Concrete

Flowers are spread in layers on trays inside an extractor and washed with solvent several times. The solvent dissolves aroma molecules and the oil-soluble matter on the petal surface. The extract passes to an evaporator, where the solvent is distilled off and recovered for reuse. The last traces are removed under vacuum so the temperature stays low.

Flowers must reach the factory soon after picking, since many white flowers keep changing their scent once cut. In Grasse they arrive within a few hours. The first volatile solvent extraction plant in Grasse was built by the Chiris firm in 1898 and opened in 1899. The French Ministry of Culture heritage record lists the solvents handled there as petroleum ether, benzene, alcohols and acetones.

Today hexane is the usual solvent for fresh flowers. Benzene is no longer used: IFRA has prohibited it as a fragrance ingredient since 1988 and caps any residue at 1 ppm in the fragrance mixture.

A concrete has two parts. The aromatic part is volatile and semi-volatile molecules, for example benzyl acetate, linalool and indole in jasmine. The non-aromatic part is plant wax, long-chain hydrocarbons, fatty acids and pigments.

Because it keeps its waxes, a concrete does not fully dissolve in ethanol and is of little use in alcoholic perfume. It dissolves better in oils and fats, which suits soap, waxes and solid products. Its scent is usually rounder and slower than the absolute of the same flower.

Concrete yields are low and vary with cultivar, season and picking time. A study published in 2012 obtained 0.35% concrete from fresh jasmine grandiflorum flowers extracted with n-pentane. For tuberose, a 1996 study of four cultivars measured about 0.13% in single-flowered types and about 0.11% in double types, with October flowers yielding more than March flowers.

For Turkish Damask rose, published concrete yields are likewise well under one percent of flower weight. Going from concrete to absolute loses more: for rose, a 2003 study recovered 58 to 64% absolute from the concrete.

These figures come from specific studies, not industry standards. Factory yields may differ.

In trade, the product from orris rhizomes is often called "orris concrete" or "beurre d'iris". The name comes from its look: it sets into a cream-coloured waxy mass at room temperature. Yet it is made by steam distilling the dried rhizomes, not by solvent extraction. ISO 9235:2021 itself uses "iris butter" as its example of a steam-distilled essential oil.

The texture comes from fatty acids, mostly myristic acid, carried over with the steam. The main odorants are irones such as alpha-irone. On an orris label, the word "concrete" describes the physical form, not the method.

A complete label gives the Latin species name, plant part, country of origin and extraction solvent. If the solvent is not stated, the supplier can be asked; hexane is the common answer. Concretes are usually sold by the kilogram as a block or paste and need gentle warming to dispense.

The word "concrete" attached to dried flowers, roots, resins or moss deserves a second look. Under ISO 9235 an extract of dry material is a resinoid; concrete is reserved for fresh material. Trade names do not always follow this. EU cosmetic allergen labelling is calculated from the concrete's actual composition, as with essential oils.