Absolutes and Concretes: Solvent Extraction
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.
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 J. 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.
http://www.naturesgift.com/extraction.htm
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