Solvent extraction

The flowers are soaked in a volatile solvent, usually hexane, at low temperature. The solvent dissolves the aromatic part together with waxes and pigments.

The solvent is evaporated off completely, leaving a thick waxy mass called concrete. Concrete contains the smell but also plant waxes, so it is not yet usable in perfumery.

The concrete is washed with pure alcohol; the aromatic part dissolves in the alcohol and the wax does not. The alcohol is evaporated off, leaving the absolute — the most concentrated and most expensive of the three forms.

It keeps heavy molecules and the indolic group whose proportions distillation distorts — this is the only commercially viable way left to capture the smell of jasmine at real scale. Enfleurage and tea scenting can also capture it, but one is nearly extinct and the other produces a scented carrier rather than an extract. If you have ever seen cheap, crystal-clear jasmine oil, what you were holding was almost certainly not jasmine.

There is always trace solvent at parts-per-million level. Industry standards set limits for that residue, but there is no way to bring it to zero, so by the narrow definition an absolute is not an essential oil.

A second, less discussed limitation: this method cannot be used for materials you want to eat or drink. Trace hexane acceptable in perfume is not acceptable in food, which is why food flavourings use CO₂ or distillation and rarely hexane.

There is a symmetry worth noticing when this method is set beside enfleurage. Both have a product that stops halfway and a product that goes all the way:

Solvent extraction gives concrete and then absolute. Enfleurage gives pomade and then absolute. In both, the transition is an alcohol wash followed by driving off the alcohol — and in both, that very step takes away the most volatile part.

So the word absolute on a label tells you the product has been through alcohol, whether it came from hexane or from fat.

An absolute is thick, dark and much closer to the fresh flower than any other form. Jasmine absolute has a clear indolic note, while the distilled version has almost none. The reason is not that indole is destroyed by heat — it boils at around 254 degrees and still appears in some crude distillates. The reason is that esters are hydrolysed and the yield is so low that the proportions between groups of compounds are thrown off, so what leaves the condenser is a distorted version rather than a version missing one compound.

What you can check the moment you pick up the bottle is the texture. An absolute is thick and dark, and if wax remains it is cloudy or partly solidifies at room temperature — put a drop on a smelling strip and you will see it does not spread like an essential oil but stays as a streak.

On the label, look for the word absolute rather than accepting a blanket “essential oil”. If the label says essential oil but the contents are thick and dark, the two do not match — and the question worth asking is which solvent was used.

Solvent extraction was born in Grasse at the end of the nineteenth century, gradually replacing enfleurage with its enormous labour costs. For the first time in history it allowed the smell of flowers that cannot stand heat — jasmine, tuberose, orange blossom — to be captured at industrial scale.

That shift shaped the whole modern perfume industry. Most of the white-flower notes in the classic formulas of the twentieth century exist only thanks to this method.