The Extraction of Essential Oils by Hydro-Diffusion (Percolation) and Carbon Dioxide Extraction

Photo of a Simple Homemade Still

As discussed in the post The Extraction of Essential Oils by Distillation and Expression, there are now new methods of extracting some essential oils. Both hydro-diffusion and carbon dioxide extraction are new methods, and there are some essential essential oils for sale which will be described as, for example, 'CO 2 extracted'. Although distillation of essential oils remains the most popular and most frequently used method of extracting essential oils, it is worth mentioning the two newer methods of hydro-diffusion and carbon dioxide.



- Hydro-Diffusion Extraction (also known as percolation) - is the newer of these two extraction methods for essential oils. It is quicker than distilling an essential oil and works much like the process of a coffee percolator (hence its alternative name of percolation). As it is a fairly new procedure for extracting essential oils, it is not known yet whether essential oils obtained through hydro-diffusion extraction is of the same quality as those obtained through distillation. Additionally, not all essential oils, are suitable for hydro-diffusion.



- Carbon Dioxide Extraction - as the name suggests, carbon dioxide extraction uses carbon dioxide to extract essential oils. It is an expensive method of extracting essential oils, using both high pressure and low temperature to extract the essential oil from the plant material. It is said that carbon dioxide extraction produces an essential oil which is closer to the essential oil present in the plant (remember that the 'essential oil' obtained through distillation is not the same as the essential oil present in the plant; chemical components are 'altered' through the extraction process). Carbon dioxide extraction does not leave a trace of carbon dioxide in the resulting essential oil and essential oil suppliers are marketing these essential oils as 'pure'; however, the essential oils obtained through carbon dioxide extraction are usually more expensive.



Personally, I have traditionally used distilled or expressed essential oils for pure aromatherapy use - until now. If research continues into the newer methods of hydro-diffusion and carbon dioxide extraction and I am convinced these essential oils are also pure, and can be bought at a reasonable price, I may consider using them in the future...

The Extraction of Essential Oils by Distillation and Expression

Photo of a Simple Homemade Still

For anyone who studies essential oils, distillation is probably the most familiar method of extracting essential oils from plant material; however, not all essential oils can be steam distilled. Most citrus oils, for example, are expressed. So what does 'distilled' and 'expressed' mean? And why are there different methods of extracting essential oils?

Essential oils can be extracted in the following ways:

- Distillation - the most common method of extracting essential oils and a method which has been used for centuries essentially. Plant matter which is steam distilled is in placed in a still, heated and the essential oils (the 'aroma' molecules of the plant) evaporate into the steam. The molecules are then carried along a pipe and when they start to cool (as the pipe passes through a cold water vat) the molecules form into liquid - the essential oils. The essential oils can be separated from the water, as the essential molecules either "sink or float' on the water.


Distillation is used to extract essential oils from the sacs stored in the leaves, roots, seeds and flowers of plants. Aromatherapy and Botany explains more of the storage of essential oils by plants. Some plants have no difficulty producing a large quantity of essential oil in one batch, others are extremely difficult to extract from with minute quantities of essential oil produced in a single batch.

- Expression - citrus fruits are usually expressed to extract essential oils. Essential oils are located in the rind of the fruit and need to be 'squeezed' out - a bit like when you peel the orange and the juice is 'squeezed' out of the fruit, except it is the rind which is expressed in the case of the majority of the citrus essential oils. The problem with expressing pure essential oils from citrus oils is that, in today's world, many fruit trees are chemically sprayed, 'contaminating' the rind of many citrus fruits. For this reason, many aromatherapists prefer to use organic or naturally grown fruits for essential oils (although these terms can be 'open to interpretation' sometimes too!)

Newer methods of extracting essential oils include Carbon Dioxide Extraction (CO 2 essential oils) and Perculation which is coming up next...

Do you have any comments to add on my post on the extraction of essential oils? Add you comments below if you do!