Opinions are quite varied on whether adding fresh coriander (aka cilantro) to a recipe makes or breaks the dish. Some folks simply love the stuff while others find the herb quite repulsive - often noting a metallic, soapy or otherwise unpleasant flavor (other descriptions of the repulsive taste and/or smell can be found here) a description that seems quite different from how fans describe it. So why the disparity??
Thanks to work by a few diligent and inquisitive scientists, we do know a few things about this love-hate relationship with one of my favorite herbs. Some these discoveries have been stumbled upon while working on more important issues while others come more focused and direct studies of the plant.
Coriander (aka cilantro or Chinese parsely) is the common name of the plant Coriandrum sativum, a member of the carrot family Apiaceae or Umbelliferae. The young leaves are the herb called cilantro, while the older leaves and seeds are called coriander - although the herb is commonly referred to by both names. For some interesting Coriandrum chemistry, check out the chapter on the chemical properties of the herb starting on page 190 of Chemistry of Spices, available through Google Book Search. Unfortunately the book doesn't have much info on why some find the herb so revolting...
So why the divide? According to work by folks like Charles Wysocki from the Monell Chemical Senses Center it seems there are very likely some genetic factors that contribute to the preference. This based on preliminary work comparing pairs of twins with non-twins - if its heritable, pairs of identical twins will share a preference more so than fraternal twins, with the lowest proportion of shared preferences seen between non-twin siblings.
Initially some believed the cilantrophiles among us were unable to taste or smell some particularly offensive chemical found in the plant. This is a reasonable hypothesis, and is in line with similar phenomena such as the more common example involving asparagus (although I recently learned that producing and being able to smell the offending byproduct in this case are two separate issues).
With cilantro, it turns out this notion is a bit off. There does seem to be a difference in smelling (and tasting) ability among the cilantro lovers and haters among us, but according to this essay by Josh Kurz on the NPR website, the smell some folks are missing out on is not a foul one, but that pungent lemony smell so adored by cilantro lovers. If you are among those who hate cilantro, you really might not know what you're missing!
Given the descriptions I have heard and read, there may indeed be some other more unpleasant smells that are only detectable by the unfortunate few. This could simply be because the compounds that smell so good to some are themselves the culprits, being pleasant to some and repulsive to others. The GC anecdote in Josh Kurz's article suggests otherwise, however. So the two smells/tastes are indeed caused by two different chemicals. Unfortunately the essay doesn't mention whether or not researchers Wysocki and Preti were also able to smell the unpleasant compounds.
Interestingly, this information doesn't show up on ihatecilantro.com!
So will the world be a better place for knowing all this? Probably not, but I can already imagine someone slaving away for Monsanto trying to get rid of the repulsive compounds - after all, there is a big difference between "tastes bad" and "tasteless"!