There’re a great number of essential oil manufacturers out there and the quality of the oils can vary a lot. But the ways the makers make their essential oils come down to just a handful of methods.
Method 1: Distillation
Distillation is the most common way of making essential oils. There’re four kinds of distillation: water distillation, water-and-steam distillation, steam distillation and hydrodiffusion distillation.
No matter which distillation approach is used, the process involves heating the plant materials till the essential oil molecules vaporize and go up into a pipe, together with the steam from heated water.
The vaporized essential oil molecules and steam then travel together into a cool container and condense back into liquid form. Since oil and water don’t mix, it is easy to separate the two and scoop out the essential oil. The water, which would have a bit of essential oil in it, is often used to make hydrosols.
Method 2: Expression (Cold-pressing)
Expression is only used for citrus fruits (e.g. orange, lemon, lime).
What happens is a machine will poke tiny holes in the rinds (or peels) and press them to squeeze out the essential oil molecules. Some juice and non-soluble components such as natural waxes will also be squeezed out.
The mixture is then allowed to stand till the oil rises to the top and can be scooped out. No heat is used, hence the term “cold-pressing”.
This method can be used on citrus fruits because (a) peels are tough, and (b) the essential oil molecules of citrus fruits are close to the surface of the peel and are therefore easy to extract through pressing.
You can even do this at home yourself if you want to. That is, if you have strong hands and don’t mind squeezing citrus peels all day long. Squeeze the rinds hard and drops of essential oil goodness will drip out. Collect and store them in dark glass containers and you can use the oil when you want.
Now, if you really don’t mind the hard work (and cramped hands) and want to try doing this at home, do use organically-grown citrus fruits. Otherwise, you’ll be collecting the pesticides as well as the oil, which obviously isn’t great for your health.
Note also that cold-pressed essential oils have a pretty short shelf life. So store them in a cool, dark area, and before using the oils, check to make sure that they have not gone rancid.
Method 3: Solvent Extraction
There’re some plant materials which are too delicate to go through distillation (high heat) or cold pressing (high stress). These are usually flowers such as jasmine, gardenia and narcissus. For such plant materials, solvent extraction is used instead to extract the essential oils.
As the name implies, an oil-soluble hydrocarbon is used as a solvent. Common solvents used are hexane, methanol and ethanol.
The plant materials (usually flower petals) are soaked in the solvent to draw out the essential oil molecules. Some other stuff will also be drawn out, such as chlorophyll, some plant tissues and fats and waxes. This mixture is called “concrete”.
Yup, the mixture has the same name as the stuff that’s used to make roads and houses!
But fear not, you’ll not be slathering concrete on your face or wrecking your diffuser to diffuse concrete. The concrete mixture does go through a second step.
It is mixed with alcohol to draw out and isolate the essential oil components, and this final product is called “absolute”. For more details on absolutes, see this post.
Method 4: Carbon Dioxide Extraction
Also called Hypercritical CO2 Extraction, this is a relatively new method. It’s pretty expensive and therefore not very common yet, though this may change in the future.
This method involves putting carbon dioxide through high pressure to turn it into a dense quasi-liquid, something that has liquid properties while in gaseous state. This quasi-liquid go through the plant materials and draw out the essential oil elements. After that, the pressure is reduced, the carbon dioxide turns back into gas and what remains is the essential oil components.
Although expensive, this method may become more widespread in the future because it can produce “purer” or ” more complete” essential oils.
For instance, essential oils made by solvent extraction will have a little solvent left in the oil. The proportion is very, very tiny (less than 0.0001%) but there is a bit. On the other hand, there’ll be no solvent (i.e. carbon dioxide) residue at all in the essential oils made by carbon dioxide extraction.
Essential oils made by carbon dioxide extraction can also be more similar to the original plant than those made by distillation. This is because for some plants, certain components of the essential oil cannot be extracted by distillation. For example, some medical properties of frankincense cannot be captured by distillation, but can be obtained through carbon dioxide extraction.
Method 5: Enfleurage
This is a traditional method used in the past to make perfumes in Grasse, France. Grasse was the perfume capital of the world years ago.
Flowers were handpicked and soaked in oils and animal fats to draw out the essential oil. Today, this method is hardly used and it has pretty much been replaced by solvent extraction.
Now, if you’ll like to learn more about how these extraction methods affect the purity of essential oils, turn to this post.