To yield an absolute, the aromatic plant material (flowers, leaves, etc.) is extracted by hydrocarbon solvents such as benzene or hexane. The plant material is covered with the solvent and slowly heated to dissolve the aromatic molecules. The solvent extracts the odour and then the solvent is filtered off to produce a ‘concrete’. A concrete is a solid, wax-like substance containing about 50 per cent wax and 50 per cent volatile oil such as jasmine. To obtain the absolute the concrete is mixed with pure alcohol to dissolve out the aromatic molecules, and then chilled. This mixture is filtered to eliminate waste products and to separate out insoluble waxes. The alcohol is evaporated off gently under vacuum. The thick, viscous, coloured liquid known as the absolute is left behind.