Reference point
Lightly crushed fresh leaves of Vietnamese coriander.
Do this before you read on. An entry only works when you have just smelled the thing.
Green, but with a strange fatty note unlike any other herb — close to old orange peel mixed with soap.
That fatty note comes from straight-chain aldehydes, the same group that builds the smell of orange peel and appears in many classic perfumes of the twentieth century. It is one of the most unexpected bridges in this dictionary: a herb eaten with fertilised duck eggs and a bottle of French perfume sharing one family of molecules.
Vietnamese coriander has no sweetness at all. If you notice sweetness, you are almost certainly smelling the basil or Vietnamese balm lying next to it on the plate.
How to smell it
Crush two or three leaves and smell at once. Concentrate on finding the fatty part behind the green — it sits at the back and takes a few seconds to appear. If it is hard to catch, smell it alongside a piece of orange peel left out in the air for a few hours; what the two have in common is what you are looking for.
Why this one is hard
The word fatty does not sound right for a herb, so beginners do not think of it and therefore do not look for it. Once you have caught it, you will never smell Vietnamese coriander the same way again.
Don’t confuse with
This entry
Vietnamese coriander
Green family
Perilla is round and warm; Vietnamese coriander is edged and has a fatty note from straight-chain aldehydes.
Scientific note
Vietnamese coriander is rich in straight-chain aldehydes, mainly ten-carbon decanal together with twelve-carbon dodecanal.
Coriander and culantro contain this group of aldehydes too — the three herbs overlap considerably in composition. The difference is not that one has longer chains than another but lies in the ratio between the aldehydes and in the presence of unsaturated forms. Vietnamese coriander leans further towards dodecanal than coriander does, which is part of why it stays longer on the hand and in the soup bowl.
In Vietnamese life
Vietnamese coriander is a herb characteristic of Southeast Asian cooking.