Wine is fermented grape juice. Alcohol is produced by the action of natural (present on grapes' skins) or industrial (cultivated) yeast on sugar from the grape juice. Gas (Carbon dioxide) and heat are also produced in the process. After this transformation the winemaker will operate or not an other fermentation to reduce the acidity if required (malolactic fermentation). Then the wine will be bottled directly or aged in oak barrels to add some other components (more tannin and vanilla/toasty aromas from the wood). The wine will also developp other flavours and become a bit more oxidized thanks to some contact with oxygen circulating throught the porous wood.