>And what does “better” even mean?
That’s entirely subjective.
Also, most wines are only aged for 2-4 years, this, for the most part, allows fermentation to continue at a very slow pace, which for reasons that aren’t well understood, produces a more complex and more mellow flavor. It probably has something to do with the yeasts in the barrel slowing dying then sinking to the bottom. After 3 years or so, further aging is usually considered to slowly deteriorate the flavor. A 12 year old bottle of white wine probably won’t taste as good as a 4 year old one. It will probably taste more like vinegar.
Only some kinds of red wines under some conditions, improve over 10-20-30 years of aging.
First of all, wine barrels are made of toasted white oak. During aging, the wine slowly absorbs some of the woody, toasted, smoky flavors from the oak.
In the case of barrel aging, wood barrels aren’t completely airtight. They allow a small amount of oxygen to enter, and they allow water and alcohol to slowly evaporate. Which concentrates some of the flavors.
The slow entrance of oxygen allows bacteria and yeasts in the wine to oxidize some of the flavor chemicals in the wine that may be considered unpleasant. Meanwhile this produces flavors associated with oxidation sometimes described as being similar to cured tobacco. This also allows some fermentation to continue, producing more yeasty, savory flavors. Oxidation also breaks down some of the tannins found in the grape skins and in the oak wood, which reduces bitterness and astringency.
Some white wines are, instead, aged in large stainless steel tanks. The absence of oxygen better preserves the fruity flavors from the white grapes.
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