Essential Oil Extraction through Distillation

Essential oils are a hot topic these days, and we get a lot of inquiries as to the extraction of essential oils through distillation.

What are the most common forms of Essential Oil Extraction?

Essential oils can be extracted via two key methods: Distillation (includes hydro-distillation) and Expression. Several other methods also exist, but Distillation and Expression remains the two predominant ones.

The History of Essential Oil Distillation

Distillation appears to have been practiced throughout ancient times. Based upon the current interpretation Paolo Rovesti’s discovery of an earthenware distillation apparatus, the production or extraction of aromatic oils by means of steam distillation, has been known for 5000 years. During the fifth century AD, the famed writer, Zosimus of Panopolis, refers to the distilling of a divine water and panacea (a miracle cure that cures all diseases). Throughout the early Middle Ages and beyond, a crude form of distillation was known and 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.

Although an extensive trade of odoriferous material has been shown to have occurred in the ancient Orient and ancient Greece and Rome, the oils used were not essential oils per se, “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”.

In 900 AD, Avicenna, the famous child prodigy from Persia who wrote many documents on plants and their uses and also instructions for massage, was accredited with refining the process of distillation by improving the cooling system.

Today distillation is still the most common process of extracting essential oils from plants. The advantage of distillation is that the volatile components can be distilled at temperatures lower than the boiling points of their individual constituents and are easily separated from the condensed water.

How do I Distill Essential Oils?

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 remove 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 is 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.

What are the different types of Essential Oil Distillation?

The three types of distillation include:

Water Distillation

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 herb and leaf material. 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).

Steam Distillation

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.

Note on Boiling Point: The boiling point represents 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 normal temperatures. In the presence of steam or boiling water, however, these substances are volatilized at a temperature close to 100°C at atmospheric pressure.

What is Expression?

Expression, also referred to as cold pressing, is a method of extraction specific to citrus essential oils, such as tangerine, lemon, bergamot, sweet orange, and lime. In older times, expression was done in the form of sponge pressing, which was literally accomplished by hand. The zest or rind of the citrus would first be soaked in warm water to make the rind more receptive to the pressing process. A sponge would then be used to press the rind, thus breaking the essential oil cavities, and absorb the essential oil. Once the sponge was filled with the extraction, it would then be pressed over a collecting container, and there it would stand to allow for the separation of the essential oil and water/juice. The essential oil would finally be siphoned off.

What is Ecuelle a Piquer?  

A more modern method of extraction, and less labor-intensive, has been termed the ecuelle a piquer process that involves a prodding, pricking, sticking action to release the essential oil. During this process, the rind of the fruit is placed in a container having spikes that will puncture the peel while the device is rotated. The puncturing of the rind will release the essential oil that is then collected in a small area below the container. The end process is the same as above. The majority of modern expression techniques are accomplished by using machines using centrifugal force. The spinning in a centrifuge separates the majority of essential oil from the fruit juice.