The better wines are aged in oak, and the barrels are discarded after a few years, usually by selling them to down-scale wineries that can't afford the price of new oak barrels. The barrels here cost about €800, 1000 USD. What this means is that when you buy a bottle of really good wine a goodly chunk of the price is for the barrel in which it was aged.
The control exercised over these barrels is 'fine detail'. The wine-maker knows what this barrel was used for last year and the year before that. They taste the wine over the course of its fermenting so they can estimate how well the tannins are leeching into the liquor.
It is this delicate control that makes the difference between a good wine and a great wine.