Reference point
Crush a sprig of fresh coriander, leaves and stalk together.
Do this before you read on. An entry only works when you have just smelled the thing.
Green, pungent, fresh, and very quick to evaporate. For some people it gives a clear impression of soap.
Many entries in this dictionary divide readers — durian, fermented shrimp paste, the milkwood flower. But this is the only entry where that division has an identified genetic cause. A gene variant linked to an olfactory receptor makes about one in ten people perceive the aldehydes in coriander as soap. Two people smell the same sprig and genuinely receive two different signals.
Leaf and seed are two completely different smells. Roasted coriander seed is sweet and warm and belongs to the spicy family; the leaf is green and pungent and belongs to the green family.
How to smell it
Crush a sprig of coriander and smell it. Ask a few people around you to smell and describe it too. If someone in the group says soap, you have just observed a genetic difference in smell first-hand.
Why this one is hard
It is not hard to recognise, but hard to describe objectively, because the experience genuinely differs from one person to the next.
Don’t confuse with
This entry
Coriander leaf
Green family
The same group of aldehydes, but culantro is many times stronger and has a damp layer that coriander lacks.
This entry
Coriander leaf
Green family
Seed and leaf of the same plant, in two different scent families. The seed is sweet, with an orange note; the leaf is green and pungent.
Scientific note
About one in ten people carry a variant of the OR6A2 gene that makes them perceive the aldehydes in coriander as soap. It is one of very few cases in which a difference in smell between people has been traced to a specific gene. Two people smelling the same sprig genuinely receive two different signals, and neither of them is wrong.
Decanal boils at around 208 degrees, so it is not a light compound. Coriander still belongs to the top stage because long-chain aldehydes have very low detection thresholds — you notice them at concentrations at which most other compounds are still invisible.
In Vietnamese life
Fresh coriander is scattered over most soups and stir-fries in Vietnam. It is also part of the pot of mùi già water for bathing on the last afternoon of the lunar year in the north, using the whole plant once it has flowered and set seed.