system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:What exactly happens over time to alcoholic beverages that get better with age?

Bonus: Why haven't we figured out how to accelerate the process?
gpt
Most of the time the aging is done in certain kinds of wood (notably oak) which adds new flavor compounds, absorbs some undesirable flavor compounds.  Wines tend to age in the bottle are those high in tannins which are bitter compounds (unripe persimmons are a great example) that combine to create new and interesting flavors over time.

Speeding up oak aging only requires more surface area to liquid which can be done but is more expensive (small barrels) or not traditional (tanks with oak chips).  Aging in the bottle can be speed with increases in temperature but that increases undesirable changes at a higher rate than desirable ones.