Simply put, a barrel-aged wine is one that has been aged in a barrel—presumably oak—after going through the fermentation process. You'll see this term most often on the back label of fine wines, and it's a good indication that the wine may have taken on some of the vanilla, oak, butter, and other characteristics from the oak. Barrel aging also gives wine a deeper color and softens its tannins as oxygen slowly creeps through the wood's pores. When the vintner determines that a wine has been barrel aged long enough—yes, you can over-oak a wine—he or she then bottles it and, in some cases, lets it age even further. An aside, most wineries use a combination of new, one-year-old, two-year-old, and three-year-old barrels. They aim to replace their oak barrels after four or five vintages, since by then the insides become encrusted with deposits that prevent interaction between the wood and the wine. See also barrel-fermented.