The most common types of wine aged in oak barrels are red wines.
After fermentation, and prior to bottling, some wines are matured (or ‘aged’) in oak barrels. The aging process may take upwards of 12 months, and allows tannins in the oak barrels to add flavor and character to the wines.
An additional process – refining (or ‘fining’) – takes places while wines age in their barrels. During fining, sediments are separated out and removed from the wine. Also, wine may be siphoned from one barrel to another, a process known as ‘racking’. During racking, wine is separated from additional sediment at the bottom of the barrel.
Red wines contain higher tannins than do white wines. Thus, the introduction of additional tannins from oak casks is thought to only improve the character and flavor of a red wine. On the other hand, white wines, low in tannins and softer in character, could be overpowered by the oak tannins. For this reason, few white wines (such as Chardonnay) are matured in barrels.