These oils are combined to make rose oil. The agitation associated with boiling prevents the rose petals from forming a compact mass that steam cannot penetrate. At Redbank, perforated trays covered with thinly spread rose flowers within the charge vessel have been used with direct steam distillation, and the problem of the flowers coagulating to prevent steam entry is avoided. Unfortunately, however, owing to the loss of phenyl-ethyl alcohol, a large proportion of which remains dissolved in the distillation water, the otto does not accurately represent the flower odour. Around 5t of flowers would be needed to produce one litre of rose otto.
Solvent distillation is now more frequently used to extract the aroma of rose blossoms.
The product of solvent extraction is a waxy, light brown, semi-solid material, known as a concrete. This material contains phenyl-ethyl alcohol in the same ratio as the blossoms. A typical solvent is hexane. Rose absolute is prepared from the concrete by extraction with alcohol. The absolute is a reddish liquid with a typical rose odour.