Essential Oils Extraction Methods
How an essence is extracted, depends solely on the plant type. There are several basic types of extraction commonly used today. They are steam distillation, water distillation, cold press expression, solvent(chemical) extraction, and CO2 extraction. Maceration and Enfleurage are older less commonly used methods. The following is a brief description
Steam distillation is the most common type of extraction. It is done by filling a stainless steel* still with parts of the CTEO (Chemo typed Essential Oil) plant to be distilled. A pure water source, like spring water, is heated and steam passes into the still with the plant parts at low pressure (0.05 to 0.10 bar). Here the plant essence burst from its specialized cell reservoirs infuses with the steam and passes from the still into a condensing coil cooled with water.
The water and plant essence flow together into a sealed flask and separate. Plant essence is the valuable phytochemicals of the plant we call essential oil. It represents the components of the plant not soluble in water. They are lighter than water and therefore float to the top.
Next, the essential oil is siphoned off into a cooled, stationary, pressure-sealed tank for filling and distribution. The water that remains is called a hydrosol. Hydrosols contain some residual plant essence as well as all the plant’s water-soluble components. Hydrosols have wonderful hydrating, toning, and healing properties for face skin and hair.
* Note: Stainless steel is a must to avoid the formation of oxides
*Note: Spring water should not contain any calcium. Calcium will cause build-up on the inside of the distillation tank which must be removed through a descaling process. Residues must then be removed. These are costly additions to essential oil extraction.
Water distillation is similar to steam distillation. It is used primarily for plant parts that are delicate and need water to suspend them in a more even fashion (i.e. Rose petals). Parts are placed in a distillation tank, immersed in water, and heated to boiling. The resulting steam flows into a cooling coil, condenses into a flask, and sealed. The lighter (usually) essential oil floats on top and is decanted into a cooled, pressurized holding tank.
Expression or Cold Press method of extraction is done mostly on citrus fruits like orange and lemon. The extraction can be done manually or mechanically. In both, the release of essence (essential oil) is accomplished by abrasion and laceration of the skin or rind.
There are two ways to separate the essential oil in this method. A more traditional Sponge method and a more modern Mechanized method.
- Sponge Method – Abrasion/laceration of the fruit results in a three-phase liquid after resting for a short while. The three layers are oil(essence), emulsion, and water. Once the layers separate the pure essential oil on the top is easily siphoned and collected. The middle layer is a relatively stable mixture of water and oil (essence) called an emulsion. The bottom layer is mostly water which can be discarded. retrieve the vital oil from the middle layer a sponge or wool is used to absorb the liquid. It is then pressed, and the resulting oil collected. This method is costly, lengthy, and predisposes the essence to oxidation.
- Mechanized Method- During the abrasion phase, water rinses the essences from the fruit. The result is a two-phase liquid. The top layer is an essential oil emulsified with non-volatile materials and plant debris. The bottom layer is water which is discarded. After the large debris has been filtered, the emulsion is put through a process called centrifugation. Filtration and centrifugation are complex processes in which the integrity of the essence must be considered. During these processes heat, exposure to air, and acidity of the emulsion can cause damage to the aromatic volatiles (oil/essence). These harmful processing factors are mitigated by proper cooling and airtight storage of the emulsion as well as pressurized centrifugation.
Solvent extraction is used primarily for the perfume industry. This method is the least desirable for aromatherapy usage as chemical residues of solvent, alcohol, and waxes remain in the finished product and can cause allergies or affect the immune system. Plant parts that are resinous, of low yield, or too delicate for steam extraction are candidates for solvent extraction.
Solvent extraction occurs in three basic phases:
- Plant parts containing the desired essence are mixed with food-grade solvents such as ethanol, methanol, and hexane. The resulting mixture is called a concrete and contains the essential oil and other non-volatiles from the plant like waxes and pigments.
- The concrete is then mixed with alcohol releasing the oil from the mixture.
- The alcohol/oil mixture is vacuum distilled and condensed.
Most of the alcohol and solvent remaining in the oil are driven off during the last step. The final product is called an absolute.
Plant parts to be extracted are placed in a pressurized container with Carbon Dioxide (CO2). The pressure is raised to around 74 bars (73 atm or 1000 psi) causing the carbon dioxide to liquefy. In this state, the essential oil is released from the plant parts mixing with the carbon dioxide. The pressure is then lowered back to normal and the carbon dioxide returns to a gas phase leaving the extracted oil. This method has the advantage over solvent extraction in that there is no chemical residue left behind.
Maceration is the process by which the plant parts of a desired essential oil are infused with a carrier oil. The maceration process takes about a week and requires the plant parts to be dried and crushed. The resulting plant powder is added to a closed vessel and the carrier oil (solvent) is added. The vessel is periodically rotated. After the infusion, the mixture is strained, filtered, clarified, and stored in airtight containers. Sometimes vitamin e is added to protect against rancidity.
Enfleurage is an old extraction method and similar to maceration. It is also in an infusion of plant essence into a a carrier oil. Actually, fat would be more accurate. Either vegetable or animal fat is spread onto a glass plate. Flower petals of the desired essential oil to be infused are placed into the fat and another glass plate is placed on top.
Hot or cold fat can be used. The petals are left to infuse for 1 to 3 days or even a couple of weeks depending on the saturation of fragrance desired. The final product is called a pomade. Then alcohol is used to strip the essence (aromatic volatiles) from the fat. The alcohol evaporates leaving behind the essence. This liquid is called an absolute. It is said to be more concentrated and closer to the aroma of the plant when more of the plant is used. Absolutes are used mostly in the perfume industry.
5. https://www.pranarom.com/en/scientific-aromatherapy/distillation-and-expressionessential oils
Extracting Essential Oils