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.
A hydrocarbon solvent (usually hexane) is added to the botanical material to help dissolve the extractable matter from the botanical material which includes non-aromatic waxes, pigments and highly volatile aromatic molecules. When this solution is filtered and then the filtrate is subjected to distillation at low pressure, a substance containing resin (resinoid), or a combination of wax and essential oil (known as concrete) is left.
The concrete is further processed 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). When we heat and stir the concrete, it breaks up into minute globules, and separation takes place as aromatic oil is more soluble in alcohol than that in wax. But along with the aromatic molecules a certain amount of wax is also dissolved and this can be removed only by agitating and freezing the solution at very low temperatures (around minus 35 degree celsius). In this way most of the wax precipitates out. As a final precaution the purified solution is cold filtered leaving only the wax-free material (the absolute) i.e. the essential oil.
This solvent extraction actually yields three usable products; first the concrete (as in rose concrete, my favorite solid perfume), the precious absolutes i.e. the oils, and the floral waxes, for addition to candles, thickening creams and lotions as a softly floral scented alternative to beeswax.
Although more cost-efficient than enfleurage, solvent extraction is more expensive than steam distillation so it is reserved for costly oils which cannot be distilled.
This is not considered the best method for extraction of essential oils, as the solvents can leave a residue behind which could cause allergies and effect the immune system, but it's great for making resins for this very reason.