Solvent extraction is used to extract Essential Oils from plants that cannot withstand the high heat used in steam distillation. Very delicate aromatics, Jasmine, Linden Blossom, etc can not survive the process of distillation. To capture their magical aromas, a process of solvent extraction is used. For some plants, the intense heat damages them so, that the essential oils are unusable therefore, they must be extracted via other means.

For essential oil solvent extraction methods one might use alcohol, hexane, ethanol, ether, methanol or even petroleum to coax the oils out of the plant. Most people don’t approve of these methods, however, because some of the solvent will end up in the final essential oils that are consumed. This makes for an impure oil, that aromatherapy and healing purists won’t tolerate.

An extracting unit is loaded with perforated trays of blossoms. The blossoms are washed repeatedly with a solvent (usually hexane.) The solvent dissolves all extractable matter from the plant whch includes non-aromatic waxes, pigments and highly volatile aromatic molecules. The solution containing both solvent and dissolvable plant material is filtered and the filterate subjected to low pressure distillation to recover the solvent for further use. The remaining waxy mass is what is called the concrete and it contains in the case of Jasmine grandiflorum as much as 55% of the volatile oil.

The concentrated concretes are processed further to remove the waxy materials which dilute the pure essential oil. To prepare the absolute from the concrete, 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 is the wax an efficient separation of the two takes place. But 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 precipates out. As a final precaution the purified solution is cold filtered leaving only the wax-free material (the absolute.)

This solvent extraction actually yields three usable products; first the concrete (as in rose concrete, my favorite solid perfume), the precious absolutes, and the floral waxes, for addition to candles, thickening creams and lotions as a softly floral scented alternative to beeswax.

During solvent extraction, the plant is put into a bath of solvents which dissolves the plant material. This liquid mixture now contains the essential oils and other parts of the plant and is filtered and goes through a low pressure distillation process. Alcohol is then used to help separate out the essential oils.

This method is fast and inexpensive, but since it produces a non pure oil, it is mostly used in oils that are put into perfumes and not on the skin. The other problem is that anyone allergic to the solvents will have a reaction if rubbed on the skin.

A new essential oil solvent extraction technology called Critical Carbon Dioxide Extraction will yield a highly concentrated essental oil. When CO2 (carbon dioxide) is subjected to high pressure, the gas turns into liquid. This liquid CO2 can be used as a very inert, safe, "liquid solvent." which will extract the aromatic molecules in a process similar to that used to extract absolutes The advantage, of course, is that no solvent residue remains, since at normal pressure and temperature, the CO2 simply reverts to a gas and evaporates. It produces a high quality, pure essential oil but is very expensive at this time.

CO2 extraction has given us essences of some aromatics that don't yield essential oils, Rose Hip Seed, and Calendula, for examples. Iif the same essential oil is available both as a steam distilled EO 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.

Another method, called maceration, is sometimes used with good results. This method of extracting essential oils involves soaking the plant in hot oil. This causes the cell membranes to burst and the essential oil to leak out. Then the plant itself is removed and the oil is decanted.