Essential oils are the volatile substances that a plant owes its odour and flavour to and are often referred to as the soul or the hormones of the plant. Essential oils are found in different parts of plants (leaves, flowers, bark, fruit etc.). For example Lavender essential oil is obtained from the flowering tops of the plant, rose oil from the petals, patchouli oil from the leaves, sandalwood from the wood and lemon oil from the rind. The amount of oil which can be extracted from the plant varies tremendously, for example to produce one drop of pure rose oil it takes 30 rose petals, whereas clove oil yields a much higher amount of oil and therefore less is needed. Pure essential oils can be very expensive as they are the pure oil from the plants and have been unadulterated unlike other less therapeutic oils such as fragrant oils or synthetic oils.
WHY ARE ESSENTIAL OILS THERAPEUTIC AND COMMON PERFUMES NOT?
The perfume industry is the biggest user of essential oils and historically traditional French perfumes always contained a high amount of aromatic essential oils. These days synthetic versions of the oils can be produced and many of the perfume manufacturers choose these substances to produce perfumes as they are cheaper. However this means that the aroma does not emit powerful therapeutic qualities nor any synergism is gained from the blending of these inferior smells.
Synergism describes how substances work in combination and is defined as the joint action of agents so that their combined effect is greater than the algebraic sum of their individual parts Encyclopaedia of Medicine, Nursing and Health 1978.
Simply speaking this means that the therapeutic action of any natural substance is due to the combined effect of all its constituents, this natural combination is in fact more powerful than just a simple combining of chemicals in the laboratory.
During distillation, only very small molecules can evaporate, so they are the ones that leave the plant. These extremely small molecules make up an essential oil. Oils containing more of the smallest and therefore most volatile of these tiny molecules are termed top notes. Those containing more of the heaviest and least volatile of the tiny molecules are called base notes. Those in-between are known as middle or sometimes heart notes.
Top notes are generally the smells that you immediately notice when smelling a blend, for example the light flowery aromas, they are quick to wear off but are delightful to the senses. Base notes are the ones that are left after wearing an aroma blend for some time, they linger and are more grounding in effect. Some essential oils can be found in more than one note.
- Top notes – basil, bergamot, cajuput, cinnamon, clary sage, corriander, eucalyptus, grapefruit, hyssop, lemon, lemongrass, lime, mandarin, neroli, verbena, orange, niaouli, peppermint, pettigrain, sage, spearmint, tangerine, tea tree, thyme
- Middle notes – bay, black pepper, cardamom, chammomile, cypress, fennel, geranium, hyssop, juniper, lavender, marjoram, melissa, myrtle, nutmeg, palma rose, pine, rosemary, yarrow
- Base notes – cassia, cedarwood, cinnamon, clove, frankincense, ginger, jasmine, myrrh, neroli, patchouli, rose, rosewood, sandalwood, valerian, vanilla, vetiver, ylang ylang
PREPARATION OF ESSENTIAL OILS
Essential oils are extracted in a number of ways, depending on the type of the plant used. The following are various methods used:
- Steam distillation is the oldest method of separating essential oils from the plant. The plant material is steam heated in a still and the vapour is passed through a condenser where it is cooled. The resulting liquid consists of oil and water, in most cases the oil floats to the top. Examples of essential oils extracted by steam distillation are lavender, rose geranium, rosemary, eucalyptus, peppermint, cinnamon and cajuput.
- Enfleurage is a process which utilises fat to absorb the essential oils from the plants. The fat used is pure and odourless and unlikely to turn rancid. There are many different recipes and enfleurage involves the use of cold fat to produce the pomade. This process can only be used for flowers that continue to generate essential oils are being harvested. Some examples of this are jasmine and rose.
- Maceration extracts essential oils using fat but is used with those flowers that do not generate essential oils after harvesting. In this process the flowers are plunged into hot fat which penetrates the cell walls of the plant and absorbs the essential oil content. The flowers are strained and more are added in a process that continues for up to 15 cycles and the essential oils are then extracted from the resulting pomade.
- Absolute is prepared from a pomade by adding an alcohol to extract the aromatic (alcohol soluble) molecules. The alcohol is then evaporated off gently under vacuum, leaving the absolute which is a thick, coloured liquid with an extremely powerful aroma.
