Essential oils are not all the same. Each has its own fragrance, properties and peculiarities. Each behaves in its own characteristic way. Perhaps it boils at a particularly high temperature (useful as a fixative), or has a high antiseptic value or perhaps it contains a rare therapeutic agent such as azulene (in chamomile). Whatever the reason for its uniqueness no essential oil is the same as any other and this includes oils distilled from plants of the same species in different places or at different times. For these reasons, anyone who wants to understand essential oils must understand the individual characteristics of all the oils he/she uses. However, there are some generalisations that can be made about essential oils, as follows: -

Essential Oil - Definition Essential oil is distilled or pressed from plant parts. The product so obtained may or may not be further refined depending on circumstances. Regardless of its origin an essential oil is volatile which means that it will evaporate into the air. Essential oils dissolve in alcohol and in fixed oils but not in water.

The word essential is misused in English to imply importance or necessity when, in fact, it is the adjective formed from the noun essence. Other languages are more specific. Arabic, for instance, uses the word ruh that means spirit or breath, implying that the fragrant oil is the very life of the plant from which it was obtained.

The most common misunderstanding about essential oils is that they are produced by steeping the plant parts in a fixed oil. It is possible to produce a mildly fragrant oil in this way but nothing so powerful, intense and persistent as an essential oil or an absolute.

Absolute - Definition An oil produced by solvent extraction. Quality jasmine oil is only extracted by this method. Rose oil is produced both as an Otto (by distillation) and as an absolute. The two products differ considerably largely because phenyl ethyl alcohol (one of the constituents responsible for the fragrance) is soluble in water and, therefore, hardly present at all in the Otto.

There used to be concern that some of the solvent remained in the oil. These days though, extraction by carbon dioxide or hexane is extremely sophisticated and the possibility of solvent residue is not an issue.

Absolutes dissolve in alcohol and fixed oil but not in water.

Fixed Oil - Definition Vegetable oil (usually cold pressed), e.g. sweet almond which does not evaporate at all. Fixed oils have no fragrance value but find extensive use in aromatherapy and cosmetics.

Expression
The simplest extraction process, expression is most suitable for fruits whoe oil, contained within the peel, is liberated when the tiny capsules that contain it are burst. When the fruit has been separated the peel is put into presses and the oil is squeezed out. With the oil come water and impurities that must be removed before the oil can be used. Fruit oils can also be distilled. In the case of bergamot and lemon, for example, the distilled product contains no furo-coumarins and this makes for a safer oil for both therapist and patient.

Distillation
The most common extraction process. In its simplest form distillation entails immersing plant parts in water, boiling the mass and collecting the liquid which accumulates from the vapour produced. Although this method may be considered crude it remains the most effective way of extracting delicate oils such as rose and orange blossom since the highest temperature that can be reached is 100c.

Using steam distillation quite high temperatures can be reached, especially under pressure. Superheated steam is passed through the plant parts and then condensed whereupon the oil separates from the water. High temperatures liberate aromatic substances that might otherwise be difficult to extract.

Solvent Extraction The traditional way to capture the fragrance of delicate flowers (enfleurage) uses warm or cold lard as a solvent. Flowers are placed on chassis; wooden framed sheets of glass onto which lard has been spread. Over the ensuing hours (or days!) the lard absorbs the aromatic constituents of the flowers. The flowers are then removed and the chassis is recharged with fresh flowers, this process being repeated until the lard is saturated. The resulting waxy and fragrant substance, the pommade, is then subjected to alcohol to wash out the oil it contains. The alcohol can then be evaporated off leaving the absolute from pommade.

The enfleurage process is seldom used today but perfumers look back to the old fashioned product with a certain nostalgia since it allowed enzymatic decomposition to take place and this resulted in some exciting peculiarities of odour. As the name implies, solvent extraction causes substances such as petroleum ether to pass through the prepared plant parts. The solvent is then evaporated off leaving a mixture of waxes and oil. This is called the concrete. After the removal of the waxes there remains the highly fragrant, intensely strong substance known as the absolute.

Perfumery and aromatherapy are related disciplines and to understand one of them it is an advantage to know at least something of the other. The aromatherapist needs to know how to blend therapeutic oils for the maximum effect and yet achieve a product that is also pleasing in its fragrance. The perfumer needs to be aware of the physiological and psychological effects of the oils in order to induce in the person who wears the product a feeling of well-being and specialness.

Copyright 2001 Hermitage Oils