Extraction Methods of Essential Oils
Therapeutic-grade essential oils are most often extracted via a low-heat steam distillation process in which steam is circulated under pressure through plant material liberating the essential oils into the steam. As the steam mixture cools, the water and oils naturally separate and the oil is collected in its pure form.
To ensure the highest quality oil extract of correct chemical composition, temperature and pressure must be monitored very closely. Too little heat and pressure will not release valuable oil while too much can change an extract's composition and potency. Temperatures for steam distilling usually range between 140-212 degrees Fahrenheit. Since different plants require different pressures, times, and temperatures, using this particular distillation method makes it possible to adjust the temperature based on the plant type, making it a very effective and precise way to obtain the purest compounds.
Just as important as the carefully controlled extraction process is the careful selection of the correct plant and plant parts. Harvesting at the right phase in the life cycle of the plant is also required for a successful extraction. This complex process is as much an art form as it is science, and demands experienced growers and distillers work together to ensure a quality product.
Cold Pressing or Expression
While steam distillation is by far the most common method of extraction, a select few plants, many of them in the citrus family, are cold pressed in a process of compression in which the oil is squeezed from the plant. Essential oils extracted in this way are called expressed oils. In the case of citrus essential oils, it is the rind of the fruit which is pressed. doTERRA uses expression to extract all of its citrus oils, such as Wild Orange, Lemon, Lime, Bergamot, and Grapefruit, from the rind.
Whereas essential oils can typically be produced through steam distillation, absolutes require the use of solvent extraction techniques or more traditionally, through enfleurage. A very few plant oils are extracted this way, using solvents that bind with the oils which are eventually removed from the final product. Solvent extraction is a method of extracting essential oils that dominates the perfume industry.
The enfleurage method of oil extraction falls in to the category of an 'absolute' and is one of the oldest methods of extracting essential oils. It is rarely used these days because of its high cost. It involves placing the flower petals on a layer of glass that is first spread with a thin layer of fat called 'chassis'. The volatile oil diffuses into the fat, then the fat is collected and the oil is extracted from the fat using alcohol. Once the alcohol evaporates what is left behind is called the absolute. As you can imagine, this is a very time consuming process, but long ago it was the only way to extract delicate flowers like Jasmine!
In modern times, a chemical solvent is first added to the plant material to help extract the non-polar compounds. This solution is filtered and concentrated by distillation to produce a waxy mass called concrete. Then the more polar, fragrant compounds are extracted from the concrete into ethanol. When the ethanol evaporates, an oil—the absolute—is left behind. This production method may leave trace amounts of solvents in the absolutes.
Although the amount of remaining solvent is considered tiny in carefully extracted absolutes, many absolutes are considered undesirable for therapeutic use. So, while steam distilled and expressed essential oils are preferred within the scope of holistic therapy, absolutes do hold their place within holistic aromatherapy and natural fragrancing applications.
As with steam distilled essential oils, absolutes must be used with care, respect and knowledge. Essential oils can offer great benefit when taken internally by those properly educated in the internal application of certified pure therapeutic grade essential oils, however, absolutes are generally avoided for internal use because of the trace solvent they contain.