries the volatile substance with it. A cooling coil is attached to the other end of the vessel, which causes the steam to condense and drip down into a collection vessel. In this process the essential oil and the water separate and the oil, which swims on top, can be siphoned off.
The old alchemists used a simpler method along the same lines. They would place plant materials and water a vessel and gently heat it so that the water, facilitated by the heat will release the essential oils and carry them off in the developing steam, which as in the first example, is lead into a cooling tube where it condenses and separates into water and oil components. This is the oldest method of extraction and sophisticated versions of it are still widely used. The problem with this method is that the heat will likely be too hot, thus destroying some of the more fragile components of the essential oil, or worse, running dry and burning the herbs - resulting in a distilled burnt fragrance - and /or cracking the still. Flowers are almost invariably too delicate to be subjected to this process, which destroys many of their aromatic components. The gentlest techniques distil at very low temperatures, but repeat the process several times - a time consuming and thus expensive method. The watery part of the distillate, also known as hydrosol or hydrolat (flower water), retains some of the fragrance and is often used in cosmetics.
Some essential oils are extremely sensitive to heat and are thus very difficult to distil. In order to extract these oils a solvent is used. This is usually hexane. The hexane dissolves the essential oils as well as other extractable substances such as waxes and pigments. This solution is then filtered and subjected to low pressure distillation, which results in a highly fragrant waxy substance known as a 'concrete', The hexane has thus been 'cleaned' and can be used again.
In a further extraction process, this time using heat and ethanol, the concrete is broken down. The essential oil combines with the alcohol, leaving the wax behind. However, the resulting mixture still contains some waxy parts and other impurities and is further purified and separated. It is a lengthy process involving freezing and stirring the mixture, which helps the waxes to precipitate out. The resulting oil is called an 'absolute'. Most flower oils are absolutes. Many Aromatherapists tend to shun absolutes as some solvent particles and impurities remain. Perfumers are less fussy as they work with alcoholic extracts all the time.
This is a pretty new method of extraction and much 'cleaner' than solvent extraction. CO2 is gaseous at normal pressure, but at high pressure transforms into a liquid. In this liquid state it can be used to extract the volatile oils. When the CO2 is depressurized it reverts to a gas, leaving no solvent particles behind in the essential oil. This process has made it possible to extract oils from hitherto never before processed plants, such as calendula, coffee, or rosehip seed, to name but a few. CO2 extracts are more complex as more of the fragrant components of the plant material are extracted. Some of the waxes are also extracted, which often results in a rather pasty substance.
While potentially this is the cleanest method of extraction, - in some instances the plant material is first subjected to hexane extraction producing a concrete, which is then processed using the CO2 extraction method. This is often the case with floral CO2 extracts, such as Rose or Jasmine. The equipment for this novel technique is still very expensive, which is reflected in the price of the oils that are extracted this way.
Cold Pressed Oils
This process is only practical with very few oils, most notably the citrus oils, the rinds of which are so densely covered with oil glands that mere pressure is sufficient to extract them, as anybody who has ever peeled an orange can testify. In this process the rinds of citrus fruit, such as orange, bitter orange (bergamot), lemon, lime, mandarin, tangerine and grapefruit, are cut into small pieces and subjected to pressure. The resulting liquid is a somewhat watery essential oil. This hydrous component is the reason why cold expressed citrus oils don't have a long shelf life.
Uses of Essential Oils
Essential oils are used in a myriad of household products, most notably as flavouring in the food industry, and to aromatize cleaning materials, soaps, detergents and cosmetics - not to forget perfumery of course! Unfortunately many natural oils are replaced with synthetics - which are supposed to be aroma identical, but in fact, are not. There is a chemical reason for this, which is too complex to explain here. Suffice to say that man just has not yet been able to reproduce nature's tricks. Although a chemical can be produced with much greater consistency than a pure essential oil, they lack the complexities and depths of their natural counterparts, The specific qualities of an oil may vary depending on where their source plant was grown, when it was harvested and what kind of climatic conditions the particular batch has been exposed to - much like good wine, essential oils have a vintage. No two oils, even of the same plant, will ever smell the same.
Despite their widespread use there are a number of safety concerns regarding essential oils. Essential oils are very potent and some of their components may be carcinogenic, phototoxic, photosensitizing, or allergenic. Currently there is a great conundrum raging over safe levels of certain chemicals within blended products and even over particular oils themselves. This hysteria is due to the fact that scientists have a tendency to regard the action of component parts as equal to the sum total of all parts. In other words, it is assumed that if an oil contains a certain compound, say a ketone, and ketones generally speaking are lipolytic, mucolytic and sedative, that the oil itself will have these characteristics. But in real life the sum total of 'ingredients' creates a synergy all of its own, which may or may not actually produce any of these effects. As essential oils can be composed of lots of different compounds, some known and some unknown, it is impossible to judge their safety by analyzing the effects of its known parts alone. It would make more sense to take heed of specific well known and commonly observed effects. Another flaw lies in the assumption that the metabolism of rats and humans are sufficiently similar to draw parallel conclusions regarding the effects of essential oils. While some may indeed act the same way, other oils may be toxic to rats, but perfectly safe to humans, or vice versa.
For safety's sake certain precautions should always be taken:
Use oils only in dilution, and, if you are unfamiliar with a particular oil and its effects on you (everybody reacts differently), use the skin patch test: dilute the essential oil in base oil and apply to a small area of the inner arm. Wait at least 6 hours to observe any skin reactions. If you notice any adverse signs, do not use the oil.
Some people are even sensitive to diffused oils. If you notice any ill effects, e.g. difficulties in breathing, headaches, itching, etc. do not use the oil in an infuser either.
Remember that a little goes a long way. Even one drop of essential oil can contain the power of a kilo of its source plant.
People who use essential oils professionally, e.g. perfumers or aromatherapists, or people who make their own cosmetic products should be extra careful:
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