Understanding Different Forms of Essential Oil Extraction

Extracting clove oil in a funnel

Did you know that there is an international definition of essential oils? The very formal definition according to ECHA (European Chemicals Agency) is, “An essential oil is defined as a volatile part of a natural product, which can be obtained by distillation, steam distillation or expression in the case of citrus fruits. It contains mostly volatile hydrocarbons. Essential oils are derived from various sections of plants. The oil is ‘essential’ in the sense that it carries a distinctive scent, or essence of the plant.” 

More importantly, that definition dictates that essential oils are extracted by certain methods. As we try to understand the distinction between an essential oil and an aromatic extract, you will see that the name of the product reveals the method of extraction. 

An essential oil is not an absolute, nor a C02 (Carbon Dioxide) Extract. Essential oils, absolutes, and Co2 extracts come from various parts of plants and trees: flowers, leaves and twigs, heartwood, bark, whole herbal plants, aerial parts of plants, roots, rhizomes, and resin. The extracts are in secretory sacs of these parts and the method of extraction breaks open these sacs to release the oil, absolute, or extract.

Okay, you say… So what?

So…

What does it mean to be an essential oil?

In order for something to be considered an essential oil, that botanical product has to be extracted through distillation or expression. And distillation today means there are water and steam involved in the process. There is also a method called dry distillation but that is not common.  Lastly, there is Expression which is otherwise known as cold pressing.

  • Steam Distillation is when the botanical material is held above the water.  Never touching it. Like if you were steaming vegetables.
  • Hydro-distillation is when the botanical material is in the water, like boiling pasta.
  • Combo steam hydro is when the plant material is both in the water and also in the “steamer” part of the still.
  • Dry distillation is the heating of solid materials to produce gaseous products (which may condense into liquids or solids). Ex Cade
  • Expressed – or cold pressing.  This process is for fruit rinds

  A machine generally does the peeling and mashing while water is passed over the material to keep it moving, clean. and cooled down. The water and extra rind material need to be separated from the oil. This is done by first passing the “slough” (extra rind junk, water, essential oil) through a sieve, and then sending it to a centrifuge where it is spun at very high speeds to separate the oil and water.

    So if the name ends in essential oils than you know it was either steam, hydro, dry distilled or cold-pressed!  Pretty awesome, yes?

Another kind of extraction: Solvent extraction 

If a botanical is extracted by a solvent, it is called an Absolute, not an Essential Oil. So, it is Jasmine absolutepink lotus absolute, etc.

Solvent Extraction is a two-step process:

Step 1: Plant material is mashed up and washed in a vat of solvent. The plant material is filtered off, leaving a mixture of the solvent, essential oils, plant waxes, and pigments.  This blend is heated up in a vacuum, creating a “concrete.” This is a solid blob of product that can remain in this state for an extended time.

Step 2: Now the essential oil has to be separated from the other parts of the concrete. Separation is achieved by mixing the concrete with ethanol. By doing this, the waxes congeal and fall out of the blend. The remaining mixture is vacuum concentrated, the alcohol sucked off, and the absolute collected.

Please note: Absolutes will contain some residue from the solvent. Depending on how well the absolute is made, there can be significant solvent left or very small untraceable amounts.

The newer kind of extraction: Carbon Dioxide Extraction

Co2 Extracts – are aromatic extracts extracted by Carbon Dioxide.

Co2 extracts are relatively new in the aromatherapy field. When working with Co2 extracts you will see the terms select, total, subcritical and supercritical. (well get to them, don’t worry)

Carbon Dioxide is unique because its solvency power can change by simply adjusting the temperature and pressure during the extraction.

  • When the pressure and temperature of the CO2 are above 1083psi AND 88F, the CO2 is considered supercritical.  Supercritical fluid has liquid-like density, it exhibits gas-like diffusivity, surface tension and viscosity.
  • If the temperature drops below 88F, the CO2 changes to a liquid and is referred to as subcritical. The CO2 in its subcritical state acts as a solvent and becomes saturated with aromatic constituents. It is then pumped into a chamber with a different temperature and pressure and voilà – the CO2 reverts back into its normal state, leaving behind the aromatic extract. The CO2 is then recycled. (Awesome!!)

So, a CO2-se (select) is extracted at the subcritical state. CO2 Select extracts are similar to essential oils, but usually are much thicker in viscosity. They are like steam/hydro distilled essential oils in application and composition but they contain way more volatile components than steam distilled extracts. Aka – subcritical

A CO2-to (total) extract is produced under high pressure and higher temperature and contains all CO2-soluble lipophilic plant constituents, e.g., essential and fatty oils, carotenoids, lipophilic antioxidants, sterols, tocopherols, other bioactive constituents, resinoids and waxes. This makes the extract very similar to the plant itself. CO2 Totals are generally thick and pasty or even solid. AKA – supercritical.

Think of it like this. Essential oils and absolutes are like a cheese pizza.

CO2 Selects are like a cheese pizza with pepperoni. CO2 Totals are like a cheese pizza with all the toppings.

You can see that you can know the method of extraction used just by the name!  Pretty cool!