Asparagus and its after effects – the answers.

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Being English I have impeccable manners, of course. I am a bit like Joanna Lumley. (Unless I am cross then it’s more like Ray Winstone). Therefore I would never dream of alluding to bodily functions at the dining table when serving asparagus. I shudder at the less self contained contestants on UK TV’s Come Dine With Me announcing, as their hostess serves the finest asparagus-based dishes with black truffle and quails’ eggs, “Eeeeee, this’ll make us pee stink in’t morning.”

Actually, research has shown 1 that 8% of us can detect no odour and another 8% can produce no odour. A fortunate 3% can neither detect nor produce and therefore make ideal flatmates/life partners.


Most likely not in the odour free 8%.
Most likely not in the odour free 8%.


[divider]What are the key flavour chemicals that make it through the renal system and why are they so volatile? [/divider]

The stalks of the Asparagus officinalis plant have photosynthetic branches rather than leaves. The tips are immature buds and under their cultivated mound of soil are far-reaching rhizomes similar to the ginger plant.

The spears must be harvested when young as once cut they use up their sugar reserves rapidly and grow tough and fibrous. Any asparagus eater will know that tender and smooth is best.

The smell is to do with the way humans metabolise sulfuric compounds and the way sulfuric compounds are the pre-cursors to thiol chemical compounds.

Aspargusic acid, C4H6O2S2 has a di-sulfide functional group. There it is, on the bottom, see its two sulfurs?




Its function in the asparagus plant is to ward off attacks from parasitic round-worms (yes, these things are out there in the soil). During their time in the human digestive system as they knock about with all those enzymes the thiols get loose and thiols are volatile which means, of course, that they are powerfully smelly. The particular thiols that work their way out in Asparagus are2

  • methanethiol, CH3SH, which is also found in skunk spray.
  • S-methyl-3-(methylthio)thioproprionate
  • and S-methyl-thioacrylate.



Members of the Psychology department of the University of Southern Florida had their work cut out in 2009 while producing their paper “Excretion and Perception of a Characteristic Odor in Urine after Asparagus Ingestion: a Psychophysical and Genetic Study1.” One can only imagine the bribes and begging done to gather enough people for the sensory perception panel. In fact, while only 38 people participated in the test, the paper reports that

“some people could not complete the smelling phase because of unanticipated aversions to urine or lack of availability to complete testing.”

I’d be kind of busy on that day, too.


Study participation recruitment is not always easy.
Study participation recruitment is not always easy.


Anyway, the while the metabolic reason behind the inability produce the odour is unknown the inability to smell the odour is associated with a single nucleotide polymorphism (rs4481887) within a 50-gene cluster of olfactory receptors.

Which type of person are you? How are your nasal gene-clusters? And yes, I am expecting some comments.




[divider]Cooking with Asparagus [/divider]


Personally, I prefer to serve it as whole spears.

  • steamed, blanched and dressed with best butter or olive oil flavoured with truffles or a richly perfumed extra virgin (imagine that said in the voice of Brian Sewell). I add some good bacon or pancetta on the side,  some fresh parmesan and of course lots of black pepper on top. I am told a barely poached egg goes down a treat too.


When I was cooking for a living I knocked up this salad for Patti Smith (KLANG – name-drop), while she was recording Gung Ho in Crouch End with producer Gil Norton.

  • Poach Salmon fillets poached a bit of lemon juice, let them cool and dress them with a dill and Dijon mustard vinaigrette using garlic infused white wine vinegar. Poach and blanch fine asparagus spears in fresh water and place on the serving plate. Dress with finely sliced radishes and spring onions, and a few big green kalamata olives and a squeeze of juice from a fresh orange. Arrange the dressed salmon on top and add some sea salt and black pepper. Serve at room temperature.  Ms Smith, I have recorded in my notebooks (this was 1999, no such things as instagram and tablets), commented “Excellent. I challenge any restaurant in Manhattan to make an appetiser as good as that.” Which was nice.
patti by rm
Patti Smith photographed by Robert Maplethorpe


1. Pelchat, M.L., Bykowski, C., Duke, F.F. and Reed, D.R. ” Excretion and Perception of a Characteristic Odor in Urine after AsparagusIngestion: a Psychophysical and Genetic Study”. Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA 19104-3308, USA and Department of Psychology, University of South Florida, 4202 East Fowler Avenue, Tampa,FL 33620-7200, USA. Published in Chem. Senses 36: 9–17, 2011 doi:10.1093/chemse/bjq081

2. Tom Coultate from his marvelous book, Food and the Chemistry of its Components, RSC Publishing. p305.






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