I've been drinking whiskey for 14 years, and whisky for 10, but didn't really get into it until 2008 or so. It took a lot of tastings and reading before I could describe what I tasted. I'm still not great at it.
I actually went out and bought a bunch of spices and foods to practice detecting certain notes.
Understand, you may not actually taste/smell "butterscotch", but instead smell/taste something that REMINDS you of butterscotch.
Part of it is just thought/emotion evoking prose.