Essential oils or plant essences are the concentrated extracts of certain plants described as aromatic. Essential oils have been known and appreciated since the earliest times for their healing properties and are the main active ingredients in nature's medicine chest. They are also used in the perfume industry and to flavour a wide range of foods and drinks.
These essences are obtained either by steam distillation in a still for aromatic plants, or by pressing for citrus fruit essences. These procedures give the most natural extracts that are fit for human consumption.
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Pressing:
This method is only used for citrus skins.
If you squeeze an orange-skin over a candle-flame you may notice that tiny sparks crackle in the flame. These are the "little stars" contained in the orange zest that are pressed out and bottled.
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Distillation:
This is the commonest process. Plants are placed in the still vessel in a basket to make them easier to remove. The vessel is then hermetically sealed. Steam is then passed over the plants as in steam cookery. The steam carries the aromas of the plants through the swan neck into a coil submerged in a tank of cold water. The steam cools as it passes through the coil and the vapour condenses.
The vapour, which is now once more liquid, divides into two components with different densities: the essential oil and the floral water. Most of our essences are lighter than water and we therefore collect them in the upper section of the separator, which is known as the essence chamber or Florentine vase.
There are a large number of types of still, many of which are the product of researchers' imagination.
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Effleurage:
Effleurage is a very ancient process based on the observation that fats are capable of absorbing doors.
Effleurage has been practiced using a range of oils since ancient times. Ben oil and almond oil have both been used. Recent experiments in Grasse, the capital of the French perfume industry, have successfully used more solid fats such as lard (pig fat). This technique has become a specialty in Grasse for use on plants such as jasmine, tuberose and locally grown daffodils. The use of this process is now becoming increasingly rare.
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Solvent extraction:
This industrial procedure is commonly used in the manufacture of aromas for the perfume industry. The procedure is used to extract certain molecules that steam is incapable of removing. For example, the essential oil of clary sage that can be obtained by distilling with steam only contains 0.9 % to 1.6 % of the essential oil sclareol, whereas the so-called "concrete" extracted using hexane contains 60 to 65 % sclareol.
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Destructive distillation:
The extraction of tars and resins in a closed vessel is used almost exclusively to obtain cade oil, also known as Spanish juniper oil. This is an oil obtained from a variety of juniper and used in the cosmetics industry and hair-restorers.
Other techniques for extracting aromas are known but not yet used on an industrial scale. These include the use of hypercritical carbon dioxide gas or micro-waves.
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