I've noticed with several wines that after a glass is poured the wine may go down very nicely, but after the glass has sat still for a few minutes the next sip will start as well as before, but will have developed a strong after-bite at the back and center of the tongue where it meets the throat.
If, however, the wine is swirled gently in the glass a round or two before the next sip the after-bite is greatly deminished.
Not tannins and not carbonation. I don't think it's acid.
What is it? Esters?
Since beginning to try wine making I've also begun to pay a lot more attention to what might be the actual components of the whole making up wine. This one has me stumped. Glad to have discovered a simple swirl can make such a nice effect.