Distillation Extraction

The Process of distillation falls in to three stages:

1. Converting a volatile liquid  into a vapour

2. Condensing the vapour by cooling.

3. Collecting the condensed liquid.

It is the most popular and cost effective method used today for producing essentials oils.

Distillation can be divided into the following:

(A)   Water Distillation: - The botanic material is completely immersed in water and the still is brought to the boil. This method protects the oils so extracted to a certain degree since the surrounding water acts as a barrier to prevent it from overheating.

When the condensed material cools down, the water and essential oil is separated and the oil decanted to be used as essential oil. The water that is so separated in this process is also used and is marketed as "floral waters" (also called hydrosol or sweet water) - such as rosewater, lavender water and orange water. Water distillation can be done at reduced pressure (under vacuum) to reduce the temperature to less than 100 degrees, which is beneficial in protecting the botanical material, as well as the essential oils.

Neroli oil, which is sensitive to heat, can therefore be successfully extracted using this method.

If extended exposure to hot water is not indicated for a particular plant - such as lavender, it is best to find an extraction method better suited. Any botanical material that contains high amounts of esters do not take well to this extraction method, since the extended exposure to hot water will start to break down the esters to the resultant alcohols and carboxylic acids.

(B) Steam Distillation: - The botanical material is placed in a still and steam is forced over the material. The hot steam helps to release the aromatic molecules from the plant material since the steam forces open the pockets in which the oils are kept in the plant material. The molecules of these volatile oils then escape from the plant material and evaporate into the steam.

The temperature of the steam needs to be carefully controlled - just enough to force the plant material to let go of the essential oil, yet not too hot as to burn the plant material or the essential oil. The steam which then contains the essential oil, is passed through a cooling system to condense the steam, which forms a liquid from which the essential oil and water is then separated. The steam is produced at greater pressure than the atmosphere and therefore boils at above 100 degrees Celsius which facilitates the removal of the essential oil from the plant material at a faster rate and in so doing prevents damage to the oil.

Some oils, like Lavender is heat sensitive (thermolabile) and with this extraction method, the oil is not damaged and ingredients like linalyl acetate will not decompose to linalool and acetic acid. The extract is purified through centrifuging and filtering.

(C) Hydro Diffusion: - In hydro diffusion the steam is fed in from the top onto the botanical material instead of from the bottom as in normal steam distillation.

The condensation of the oil containing steam mixture occurs below the area in which the botanical material is held in place by a grill. The main advantage of this method is that less steam is used, shorter processing time and a higher oil yield.

(D) Cohobation: - When rose oil is extracted during water distillation, the one main constituent - phenyl ethyl alcohol - dissolves into the water of the distillation still and does not form part of the essential oil that is so extracted. The oil so extracted is therefore not whole, and is deficient in this rose-smelling ingredient - and in order to produce complete oil, the phenyl ethyl alcohol needs to be distilled from the water in which it dissolved and added back to the incomplete oil. When this phenyl ethyl alcohol is so distilled, it is added back to the original distillate, in the correct proportion, to form a complete extraction.

(E) Rectification: - When an essential oil contains any impurities, it can be purified by re-distillation - either in steam or in a vacuum and this purification by re-distillation is referred to as rectification. An example of this is eucalyptus oil that is marketed as "double-distilled". This is not the same as chemical or heat refining and is used to produce oil of standard quality.

(F) Fractional Distillation: - This process is carried out similarly to normal distillation but the essential oil is collected in batches as distillation proceeds. These batches are called fractions