Wine undergoes a period of aging following fermentation. This lets the wine mature, giving well integrated characters that very young wines tend to lack. Most wines receive some sort of barrel storage or exposure to wood alternatives during ageing as it imparts desirable sensory properties. Ageing is a critical time during wine processing as chances for spoilage and flaws to develop increase while the wine sits in storage. Winemakers must decide whether to use barrels to age their wine, what type of barrel to use, and what protocol to maintain quality is employed during the ageing period. Finally winemakers must decide when the wine is done ageing and ready to package as finished wine.

White wines are typically aged for shorter periods of time as they have more delicate flavors and do not possess the tannins that allow red wines to potentially age for decades. Lighter, crisper styles are often prevented from undergoing malolactic fermentation to retain more acidity and aged with little or no wood exposure. Richer white wines are often given sur lie ageing in barrel.

Red wines are commonly barrel aged and stored for more extended periods than white wine before finishing. This extended period is often needed to allow mature flavor development in the tannins extracted during fermentation.

Specialty wines such as sparkling wine and fortified wine can require extended periods of ageing to allow integration or development of flavors typical to the style of the wine. Tawny Port for instance can be aged for 40 years or more for certain styles.

Barrel ageing requires some routine processing and monitoring to insure wine quality. Barrels will evaporate a small amount of liquid over time and require topping. Lees can develop reductive characters if not routinely stirred to provide small amounts of oxygen. Sulfur dioxide levels must be maintained to prevent spoilage. Wines may need to be occasionally racked, and the barrels themselves often require some maintenance.