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Benjamin Franklin in a 1781 letter to the royal academy, “A few stems of asparagus eaten, shall give our urine a disagreeable Odour.”
Marcel Proust: “Transforms my chamber pot into a flask of perfume.”
Donald Trump: Bottle it and sell to the Mexicans as “Trump Body Spray.”
During digestion our bodies convert asparagusic acid into sulphur containing compounds (Dimethyl sulfide, Dimethyl sulfoxide, etc.). These sulphur containing molecules are also found in garlic and skunk spray.
So why does the solid vegetable smell innocuous while our asparagus pee smacks the nostrils? Asparagusic acid is not volatile, (it has a high boiling point) while those sulphur containing molecules which are produced through digestion are volatile (very low boiling point) so they vaporize once they hit the air.
But have you ever been discussing this phenomena when somebody claims never to have smelled it? I’ve often written these people off as either unobservant or secretly aliens, but turns out that there’s a segment of the population who can’t decipher the smell (around 30%). Scientists believe there is a olfactory gene which allows most of us to smell this vegetable in our urine. In 2010 a genetic sequencing company asked 10,000 customers if they could smell asparagus, and found those who couldn’t shared a single genetic mutation, a switched base pair amongst a cluster of 50 different genes that code for olfactory receptors. Hmm. So what else am I smelling that other people don’t smell? I digress.