Put two spoonfuls of sugar in a dry pan, heat it over a medium flame, and stand there smelling continuously until the sugar smokes.
Write one word at each stage: when the sugar melts, when it turns golden, when it reaches a deep brown, when it starts to smoke.
Those four words will be completely different. And you will have witnessed something no article can convey for you.
One thing, four smells
Sugar at room temperature is almost odourless. Heat it and caramelisation begins, producing furaneol and a group of burnt-sweet compounds. Keep heating and smaller molecules go on breaking down and recombining, giving smoky and bitter compounds.
At some point the smell has left the gourmand family for the smoky and mineral family. You can hear the line being crossed.
Very few smells let you watch a change of family happen right in front of you in half a minute.
Why Vietnamese braised dishes are hard
The line between good caramel sauce and burnt caramel sauce is so narrow it is measured in seconds. The cook judges by nose rather than by clock, because the clock does not know whether the pan is thick or thin, the flame high or low, the sugar damp or dry.
It is a body of sensory knowledge at work every day in millions of kitchens, and almost none of it has been written down.
The same principle, three more exercises
Fried shallots: smell when the shallots first go in, when they turn golden, when they go brown. Three smells in one pan.
Fermented sticky rice: smell it once a day for five days. It is the longest exercise in the dictionary, and it shows you a smell changing by the day rather than by the second.
Pickled mustard greens: freshly soured, fully soured, over-fermented. Three stages, three smells, and cooks tell them apart to decide which dish each goes into.
This changes how you smell everything
After the sugar-pan exercise it is hard to go back to asking what does this smell of. The better question is where is this in its process.
A perfectly ripe jackfruit and an overripe one are two smells. A freshly opened bottle of essential oil and the same bottle a year later are two smells. A drop on a smelling strip at minute three and at hour four are two smells.
This is also the foundation of the idea of notes, and the reason an analysis should be read in order of boiling point rather than in order of share.