It may be 40 degrees C outside and the whole of Australia is sweltering, but here in the perfumery it smells of cool, fresh rain on a flower garden. Very calming. It’s because I’ve been working on a conceptual fragrance that started off with the same accord as Aquarelle exploring the idea of the smell of water (see here http://evocativeperfumes.com/blog/?p=64). But whereas Aquarelle ended up moving in a bright, fruity direction with smells of ambergris and berries, this new fragrance (still to be named) has a more literal interpretation; that of the smell of rain – petrichor – a smell that universally proclaims the end of a dry spell, the life-giving relief of a downpour on dry soil, the release of signalling chemicals such as geosmin telling all living creatures with its powerful broadcast that there is water present. It’s a smell that I believe we have evolved to detect since the earliest days of life on this planet.
“Beets are deadly serious.” – Jitterbug Perfume by Tom Robbins
What is it about the smell of rain, particularly after a long dry spell, that is so emotive? In India the coming of the monsoon rains is so welcome that they have tried capturing the smell in an attar oil called Mitti Attar produced from the damp clay soil.
In 1964 two Australian researchers (Bear and Thomas) looked into what it is that creates the universally recognised smell and came up with the name “petrichor” (from the Greek words for stone and life blood of the gods) for the smell in their article in the scientific journal Nature. They thought that plants exude oils during dry periods which is absorbed by soil and by rocks. When rain comes along, it releases these oils along with a strong chemical called geosmin which combine to create the petrichor smell.
Now, geosmin by itself smells very strongly (do not try and smell it above a 0.1% dilution) of mold, soil, potato peels, damp and musty. To me it smells exactly like a rich, damp potting mix. That a single compound can smell so rich and complex by itself means that it must excite many different parts of the brain, hinting at its importance in our evolution.
A lot has been written about geosmin recently as researchers are realising just how important this volatile compound (along with other similar ones) is in nature. It is released by several types of bacteria and algae when they die, it’s in blue-green algae, in beetroot, in the 8000 worldwide species of liverworts and is sure to be discovered in many other places.
Humans are incredibly sensitive to geosmin – a million times more sensitive than we are to any other substance. We can detect it at a level of just ten parts in a trillion! So when a breeze carries a little in our direction we can immediately detect it and think ‘rain’s coming’. We can detect minute amounts in the taste and smell of bottom-feeding fish, so these fish are often eaten with lemon which disguises the geosmin – think blackened Cajun catfish or grilled catfish with lemon juice.
Camels can detect the smell of geosmin that had been released by bacteria in wet ground from 50 miles away and track the geosmin to find an oasis. It has been found that flies have neurons exclusively devoted to detecting geosmin and earthworms always head toward higher concentrations.
(The characteristic earthy flavour of beetroot is due to geosmin. It wasn’t known whether geosmin is produced by the beetroot itself, or whether it is produced by symbiotic soil microbes living in the plant. However researchers at Washington State University grew sterilized beetroot seeds aseptically and found geosmin in the seedlings, supporting the conclusion that beetroot is capable of endogenous synthesis of geosmin.)
Geosmin is harmless to life and its only purpose seems to be to signal the presence of life-giving water from one organism to another. My belief is that the first multicellular organisms evolved the ability to detect and head in the direction of higher concentrations of geosmin. If this is true, then it is the first chemical to be detected and acted apon – the first odour – ever. All life literally evolved around the ability to smell this and related compounds. Could it even be said that we evolved because of it? What a thought. No wonder we find petrichor so evocative!
So, back to my as yet unnamed perfume. As I said, it is based on the same accord as Aquarelle but also contains a little geosmin and smells completely different. I imagine that not many people would enjoy the idea of smelling of potting mix, so the geosmin is only dosed lightly – just enough to evoke the feeling of rain – and combined with fresh floral elements of gardenia and lily of the valley. Taking cues from the chef’s knowlege of how to serve catfish, I tried to use citrus notes to combine with the geosmin and provide the required freshness, however it really didn’t work. It may work in relation to taste, but seems not with smell. So no citrus here, folks. An Australian connection is present in the formula with the use of blue cypress oil grown and distilled in the Northern Territory to provide a woody bridge between the heart and base notes and then there is a wonderful vetiver used in the dry down along with some oakmoss.
Keep an eye on the Facebook page for news on this new fragrance, including what it’s to be called!