Monday, September 17, 2012

The Smell of the Earth After the Rain: Geosmin, Petrichor & Other Wonders

The first heavy drops of rain fell on the thirsty ground yesterday after a hot, hot summer that scorched our conscience. It seemed like release, like tears falling after a gigantic pressure mounting inside that had overflown, ready to burst.
"With the first drop of rain the summer was killed. Soaked were the words which starlight had born. Words that were meant just for you." writes Odysseas Elytis. 
This sweet melancholy of autumn is inextricably tied to the pit pat of the raindrops on the window pane, much as it sounds corny. Like many, I adore the ambience after the rain; when everything seems washed, purged, the green leaves and flowers shiny fresh with droplets hanging onto them refracted into myriads of rainbows in the emerging light; with the distinct smell of the earth that has soaked the water and brought out a scent at once musty and refreshing, a scent that is ancient and at the same time of the moment, galvanizing, a scent of the divine and the pagan. But what makes that delicious scent, popular enough to be first unapologetically encapsulated into a fragrance to sell by Christopher Brosius in his Fragrance Library for Demeter by the eerie name "Dirt"? The answer is more enjoyably lyrical.

Petrichor is the name of the scent of rain on dry earth, which aided by the compound geosmin contributes to that delectable ambience of upturned earth and musty deliciousness which walkers of the woods have been known to enjoy with all their might. Due to poetic justice, I suppose, and because everything is paid upon at the cashier eventually in this world, both words have a Greek origin: "Petrichor" literally means the fluid in the veins of the gods hitting stone (from the words πέτρα i.e. stone and ιχώρ i.e. the mythical lifeblood of the Gods). "Geosmin" is simpler, more to the point: from the Greek word for earth, γαία (deriv. γεο-) and οσμήν i.e. smell; simply put, "the smell of the earth". The term "petrichor" was coined in 1964 by two Australian researchers, Bear and Thomas, for an article in the scientific journal Nature. In their article, it is argued that certain plants exude an oil during dry periods which is then absorbed by clay-based soils and by rock. The hitting of the ground during the rain releases this oil alongside geosmin, a germacranoid sesquiterpene or a trans-1,10-dimethyl-trans-9-decalol for the more chemically minded ~or simply a by-product of microorganisms, which acts as a metabolite.

Geosmin is produced by a number of microorganisms amongst which the mycelial soil bacteria Streptomyces. Geosmin is exactly that distinct smell that soil gives off when disturbed or just rained upon and its human detection threshold is so low (allowing almost all to savor it) and so pleasant, it is used to confer an earthy scent to perfumes! But careful: in flavor, by contrast, geosmin can turn a glass of water or wine (or fruits or vegetables) musty and unpleasant for consumption. Even lightning contributes to the scent of the earth after the rain nevertheless; the presence of ozone is electrifying, producing that energetic, come what may, putting on boots and clutching a cane walk in the woods mood one doesn't know they had in them until it actually happens. This is the magic turn of the screw that makes fragrances such as Creed's classic Green Irish Tweed (with the infinitely matching name to this fervent desire) and the quirky enchanted forest of Ormonde Woman work so well.

Several perfumers try to recreate that complex smell of the forest floor; upturned, a little decayed, yet at the same time fresh, cooling, a sort of clean all the same. Great vetiver fragrances, such as Guerlain's classic Vetiver and Vetiver pour Elle, Route du Vetiver by Maitre Parfumeur et Gantier , Chanel's Sycomore, Lalique Encre Noire or F.Malle's Vetiver Extraordinaire mingle that particular freshness that the exotic grass root of vetiver possesses alongside a smokier, mustier background which brings on a crepuscular tinge. Some patchouli fragrances, notably Voleur de Roses by L'Artisan Parfumeur utilize the more wine-like facets of the rose and the Indian leaf material to render a scent that approximates well a garden after the rain. Herbal accents and iris notes alongside grassy-musty ingredients (such as vetiver, angelica, wormwood or oakmoss) also produce this effect as in Roadster by Cartier, L'Artisan Parfumeur Timbuktu, the stupendous Derby by Guerlain, Angeliques sous la Pluie (F.Malleand Dior Homme.

It's interesting to note that geosmin doesn't just contribute to the smelly landscape but could be a way of promoting sporulation as it occurs where humidity is involved. "Camels may well smell out an oasis by sniffing the air for traces of the fragrant metabolite. While camels quench their thirst, hordes of Streptomyces spores will be supped with the water or will find a way to stick onto the animals’ hides. In this way, spores can be carried for miles. In the same way, some cacti flowers may also use the geosmin scent to fool insects, in a sort of fragrant mimicry. Indeed, insects are attracted to the plants in the hope of a little refreshment, and in their quest for water, they actually serve as pollinators!"[source]

As with everything involving smell, there's more than meets the nose...

Music clip "With the First Drop of the Rain", lyrics by Greek nobelist poet Odysseas Elytis, set to music by Manos Hadjidakis and sung by Dimitris Psarianos.


