Methods of Extracting Essential Oils
Thanks to Ben Alkire and Christopher McMahon of White Lotus Aromatics for providing much of the information below.
The vast majority of true essential oils are produced by distillation. There are different processes employed in distillation, but in all of them, water is heated to produce steam which carries the most volatile chemicals of the aromatic material with it. The steam is then chilled (in a condenser) and the resulting distillate is collected. The essential oil normally floats on top of the hydrosol (the distilled water component) and may then be separated off. To read more about hydrosols, please click here.
Steam Distillation:True steam distillation uses an outside source of steam which pipes steam into the distillation unit, sometimes at high pressure. The steam passes through the aromatic material and exits into the condenser.
Hydrodistillation:The botanicals are fully submerged in water, producing a “soup,” the steam of which contains the aromatic plant molecules. This is the most ancient method of distillation and the most versatile. It’s the method most often used in undeveloped countries. The risk is that the still can run dry or overheat, burning the aromatics and resulting in an essential oil with a burnt smell. Hydrodistillation seems to work best with powders (e.g. spice powders, ground wood, etc.) and very tough materials like roots, wood, or nuts.
Water and Steam Distillation:A water and steam distillation arrangement can be compared to a kitchen steamer basket, with the botanicals supported in a “basket” over boiling water, thus exposing the plant material only to the rising steam vapors. This is the best method for distilling leafy materials, but doesn’t work well for woods, roots, seeds, etc.
Absolutes and Concretes: Solvent Extraction
Very delicate aromatics such as Jasmine or Linden Blossom cannot survive the process of distillation. In order to capture their magical aromas, a process of solvent extraction is used. An extracting unit is loaded with perforated trays filled with blossoms. The blossoms are washed repeatedly with a solvent (usually hexane). The solvent removes all extractable matter from the plant which includes non-aromatic waxes, pigments, and highly volatile aromatic molecules. The solution containing both solvent and dissolvable plant material is filtered, and the filtrate is subjected to low pressure distillation to recover the solvent for further use. The remaining waxy mass is called the ‘concrete’ and it contains (in the case ofJ. grandiflorum)as much as 55% of the volatile oil.
The concentrated concrete is processed further to remove waxy materials which dilute the pure essential oil. To accomplish this, the waxy concrete is warmed and stirred with alcohol (usually ethanol). During the heating and stirring process, the concrete breaks up into minute globules. Since the aromatic molecules are more soluble in alcohol than in the wax, an efficient separation of the two takes place. However, along with the aromatic molecules a certain amount of wax also becomes dissolved and this can only be removed by agitating and freezing the solution at very low temperatures (around -30 degrees F). In this way most of the wax precipitates out. As a final precaution, the purified solution is cold filtered leaving behind only the wax-free aromatic material (the absolute).
This solvent extraction actually yields three usable products; the concrete (as in rose concrete, my favorite solid perfume), the precious absolutes, and the floral waxes. The waxes can be used in candles, thickening creams, and lotions as a softly floral scented alternative to beeswax.
Carbon Dioxide Extraction
When CO2 (carbon dioxide) gas is subjected to high pressure, it turns into liquid. This liquid CO2 can be used as a very inert, safe, “liquid solvent” which will extract aromatic molecules from plant material in a process similar to that used to extract absolutes (above). The advantage is that no solvent residue remains, since at normal pressure and temperature, the CO2 simply reverts to a gas and evaporates. CO2 extraction has given us essences of some aromatics that don’t yield essential oils, such as Rose Hip Seed and Calendula. In our opinion, if the same essential oil is available both as a steam distilled essential oil and a CO2 extracted essence, the CO2 seems to have a richer, more intense scent, since more of the aromatic chemicals are released through this process. For more details of this process and the different types of CO2 extracts please click here.
Cold Pressing (Mechanical Extraction)
We are all familiar with the spray of orange essential oil that is released by scoring or zesting the skin of the fruit. The cold pressed citrus oils are produced just this way, by machines which score the rind and capture the resulting oil. Although many citrus oils are also produced by steam distillation, they seem to lack the vibrancy of the cold pressed oils.
This extraction method uses a new type of benign gaseous solvents. In the late 1980s, Dr. Peter Wilde first recognized the unique properties of these solvents for the extraction of aromatic oils and biologically active components from plant materials for use in the food, pharmaceutical, aromatherapy, and perfume industries. “Florasol” (R134a), is the solvent upon which the process is based. Extraction occurs at or below ambient temperatures; hence there is no thermal degradation of the products. The extraction process utilizes the selectivity of the solvent and produces a free-flowing clear oil free of waxes.
At the current time, the sole US distributor of Dr. Wilde’s Florasols is The Essential Oil Company. However, we are researching a source for bulk Florasols at a more appealing price.