Essential oils are substances extracted from plant matter using a variety of extraction methods. Many parts of the plant can be use in the extraction process, from flowers, fruit, and seeds to twigs, roots, leaves, or resin. The final essential oil is a concentrated liquid that takes on the properties of the plant from which it came; however, many factors can affect the quality of the final oil.

Methods of Extraction

Some of the more popular extraction methods are listed below:

Steam Distillation

The most popular method of extraction is steam distillation. This method involves steaming plant matter for a length of time, under pressure and a specific temperature best suited for releasing the oil. The distillate from steam distillation is collected as the essential oil. The water in which the herbs are steeped is known as floral waters, or hydrosols, a less concentrated product than essential oils, still containing some properties of the plant.

Cold Pressing

Cold pressing is another extraction method which is most often used to release the oils from citrus rinds. Because this method requires mashing rinds in water, it is important to seek organic options for cold pressed essential oils.

Solvent Extraction

Some essential oils, such as jasmine and rose, are produced by mixing the delicate flowers with a solvent. Purists do not consider solvent extractions to be true essential oils. Also referred to as absolutes, aromatherapists generally do not recommend these types of essential oils for use on pregnant women and children.

No matter which extraction method is used, essential oils are considered “pure” after completion of extraction.

Essential Oil Quality

Therapeutic content and quality of essential oils are affected by several factors. Some of these include:

  • Soil quality in which plants are grown
  • Climate where plants are grown, including altitude, rain fall, and temperature
  • Harvesting method
  • Storage conditions of plants prior to extraction, including time before processing and humidity levels
  • Parts of the plants used – leaves, roots, resin, etc.
  • Type of distillation equipment used (steel or copper)
  • Storage conditions after distillation, including temperature control
  • Alteration of the pure essential oils
  • Storage time before purchase

Essential Oil Chemotype

Depending on the different environments in which some plants are grown, they may generate different chemical constituents. These different chemical types of the same genus and plant are referred to as chemotypes.

Not all plants have different chemotypes. For those that do, it can be important to know the difference. Therapeutic properties and safety considerations can be different for different chemotypes of the same plant.

How to Identify a Chemotype

Identifying a chemotype is easy. Look for a “ct” designation after the botanical name, for example:

Rosmarinus officinalis ct. camphor

“Camphor” is the specific chemotype of Rosemary.

Not all companies provide chemotype information on the bottle. When in need of a specific chemotype due to its therapeutic properties, check the company's website first. If the inforamtion is not listed, contact the company. Reputable companies will know the importance of this information and should be happy to share it with customers.


About the Author: Lea Harris is a Certified Clinical Aromatherapist graduate from Aromahead Institute, with more than 400 hours of study. UsingEOsSafely.com and its sister website, LearningAboutEOs, is home to educational advice and information about using essential oils safely.