  1. Tamara.*J.22:26

    Loved, loved reading this.
    I run in a forest all year long here in Washington and I am mad for the smells of it.
    I drink it in and feel alive.
    Nothing beats it....besides my beloved's hair when we cozy up at night after a long day..


  2. Anonymous22:40

    What a wonderful blog post! It was so interesting to learn about the chemistry behind the smell of petrichor.

    As an aside, here's a pop culture note: in episode 12 of Series 6 of "Dr. Who," there is a department store selling a perfume called Petrichor. Outside of perfume blogs and message boards, this is the only place I've ever seen the word used. Kudos to the writers of "Dr. Who" for expanding the vocabulary of their audience.

  3. T,

    very happy you did enjoy this so much! Thanks for letting me know :-)

    You're infinitely lucky....ah, to run amidst the trees and the air of the forest. Cherish it! I completely understand what you're saying and wish I could do the same, city kid that I am.

  4. A,

    thanks for the kind words!
    It is an interesting subject, isn't it?

    Dr.Who. Cult series. For more than one reason, now you mention this (unknown to me) fact! Yeah for the producers and writers! And a great reference for us perfume lovers. :-)

  5. Thanks so much for this; and yes, as another Dr. Who fan, I was super happy to see this word used as a perfume!

  6. Stephan07:40

    Here you are at your best again. I enjoyed the reading immensely, your way how to evoke the mysticism and not shying away from chemistry talk. And in the end the lyrical feel is left intact, despite the scientific explanations. I love your articles because they are all encompassing.

  7. Carol,

    glad it was pleasurable to read and wow, Dr.Who has a lot of perfumephile fans! :-D

  8. Stephan,

    aww, blushing from your lovely compliment.
    I'm glad I can share what makes the world "tick" for me. It's wonderful to find kindred spirits in the process :-)

  9. brie12:10

    Laurie Erickson's Forest Walk came to mind while reading this fantastic article! As always, thanks for the education and insight :)

  10. Marvellous post!
    One of the most evocative and deeply emotive realms of perfumery.
    May I just add the often overlooked and very interesting "The Smell Of Weather Turning" from Lush's Gorilla range. I may be wrong here but I think it actually contains geosmin. While the range seems pitched at the lower end of the market, this seems to free them to experiment and pursue some often quite radical ideas.

  11. Great piece Elena. Today's article is one of the most interesting and informative I've read and regarding scents I truly love (can't say the same about Autumn though which is my least favorite season). The great song of Xatzidakis feels like a natural choice

  12. Fascinating article! I love how Bertrand Duchafour creates an Winter earth like smell in Sienne L'Hiver(I think he uses pyrazines?) I also love the use of Angelica in perfumes to impart an earthy herbal note my favorite being Amouage Lyric Man.This was a great educational article on and eclectic topic.Keep them coming! :)

  13. Brie,

    good thinking: haven't tried that one yet!
    Thanks for the kind words. :-)

  14. Paul,

    thanks for chiming in, your kind words and your contribution to this subject. It very well could be. I think most recreate this ambience but it would be facinating to see how a company that uses a lot of natural and interesting materials such as Lush would go about this.

  15. K,

    thank you! :-)
    It seemed like such a natural fit for an autumnal mood which these days provoked in me that lying around in preparation since last winter seemed like a LOOOOOOOONG time and I decided to upload with an appropriate introduction.
    Yeah, Hadjidakis finishes the whole thing off, doesn't he? :-)

  16. RVB,

    thank you :-)

    I love the uniqueness of Sienne l'Hiver. I think it depends a lot on the dusty pruned olives and stone-road olfactory elements, though need to check again about the pyrazines (I think they're absent, but not 100% sure).
    Angelica is an overlooked ingredient, though I can see how it is a little unpopular with modern audiences fed on vanilla and fruits.

  17. The description reminds me of that of Mitti Attar, where actual cakes of rain-soaked earth/dirt is co-distilled with sandalwood oil.

    1. Yep, mitti attar does remind you of rain soaked earth. I know coz I have it ☺️

  18. Melissa,

    oh yeah, very good observation!! I have heard of this but haven't had the chance of trying for myself from what I recall. Sounds heavenly though.

  19. I thoroughly enjoyed this article. The word, petrichor, in the title drew me in, Dr. Who fan and perfumista that I am. Petrichor -- for the girl who's tired of waiting.

  20. Anonymous11:14


    Nice article...

    When I googled, found that according to Sigma Aldrich, for 10 mg of racemic (±)-Geosmin price is 769USD.. Couldn't find anywhere about (-)Geosmin which is natural.. Is there a high requirement for Geosmin around the world? Or is this cost high???


  21. Anonymous21:19

    I live in Broken Arrow, Oklahoma, and when the first drops of rain hit the parched earth, I smell a sweet scent unlike anywhere else, and I have lived, as a military wife in many places from coast to coast, border to border and in Europe. I hope you may experience it, too! Come and sniff!


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