Chemical contents

Bulgarian rose oil is a yellowy-green liquid with the following physical and chemical properties for quality testing: d 0.848-0.861, nD 1.4530 – 1.4640, solidifying at approx. 16.5-23.5°C, acid value 0.92 – 3.75, ester number 7.2 – 17.1, saponification number 8.0- 21.0 . The principal contents are 34 – 55% (-)-citronellol, 30 – 40% geraniol and nerol, and there are additionally small traces of linalool, farnesol, citral, 2-phenylethanol, carvone, rhodinol, and nonyl aldehyde. Altogether, natural rose oil contains approximately 230 types of molecule. Bulgarian rose oil contains traces of the compounds damescenone and rose oxide, which give Bulgarian rose oil its distinctive character. The principal chemical component of the rose flower is 2-phenylethanol. Due to its good solubility in water, 2-phenylethanol passes almost completely into the aqueous phase during steam distillation. Consequently rose water contains a high quantity of 2-phenylethanol.

The petals contain well below one per cent of ethereal oil. On account of its volatility, the rose oil content reduces steadily in the course of the flowering season; rose flowers for distillation must therefore be gathered by hand every day, and only from the first crack of dawn until sunrise at the latest.

The components of rose oil that determine its character are the acyclical monoterpene alcohols geraniol (up to 75%), citronellol (20%) and nerol (20%); in addition to these, long-chain hydrocarbons like nonadecane and heneicosane have been found.

A very significant trace component is β-damascenone: despite its low concentration (0.01%), this C13-norisoprenoid has a noticeable influence on the quality of the rose oil. Together with the structurally related compounds β-damascone and β-ionone it is formed from the breakdown of the plant's own carotenoids; the dominant scent materials of saffron and pandanus leaves arise in the same way.

Also important for the scent of roses is 2-phenylethanol, which, however, is lost in steam distillation whereas it becomes enriched in the rose water. This is why the scent of rose oil is not quite identical with that of rose water.

Even under the most favourable growing conditions it takes 100kg  of rose petals to yield just 10g  of oil (0.01%); this amount can, however, be tripled by re-distillation of the rose water that is produced.

Alternatively it is also possible to use solvents, typically hexane, for extraction, resulting in a semi-solid greenish mass. Yields from this process are ten times higher than from distillation; moreover, the natural content of 2-phenylethanol is preserved (approx. 60% of the volatile fraction).