Ask anyone to describe the smells they associate with summer, and they’re likely to focus on those connected with good weather – freshly mown grass, sea salt spray, maybe the smoke from a distant barbecue.
But one of the most complex and evocative aromas of the summer is also one that only occurs naturally after a spell of bad weather.
Petrichor is a blend of natural aromas kicked up from dry earth by summer rain. It’s that fresh, clean smell that hangs in the air just after the rain has stopped, and it has an instinctive mood-boosting effect for most of us.
Its name comes from ‘petra’, meaning ‘stone’, and ‘ichor’, the blood of the Greek gods. To get the full effect of this heavenly scent, the conditions have to be just right – so when is Petrichor most noticeable?
For Petrichor at its best, there’s a ‘goldilocks’ zone where the raindrops are heavy enough to disturb the surface of the parched earth, but not so heavy that they smother the natural aroma compounds they kick up.
When the rainfall is just right, the soil releases a mixture of plant oils and the earthy aroma Geosmin, a by-product of Actinobacteria in the soil.
If there’s thunder in the air, there may also be a hint of ozone, which is often said to smell like chlorine at high concentrations and like geraniums at low concentrations.
Together these smells add up to an earthy, green and clean scent with floral tones to it, as though the rain has freshly washed the land, and there are good reasons why we like it so much.
Petrichor leaves many people feeling revitalised, and it’s not surprising why – historically it would have been a sign of rain making the dry landscape more fertile during the hottest days of summer.
Some experts believe evolution has programmed us to feel more optimistic and appreciative when we smell Petrichor, which makes it a powerful scent to mimic in modern day fragrance products from perfumes to laundry detergents.
Early attempts to capture the aroma of Petrichor began in India, where it was absorbed into sandalwood oil and called ‘matti ka attar’, which translates as ‘perfume of the earth’.
Now we have a much better understanding of the science behind the aroma’s origins, and are able to produce a variety of similar fragrance ingredients and aromatic effects.
These range from aromas with a metallic, stormy edge, to softer, more floral and feminine variations like Arran Aromatics’ ‘After the Rain’, which blends precious woods with rose petals, floral citrus and musk.
If stormclouds could dream, Petrichor is what their dreams would smell like. It’s one of the most evocative aromas of late summer and early autumn – and one to which evolution has programmed within us a positive response.