Essential Oil Extraction Processes

Distillation

Steam Distillation

The majority of essential oils available today are extracted using a steam distillation process. It's the oldest form of essential oil extraction and is believed by many to be the only way oils should be extracted. The process really is quite simple and as long as this extraction process is closely monitored, the steam will remain at a temperature that won't damage the plants.

The desired plant material is placed onto a still. A still is a specialized piece of equipment that is used in the distillation process. It consists of a vessel into which heat is added and a device that is used for cooling. The plant is first placed into the vessel. Next steam is added and passed through the plant. The heat from the steam helps to open the pockets of the plant that contain the plant's aromatic molecules or oils. Once open, the plant releases these aromatic molecules and in this state, the fragrant molecules are able to rise along with the steam.

The vapors carrying these molecules travel within a closed system towards the cooling device. Cold water is used to cool the vapors. As they cool, they condense and transform into a liquid state. The liquid is collected in a container and as with any type of oil/water mixture, it separates. The oils float towards the top while the water settles below. From there, it's a simple matter of removing the oils that have been separated. These are the highly condensed, aromatic oils used in aromatherapy.

The water is not discarded, however. The water, which also contains the plant's aroma along with the other parts of the plant that are water soluble, are the hydrosols - a milder form of the essential oils. These, too are also used in aromatherapy.

When steam is used, it's created at a pressure higher than that of the atmosphere. The boiling point is above 100 degrees Celsius and creates an extraction process that is safe and fast. If the temperature is allowed to become too hot, however, the plant material as well as its essential oils can easily become damaged.

Water Distillation

Water distillation involves placing the desired plant material in a still and then submerging it in water. The water is then brought to a boil. The heat helps open the pockets containing the plant's aromatic molecules so they can be extracted. The vapors cool and condense, the essential oils separate from the water and they're collected.

The water in this case provides protection for the plant because it acts as a barrier. Less pressure is used as well as a lower temperature than that which is used in the steam distillation method. This extraction method works well with plants that cannot tolerate high heat.

Other distillation methods

Hydro distillation is similar to steam distillation. The only difference is that instead of introducing the heat from the bottom and up through the still, as happens in steam distillation, the heat passes into the still from the top. It's cooled from below, which makes collection of the essential oils easier. This method actually results in a higher yield of essential oils because less steam and consequently less processing time are involved.

In a water/steam combination distillation method, plant material is submerged into heated water and steam is forced through the water, opening the pockets containing the aroma molecules. When cooled, the essential oils condense and are collected as described above.

Expression

It's true that essential oils are an essential part of aromatherapy. But contrary to what some people think, the term 'essential' doesn't mean essential as in 'being a necessary part of'. Instead, essential oils are the oils extracted from the 'essence' of a plant - those parts that contain the plant's aroma molecules.

Using different methods of extraction guarantees that the highest concentrations of oils can be extracted. Essential oils are gathered from many different types of plants and many different parts of those plants. Flowers, fruits, herbs, stems, roots, leaves, buds, blossoms, seeds, nuts and even tree bark produce some of the most aromatic and therapeutic essential oils. Essential oil extraction methods fall under three main categories: expression, solvent extraction and distillation. The following is an overview of these extraction processes and methods.

Expression

The expression form of essential oil extraction does not involve the use of a heat source. This is the method commonly used to extract oils from the rinds of citrus. In earlier times, rinds were squeezed by hand and a sponge was used to collect the essential oils. The fruit would be removed and then the rinds along with the pith would be soaked in water to make them easier to work with. They'd then be turned upside-down. Turning them upside-down caused the cells containing the oils to break apart. Once broken, the oils would drip out and soak into a nearby sponge. When the sponge became saturated, the oils were squeezed into a container so they could be decanted.

Ecuelle a Picuer

Another expression method involved sticking pins into the skins of fruit for the purpose of damaging the cells that contain the essential oils. The apparatus used had a built-in container for collecting the oils and the other parts of the fruit that ended up in the collection area. The final steps involved separating the essential oils and decanting them. This is called the ecuelle a picuer method.

Machine Abrasion

Those were quite laborious processes, and thankfully, technological advances led to the invention of machines to do this type of tedious work. Nowadays, oils from rinds are extracted using centrifugal force. This rapid process is called Machine Abrasion.

Cold Pressed

This form of expression extraction is also used to extract essential oils from nuts and seeds and from the rinds of citrus. Mechanical pressure is used to force the oils out. The oils extracted contain water, but this water will, in time, evaporate, leaving just the essential oils. The downside of using this extraction method is that the cold pressed oils spoil more quickly than those extracted using other methods. That's why, to eliminate waste, it's important to purchase these essential oils in small quantities.

Solvent Extraction

Some plant material cannot tolerate the heated forms of extraction such as steam distillation. High heat damages these plants and once damaged, their essential oils too are damaged and are no longer able to be extracted. For these plants, as well as others, solvents such as ether, ethanol, methanol, hexane, alcohol and petroleum are used instead. The problem with using solvents to extract essential oils is that most of the time, residual solvents or impurities remain in the end product. Because they're impure, those true to aromatherapy refuse to use them.

As mentioned above, there are times when solvent extraction makes sense. This process involves a lot of chemistry and is somewhat confusing to understand but in general it is as follows.

Plant material is first washed in a bath of hydrocarbon solvents. This process dissolves the necessary plant materials including the aromatic molecules, waxy matter and pigment and the dissolved matter mixes in with the solvent. The solvent mixture is then filtered and distilled using low pressure. After distillation and further processing, either a resin or a concentrated concrete remain. Additional processing using alcohol helps extract the essential oils.

This is a very fast and cost-effective method of essential oil extraction, but there is a downside. With solvent extraction, residual solvents remain and their presence can cause problems if used by individuals with allergies or sensitive skin. That's another reason why essential oils extracted using solvents are used in the manufacturing of perfumes and fragrances, not in aromatherapy or skin care products.

Super Critical Carbon Dioxide (CO2) Extraction

The end result of super critical carbon dioxide (CO2) extraction - one of the newest extraction technologies - is a super-concentrated, high-quality version of essential oil. This rapid extraction method uses lower temperatures and higher pressure to transform carbon dioxide, a gas, into a liquid. It's an inert solvent meaning that it's non-reactive and therefore cannot form another chemical compound. When the extraction process is complete, the carbon dioxide is returned back to a gaseous state therefore, no residual remains. All that is left is pure essential oil.

Although this technology produces one of the purest forms of essential oil, it is not yet widely used. The equipment needed for this extraction process is very expensive, which keeps production costs high. And because production costs are high, so too are the costs of the essential oils that are produced via carbon dioxide extraction.

Maceration

With this essential oil extraction method, hot oil is used as a way to rip apart cell membranes. The plant material is first saturated with hot oil and allowed to soak until the cell membranes rupture. As they break apart, essential oils are released into the oil in which the plant material is soaking. When the release period is complete, the plant material is removed from the oil. The oil that remains then gets decanted.