How an essence is extracted, depends on the plant type. There are several types of essential oil extraction methods commonly used today. The following is a brief description.
Essential oil extraction methods
Steam Distillation
Steam distillation is the most common type of extraction. The extraction is done by filling a stainless steel* still with the parts of the CTEO (Chemo typed Essential Oil) plant to be distilled. A pure water source, like spring water, is heated and the steam passed into the still with the plant parts at low pressure (0.05 to 0.10 bar). Here the plant essence bursts 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. The plant essence is the valuable phytochemicals of the plant we call essential oil. It represents the components of the plant that are not water-soluble. They are lighter than water and therefore float to the top. The essential oil is then siphoned off into a cooled, stationary, pressure-sealed tank for filling and distribution. The remaining water is called a hydrosol. Hydrosols contain some residual plant essence as well as all the water-soluble components of the plant. 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. 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
Out of all the essential oil extraction methods, water distillation is like steam distillation. In this form of extraction, plant parts that are delicate and need water to suspend them in a more even fashion (i.e. Rose petals), are placed in a distillation tank and immersed in water. The water is heated to boiling. The resulting steam flows into a cooling coil and is condensed into a sealed flask. The lighter (usually) essential oil floats on top and is decanted into a cooled, pressurized holding tank.
Expression
Expression or cold press essential oil extraction methods type is done mostly on citrus fruits like orange and lemon. The extraction can be done manually or mechanically. In both, the release of essence (the volatile aromatics) is accomplished by abrasion and laceration of the skin or rind.
Traditionally, the sponge method has been used in which the resulting liquid is collected (no added water) and allowed to rest. Fairly quickly three phases appear. The top layer is pure essential oil or essence which is easily siphoned off. The middle layer is a relatively stable mixture of water and oil (aromatic volatile) called an emulsion combined with other non-volatile matter and debris. The bottom layer is mostly water which can be discarded.
To 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.
The mechanized way uses water to rinse 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.
In both methods, an emulsion layer is created in which the oil must be separated. After the large debris has been filtered, the emulsion is put through a process called centrifugation. Make no mistake, 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). These harmful processing factors are mitigated by proper cooling and airtight storage of the emulsion as well as pressurized centrifugation.
Solvent Extraction essential oil extraction methods
Solvent extraction is used primarily for the perfume industry (i.e. Jasmine). 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 concrete 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.
CO2 Extraction
In this method, the 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) of pressure causing the carbon dioxide to liquify. 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; the carbon dioxide returns to a gas phase and is eliminated leaving the extracted oil. This method has the advantage over the solvent extraction in there is no chemical residue left behind.
Maceration
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 again rancidity.
Enfleurage
Out of all the essential oil extraction methods this is somewhat outdated, but similar to maceration in that it is an infusion of plant essence into an 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.
This can be done with the fat cold or hot. 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. 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 and is said to be more concentrated and closer to the aroma of the plant as more of the plant is used. Absolutes are used mostly in the perfume industry.
References:
1. https://www.essentialoilmach.com/news/essential-oil-extraction-methods/
2. https://www.medicinalplantsarchive.us/essential-oils-2/methods-of-separation.html
3. http://purenaturalessentialoil.com/pages/Extractionmethod-jasmine.html
4. https://www.newdirectionsaromatics.com/blog/articles/how-essential-oils-are-made.html
5. https://www.pranarom.com/en/scientific-aromatherapy/distillation-and-expressionessential oils
