How Essential Oils Are Made
A herbal extract is produced when a botanical material is introduced to a solvent in which some of the plant material components dissolve. Ultimately, the solvent becomes infused with the botanical materials that it has pulled from the source plant, and this is what is referred to as the “extract.” The solution that remains at the end of the process can be liquid, or the liquid can be removed to turn the remnants of the botanical into a solid. The solvents can act as preservatives or as agents that help plant cells to break down and release their contents.
Steam Distillation is the most popular method used to extract and isolate essential oils from plants for use in natural products. This happens when the steam vaporizes the plant material’s volatile compounds, which eventually go through a condensation and collection process.
This method employs food grade solvents like hexane and ethanol to isolate essential oils from plant material. It is best suited for plant materials that yield low amounts of essential oil, that are largely resinous, or that are delicate aromatics unable to withstand the pressure and distress of steam distillation. This method also produces a finer fragrance than any type of distillation method.
Through this process, the non-volatile plant material such as waxes and pigments, are also extracted and sometimes removed through other processes.
Once the plant material has been treated with the solvent, it produces a waxy aromatic compound called a "concrete." When this concrete substance is mixed with alcohol, the oil particles are released. The aforementioned chemicals used in the process then remain in the oil and the oil is used in perfumes by the perfume industry or for aromatherapy purposes.
Essential oils derived from the supercritical CO2 extraction of herbs are similar to the oils produced through distillation in that they can be used in aromatherapy and natural perfumery.
Oils derived from steam distillation vary in their qualities depending on the temperatures, pressures, and length of time applied for the process. The CO2 extraction process might thus produce higher quality oils that have not been altered by the application of high heat, unlike the steam distillation process. In CO2 extraction, none of the constituents of the oil are damaged by heat.
Thus, the difference between traditional distillation and supercritical extraction is that instead of heated water or steam, CO2 is used as a solvent in the latter method. The supercritical extraction process operates at temperatures between 95 to 100 degrees F whereas steam distillation operates at temperatures between 140 to 212 degrees F.
In steam distillation, the molecular composition of both the plant matter and the essential oil are changed due to the temperature applied. On the other hand, a CO2 extract is closer in chemical composition to the original plant from which it is derived, as it contains a wider range of the plant’s constituents.
For example, CO2 Extraction of German Chamomile flowers yields a green extract, because the absence of heat means it was not altered from its natural state or “denatured.” The resulting extract is thus more similar in composition to the original flower than the distilled essential oils is.
CO2 extracts are usually thicker than their essential oil counterparts and often give off more of the aroma of the natural herb, spice, or plant than a distilled essential oil. CO2 extracts have been said to contain more plant constituents than the amount extracted from the same plant using steam distillation.
Macerated oils are also referred to as infused oils. They are created when carrier oils are used as solvents to extract therapeutic properties from plant material. The benefit of a macerated oil above a distilled oil is that more of a plant’s essence is captured in the oil, because it captures heavier, larger plant molecules than the ones captured in the distillation process. This keeps the product closer to retaining more of the plant’s valuable offerings.
The ideal plant material to be infused will be harvested so that it is as dry as possible, as any plant moisture will cause the oil to become rancid and will encourage microbial growth. Adding 5% of Vitamin E oil or Wheatgerm oil (which is high in Vitamin E) will prevent rancidity.
Enfleurage is not commonly used today, but it is one of the oldest methods of essential oil extraction that implements the use of fat. By the end of this process, either vegetable fat or animal fat becomes infused with the flower’s fragrance compounds. The fats that are used are odorless and solid at room temperature. The enfleurage process can be done either “hot” or “cold.” In both instances, the fat that is saturated with fragrance is called "enfleurage pomade."
Delicate flowers such as roses and orange blossoms would clump together when introduced to steam in the distillation process, so the most effective method of extraction in this situation is to submerge fragile plant material in pure boiling water instead. The water protects the extracted oil from overheating. The condensed liquids cool down and separate from each other. The remaining water, which can sometimes be fragrant, is referred to by several names including hydrolate, hydrosol, herbal water, essential water, floral water, or herbal distillate.
This method is also called Expression or Scarification and is used for citrus peels in particular. The whole fruit is placed in a device that mechanically pierces it to rupture the essential oil sacs, which are located on the underside of the rind. The essential oil and pigments run down into the device’s collection area. The whole fruit is pressed to squeeze out the juice and the oil. The oil and juice that are produced still contain solids from the fruits, such as the peel, and must be centrifuged to filter the solids from the liquids. The oil separates from the juice layer and is siphoned off into another receptacle.