- Solvent Extraction is applied to gums and resins. The base materials are placed in a container and covered with a solvent which is slowly heated. The solvent is then evaporated to yield a resinous oil. Some examples of this method are myrrh, frankincense and cedar wood.
- Expression is the process used to produce citrus oils such as orange, lemon, mandarin, grapefruit and tangerine. Historically extraction was done by hand by squeezing the rinds of the fruit into a sponge and when saturated the sponge was squeezed out. This was a rather costly way to produce oils and the same process is now done by machines.
- Sunlight infusion is a home friendly method of obtaining essential oils from flower petals, although this way produces a good quality oil it cannot be labelled an essential oil. The process to release the aromatic properties is to place 50g of crushed flower petals into a screw top glass bottle and add 300ml of odourless oil, leave the jar in the sun shaking every day for 2 weeks and then strain. Add another 50g of flower petals (but no more oil) and continue the shaking process daily for another 2 weeks and then strain. The oil should now have a strong aroma and can be used.
- Cold Pressing relates mainly to the vegetable oils used as carrier oils in aromatherapy blends. This process is used to obtain high quality oils of soya, olive, coconut, avocado, sweet almond, macadamia etc. Commercially most vegetable oils are extracted using heat and this can destroy a lot of the important constituents leaving them denatured. The finest oils are cold pressed and this process crushes the ingredient between cold rollers thus releasing the oil and retaining the natural properties. Oil yield by cold pressing is lower than with heat extraction and cold pressed oils should be refrigerated and they do not contain added antioxidants to keep them from turning rancid.
WHAT MAKES ESSENTIAL OILS
Each essential oil is composed of a number of naturally occurring molecules and owes its unique aroma and therapeutic properties to the individual combination of molecules.
- Acids – organic acids are not like inorganic acids which are potentially dangerous. Acids in their free state are rare in essential oils and occur in minute quantities. They are water soluble, colourless and have a characteristic sharp taste. Their therapeutic action is as an anti-inflammatory
- Alcohols – Monoterpenols are a component of alcohols and are strong bactericides, anti-infectious, antiviral, stimulating, warming and general tonics. Sequiterpenols are another component of alcohols and are decongestant to the circulatory system and are non-irritating. Alcohols are easily identified on labels as they are the ingredients ending with ol. Examples of alcohols are Menthol (peppermint oil), Geraniol (geranium oil) and Lincol (lavender oil).
- Aldehydes are very important to the perfumer because they often have a very powerful aroma. The are easily identified on labels as they are the ingredients ending with al. Aldehydes are similar to alcohols and ketones and tend to be skin irritants. Examples are Citral (lemongrass), Citronellal (eucalyptus, cinnamon) and Vanillin (cloves).
- Esters are gentle in action and are anti-inflammatory, calming, uplifting and tonifying and balancing to the nervous system. Esters are easily identified on labels as the ingredients ending with ate.
- Coumarins are generally found to be sedative in action and are also noted for their anti-coagulant properties. An example is Bergapten (bergamot oil).
- Ketones are not terribly user friendly as several appear to be neurotic (but not all of them are). Their effects are calming, sedating, they break down mucus and encourage the healing of wounds. They should be used with caution, infrequently and not for a prolonged time. Ketones are easily identified on labels as they are the ingredients ending with one. Examples of Ketones in essential oils are Carvone (spearmint, Caraway), Thujone (Hyssop), Pulegone (pennyroyal, Sage).
- Oxides are rare in essential oils, its major effect is due to its mucolytic properly in coughs, colds and congestion of the respiratory tract. It can be skin irritating so caution is recommended. Some examples are Hyssop, Eucalyptus, Marjoram and Cajuput.
- Phenols are very active and stronger than alcohols (Phenols also end in ol). They are powerful anti-septics, bactericides and are stimulant to the nervous and immune systems. These should be used in low concentrations and for short periods of time as they can be skin irritants. Some examples are Thymol, Carvacrol (thyme), Safrol (yang yang) and Eugenol (cinnamon, cloves).
- Terpenes occur in all essential oils and their effects are anti-septic, bactericidal, stimulating, expectorant and slightly analgesic and some are anti-viral. Some may be slightly irritating to the skin and should be used in a carrier oil, for example all citrus oils contain a high percentage of terpenes. Some examples are Camphene (juniper, rosemary), Pinene (thuja, ylang yang) and Limonene (bergamot, hyssop, lemon)