Being that it’s almost “crush” time, I find myself thinking about this a lot. To tell you the truth I think tannins play a much bigger role than just impacting a wine’s astringency. Will not argue the fact that some tannin molecules are much more astringent than others. But as far as color stability and enhancement I think the tannin/ anthocyanin ratio plays a big part in this or how we interpret or perceive the color of a given wine.
As far as enzyme go (maybe I’m just simplifying it way to much) they do not mysteriously create or produce more coloring pigment compounds. They only “work” with what color pigment compounds that are already present in the grapes. Enzymes act as a catalyst; they target certain reactants or substrates.
As far as Steve’s original question-The smell of Tannin. IMHO I don’t think that tannins themselves have a smell (Marl L as usually I think did a fine job in explaining this). Some tannin is based on acids. Could these tannins be fractionally broken down into their “acid” form? Could these acids in a fairly alcoholic solution form “aromatic” esters?