John Lanchester in The New Yorker:
So taste is mainly smell, and smell is a profound mystery. Why is it that one molecule
smells of spearmint, while its mirror image
smells of caraway? No one knows. When scientists create new molecules in the laboratory, they may know every detail of a molecule’s structure yet have no clue about what it will smell like. In 1991, scientists discovered the family of genes responsible for the nose’s roughly three hundred and fifty olfactory receptors; these, in combination, are what detect the presence of molecules and allow the brain to translate them into sensory experiences—so H2S, hydrogen sulfide, hits the receptors and our brain tells us that we are in the presence of rotten eggs.
A trained nose can become very, very good at isolating these sensory experiences and matching them with the relevant molecules. Theoretically, every known odorant molecule could have an agreed descriptor. The descriptor wouldn’t need to be in words: it could be a number, so that the wintergreen scent of methyl salicylate would be 172, say, and the garlicky odor of allicin would be 402. That would be the beginnings of a fully scientific language of taste—a joyless, inhuman prospect.
More here.