The Smell of Rain

Some people wait for Godot, others wait for Guffman. Some wait for a star to fall, or for the world to change – and others wait for Lefty.

It’s my birthday today – and like most people born in September, I wait for Petrichor, a noun that almost deserves to be in upper case, since it is such a wonderful thing.

Purists will tell you that Petrichor is really only ‘the blood of the gods’ (ichor) with the prefix petri (stone) – but when you live in Malta, where the rain that breaks the summer drought over limestone, the word acquires its special distinction.

In any case, ichor (“tenuous essence”) is not blood, but an ethereal, transparently golden fluid that was supposed to run in the veins of Greeks gods – a component of ambrosia and nectar too, if you please, and poisonous to mortals.

Of course, it’s not only Greek gods that do not have blood as we know it in their veins.

Some arthropods – including spiders, crustaceans such as crabs and shrimp, and even some insects such as stoneflies – have haemolymph in their circulatory systems instead of both the blood and interstitial fluid of vertebrates. Some non-arthropods such as mollusks also possess a hemolymphatic circulatory system.

Poets since Victorian times have used it to mean a divine drink – or mundane wine. In a complete circle, oenologists have lately begun using the word petrichor to describe a characteristic nuance of wine, when they want to evoke the scent of rain drizzling over rocks, as I am told is extant in Grüner Veltliner, Alsatian Rieslings, Argentine Malbecs and Loire Valley reds. The smell of rain calls to mind different things to different people. In me, it stirs up memories of funerals of people I have loved – somehow, a rainy afternoon makes a goodbye bleaker than it otherwise would be…. especially when it’s out-of-season rain, as if the elements want to unite with one in sorrow.

The “earthly” meaning (both senses) of the word petrichor was used in the March 7, 1964issue of the Journal Nature by two Australian geologists I.J. Bear and R.G. Thomas. Their article was entitled The Nature of Argillaceous (“consisting of or containing clay”) Odour in Nature. They explained the process of how the smell that reminds us of childhood days of splashing in grandparents’ internal yards obtains. Oil exuded by certain plants during dry periods is adsorbed by rocks and soils. When it rains, the stored molecular oil is released into the air (along with geosmin, “ earth-smell” another compound) to produce the characteristic after-rain smell. Geosmin gives beets their “earthy” smell; the human nose is able to detect it at concentrations as low as 5 parts per trillion.

It is the geosmin, not the petrichor, which is produced by microbes; it is released when they die. This is why, when the water supply of an area comes from surface water and not from artesian wells or reverse osmosis plants, the water may taste unpleasant. This typical “muddy” taste is also present in freshwater fish that thrive in warm, slow-moving, and muddy rivers, or those that live in the bottoms of lakes – carp and catfish being two examples – and tends to be stronger in warmer months.
However, if the water is acidic, geosmin will decompose into odorless substances. This is the same reason that vinegar and other acidic ingredients in fish recipes help reduce the “earthy and mossy” flavour of strong-tasting fish (including sea-fish that eat kelp, which is high in iodine and imparts a metallic taste to the flesh).

In a follow-up paper, Bear and Thomas had demonstrated that the yellowish oil, composed of more than fifty distinct chemical substances, serves the purpose of retarding the germination of seeds and early plant growth, since they would have died had the drought continued. Indeed, some Australian publications indicate that the omnipresent eucalyptus trees also release revivifying petrichor. When it is washed into the waterways, creatures know that the season is sufficiently wet to support breeding.

Ammon Shea’s claim to fame is that he read through the whole of the Oxford English Dictionary – and published a book about it. He says that petrichor is one of his favourite words.

There is, of course, a whole slew of hyetal (“related to rain”) words that are in some way related to rain – drizzle, hail, deluge, downpour, showers- but none is as mellifluous and redolent of memories as petrichor.small text size

 

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