Distillation of Essential Oils, Part One
Methods of Extracting Essential Oils
There are many different ways to extract essential oils and absolutes (also called extracted oils). They include:
Carbon Dioxide Extraction
Warm Oil Infusion
How Are Essential Oils Extracted?
Essential oils can be extracted via two key methods: distillation (includes hydrodistillation) and expression.
How are Absolutes (Extracted Oils) Extracted?
Absolutes, on the other hand, can be extracted via solvent extraction or enfleurage, although enfleurage is rarely performed via the original process any longer. Enfleurage used to be performed using sheets of fat as a solvent and was difficult and expensive.
Now, the more common aromatic product derived from solvent extraction are CO2 extracts. They differ in chemistry from their related steam distilled essential oils, but are becoming increasing popular and available, due to decreased costs in creation. Some holistic practitioners refuse to use CO2 extracted oils, as they believe some of the CO2 remains behind.
The Practice of Distillation
There is evidence that distillation was practiced throughout ancient times. Based upon the current interpretation of Paolo Rovesti’s discovery of an earthenware distillation apparatus, the production or extraction of oils by means of steam distillation has been performed for approximately 5000 years.
During the fifth century AD, the famed writer Zosimus of Panopolis referred to the distilling of a divine water and panacea. Throughout the early Middle Ages, a crude form of distillation was used primarily to prepare floral waters or distilled aromatic waters. These appear to have been used in perfumery, as digestive tonics, in cooking, and for trading. References to holy oils extracted from plants appear in ancient Egyptian, Babylonian, and Aramaic texts.
Although an extensive trade of perfume and sacred oils has been shown to have occurred in ancient Asia and Greece and Rome, the oils used were not essential oils, “rather they were obtained by placing flowers, roots, and other plant material into a fatty oil of best quality, submitting the glass bottles containing these mixtures to the warming influence of the sun and finally separating odoriferous oil from the solid constituents”. This would be a warm oil infusion, rather than steam extraction.
In 900 AD, Avicenna, the famous child prodigy from Persia who wrote many documents on botanicals and their uses and instructions for using oils in massage, was credited with refining the process of distillation by improving the cooling system.
Today distillation is still the most common process of extracting essential oils from botanical material. The advantage of distillation is that the volatile components can be distilled at temperatures lower than the boiling points of their individual constituents - these are then easily separated from the condensed water.
The Distillation Process
During distillation the plant material is placed upon a grid inside the still. Once inside, the still is sealed, and, depending upon the above methods, steam or water/steam slowly breaks through the plant material to separate out its volatile constituents.
These volatile constituents rise upward through a connecting pipe that leads them into a condenser. The condenser cools the rising vapor back into liquid form. The liquid is then collected in a vehicle below the condenser.
Since water and essential oil do not mix, the essential oil will be found on the surface of the water where it can be siphoned off. Occasionally an essential oil is heavier than water and is found on the bottom rather than the top, such as with clove essential oil.
There are actually three different steam processes that are described further down. In all of the methods, steam is used to rupture the oil membranes in the plant and release the essential oil.
The essential oil distilling equipment including the condenser, separator and cooking chambers can all have an enormous impact on the quality of the oil. As well as, the distillation temperature and pressure. There is a difference in essential oils produced in a lab grade glass still and a copper still.
And even if everything appears correct, the process can still produce oils that don’t meet the standards set by different herbal organizations and standardization organizations (such as AFNOR). So essential oil distillers must have the knowledge and expertise to know how to produce therapeutic and medical grade essential oils.
The three types of distillation include:
The plant material comes into direct contact with the water. This method is most often employed with flowers (rose and orange blossoms), as direct steam causes these flowers to clump together, making it difficult for steam to pass through.
Water and Steam
This method can be employed with herbaceous, leafy materials. During this process, the water remains below the plant material, which has been placed on a grate while the steam is introduced from outside the main still (indirect steam).
This method is the most commonly used. During this process, steam is injected into the still, usually at slightly higher pressures and temperatures than the above two methods.
Why Steam Distillation is So Effective – Boiling Points
The boiling point designates the temperature at which a liquid is converted to a gas at a specified pressure. The fundamental nature of steam distillation is that it enables a compound or mixture of compounds to be distilled (and subsequently recovered) at a temperature substantially below that of the boiling point(s) of the individual constituent(s).
Essential oils contain substances with boiling points up to 200°C or higher, including some that are solids at room temperature. In the presence of steam or boiling water, however, these substances are volatilized at a temperature close to 100°C.
Percolation or Hydro-diffusion
This is a relatively recent method. It is very similar to steam distillation, except that the steam comes in through the top rather than the bottom, and there is a shorter distillation time. It is useful in extracting essential oils from woody or tough material, or from seeds such as fennel and dill.
Percolation is one of the newer methods of extraction essential oils. It has been used successfully in France; however sometimes an emulsion is produced that can not be separated out, so until it can be further developed you will not see it on a large scale.
Percolation is often used to create cocoa nut oil and kaffe nut oil.
Fractional distillation separates the volatile oil in different fractions or portions at various boiling points. This is used in oil refineries for distillation of petroleum products and is not suited for therapeutic or medical grade essential oils.