Humans are unable to distinguish individual properties of a smell.
There is no "blue", "sharp" or "sweet" in smell: encounter a new smell and the question will be "what does it smell like?" and not "how <smell adjective> is it?"; the answers given will invariably relate the scent to objects or experiences - "burnt toast", "old people", "fresh dog poop". Indeed, the words themselves probably conjure the respective smells almost immediately.

My thesis follows. This lack of is exactly why smells evoke memories the strongest of all senses.
Precisely because there are no abstract "blue" or "sharp" properties in smells that get lumped into a single category of "blue" or "sharp" is why we retain so much information from specific smells. We can't break down a smell into its component parts, so we must retain it in full.
Thus the random whiff walking past an alleyway takes you right back to that summer when you were 4 and your older cousin tried to feed you poop on toast at your grandparents' house.
It's almost paradoxical: our weakest sense, given time, becomes our strongest.