Most expensive fragrance: the elusive scent of the Florentine iris

In the early days of perfumery, when all ingredients had to be extracted from natural sources, the choicest and most prized odours were the most costly ones to produce: violet, jasmine, Damascus rose, lily of the valley. Thanks to painstaking work by chemists and perfumers, all of these fragrances can now be reconstituted from industrially synthesized chemicals and are used in large quantities not only in expensive perfumes but in everyday cosmetics such as soaps and creams.

The most expensive ingredients in 21st century perfumery

Yet a once cheap substitute for the priceless violet extract continues to defy the ingenuity of fragrance chemists and has in consequence become one of the most expensive ingredients in 21st century perfumery: Orris root oil, which is prepared from the dried rhizomes of the Dalmatian or Florentine iris (Iris pallida) and can cost up to $75,000 per kilogram.

Notoriously difficult to synthesize

Orris root oil is a mixture of five different closely related terpene derivatives, (+)-cis-𝛼-irone, (−)-trans-𝛼-irone, (+)-𝛽-irone, (+)-cis-𝛾-irone, and (+)-trans-𝛾-irone that share the same basic carbon skeleton but differ in their stereochemistry and in the placement of a single double bond. They are notoriously difficult to synthesize and can usually only be obtained as racemic mixtures, i. e. impure preparations that contain both members of a pair of stereoisomers. Due to the difficulty in obtaining pure orris oil ingredients, fragrance chemists have not yet been able to reconstitute this unique scent from its individual chemical components, nor from less costly ingredients, as has been possible with almost all other floral fragrances.

Orris root – the “secret ingredient”

To this day, orris root remains a sought-after “secret ingredient” for perfumers, the scent of which is dependent on the particular harvest year of the iris flowers from which it was obtained. It comes as no surprise then that orris oil is used in some of the most expensive creations by the luxury perfume brands Chanel, Hermès, Guerlain, Dior, Calvin Klein, and others.

From: Scent and Chemistry: The Molecular World of Odors, 2nd Edition, Günther Ohloff, Wilhelm Pickenhagen, Philip Kraft, Fanny Grau, ISBN: 978-3-527-82998-9