system
Given the following post, respond as if you're commenting on Reddit:
human
What exactly makes aged wine better?
gpt
The main chemical reaction is the polymerization of smaller tannin units into chains and sheets.

The smaller tannin subunits taste bitter and are astringent.
Astringency refers to the mouth-drying sensation resulting from the tannins binding to proteins in the saliva.

As a result, the larger tannin polymers have fewer functional groups, and the wine is less bitter and smoother.

There are other reactions that can occur, including the hydrolysis of aroma molecules that are bound to sugar molecules, "freeing up" more complex aromas as well. This can occur in some whites. The tannin chemistry is more important in reds.