THE DIFFERENT METHODS OF EXTRACTION OF AROMATIC MOLECULES
This method is the easiest but unfortunately also the most limited one. It consists of mechanically breaking the "essence bags" contained in the fresh peel of Citrus fruits in order to collect their essences. This very traditional method is only possible with fruits from the Rutacea botanical family (all the Citrus fruits such as lemon, orange, bergamot ...). The final product obtained is called "essence" instead of "essential oil" because the aromatic active molecules have not been submitted to the physico-chemical action of a solvent or a steam distillation but to a simple mechanical expression.
The steam distillation
A direct distillation (without steam water) is not feasible because it could only happen at high temperature at which the common aromatic molecules would undergo some important biochemical modifications and pyrogenic changes, leading to the synthesis of highly toxic substances.
The steam water distillation is a method of concentration of aromatic compounds dating back to time immemorial. The method has been transmitted by the Arabs and has been further developed and improved by the people of Grasse (the perfumes capital, France). The general mechanism of steam water distillation consists of sending steam at controlled low pressure through a tank filled with a given aromatic plant material. Essential oils are volatile, which accounts for their perfumed nature and enables them to be carried out with the steam. Afterwards the steam enriched with aromatic material passes through a coil bathing in fresh water; at this moment both steam and aromatic molecules condense. Because of their lower density compared to water (lower density) they are not miscible (soluble) into liquid water, which makes their physical separation into the collecting tank (called "essencier") possible.
The wild mountain plants have extraordinary smell and biological activity due, for some of them, to the high level of aromatic esters, the synthesis of which being promoted by the altitude, the sunniness and/or the dryness, or being a result of a particular symbiosis with other wild plants of the biotope.
When the plant material has been harvested, collected and botanically identified, the process of steam distillation requires several very important precautions:
- The choice of the Alembic is of great importance (ideally made of stainless steel, the most inert material)
- The heating of water must be conducted very carefully, under very low pressure
- The duration of the whole distillation is of great importance : long and prolonged, it will allow to collect a complete essential oil containing its base and top fractions (or notes)
- The use of spring water, poorly calcareous, is always preferable
The obtained essential oil (E.O.) must be:
- 100% NATURAL: it means that the essential oil must not be adulterated with synthetic of semi-synthetic compounds, which are more allergenic, toxic and less effective than natural aromatic molecules
- 100% PURE: the essential oil must be free of closely related and/or similar essential oils. This can be achieved after a scientific botanical determination of the raw material before the beginning of the steam distillation.
- 100% INTEGRAL: the process of steam distillation must be conducted until the last drop of essential oil, in order to contain the base and top fractions.
To cut, to dilute, to adulterate, to chemically modify a natural essential oil is – in theory – strictly forbidden. People doing so are known "to water down the sauce".
The "Enfleurage" method is restricted to flowers containing very tiny concentrations of essences (jasmine, rosa centifolia, mimosa ...). The flowers are put in contact with absorbing fats which become gradually saturated in essences. Afterwards rough aromatic extracts are isolated by centrifugation; they are use as such (the extracts is called "concrete") or are further purified by using absolute alcohol. The obtained alcoholic extract is called "absolute".
The red oil (St John's wort), the green oil (oregano) are not essential oils but are vegetable fatty oils in which a certain amount of therapeutically interesting plant extracts are put to form a "macerate". After a couple of week the aromatic molecules have migrated into the vegetable oil and the refined extract is called "maceration oil".
Warning : Do not confuse "essential oil" and "maceration oil"
Tip : the aromatic vinegars are made by using the same procedure as the maceration oils.
The process of "Depletion"
Here the aromatic essences are extracted by chemical volatile solvents (benzene, hexane, toluene ...). The obtained solutions are called "concretes of flowers and leaves" and become "absolutes" after purification (literally "depletion" or "exhaustion") with absolute alcohol. This type of essences generally contains 2 to 6 % residual solvents and may not be used for therapeutic purposes because of this chemical "pollution" of toxic solvents.
DISTILLATION OF ESSENTIAL OILS
The yields of distillation of aromatic plants may vary a lot from one species to another. It goes without saying that the more plant material you need to produce the essential oil the more expensive will be the final product.
To obtain 1 kg of its essential oil, it requires:
- 7 kg of dried buds of clove (Eugenia caryophyllus)
- 50 kg of lavandin (Lavandula reydovan)
- 150 of true lavender (Lavandula angustifolia)
- 1 ton of everlasting (Helichrysum italicum)
- 4 tons of petals of Damascus rose (Rosa damascena)
- 5 to 10 tons of melissa (Melissa officinalis)
The yields of distillation also depend on several other criteria:
- It can simply vary from one year to another for the same plant, depending on several climatic conditions... One can speak about "vineyards" or "vintage wine" also for essential oils "vintage essential oil".
- A splendid spring season will promote the biosynthesis of terpenic alcohols (linalol, geraniol ...) whereas a sunny and mild autumn will favour the production of aromatic phenols (thymol, carvacrol ...)
- Some aromatic plants must be harvested and distilled during specific periods of the day (early in the morning, late in the evening ...)
- The mineral and biochemical nature of the ground, the presence of competitive vegetal species, the local weather conditions, the amount of days of sun, the global sunniness... are other factors influencing the yield of distillation and the biochemical composition of a given essential oil.