The aromas due to barrel aging fall under the category "tertiary" aromas: those that develop last in a wine, therefore during the aging phase, whether this occurs in the barrel or in the bottle. They are called tertiary precisely because they develop temporally after those typical of grapes (primary/varietal aromas) and after those due to fermentation (secondary aromas).
Tertiary aromas add complexity to the wine bouquet, when they are not too marked or unpleasant, and enhance the primary and secondary aromas without suffocating them. This case refers to a ready or mature wine, while when the primary and secondary aromas tend to disappear we are speaking of an “old” wine, which has now passed its best moment.
During aging, wine aromas evolve due to various factors: oxidation of the wine, the transfer of aromas and other chemical substances from the barrel wood, the absorption by the wood of some fermentative/fruity aromas of the wine, and chemical reactions that develop over time within the wine.
The oxidation of wine can occur both in the bottle, in fact corks are permeable to small quantities of oxygen sufficient to make the wine "mature", and in the barrel. The oxidation aromas in white wines can be honey, wax, resin, overripe apple, walnuts and dried figs. In red wines, they can be plum, cooked fruit, jam, dried fruit.
Barrel aging, in addition to allowing oxidation, enriches the wine with a series of aromas contained in the wood. The aromas conferred by the barrel are: vanilla, coconut, bread crust, coffee, caramel, smoked, cloves, hazelnut, wet straw, leather, spiced wood, licorice. The barrel aging process also has different effects on the wine depending on the characteristics of the wood and the process used:
- Small barrel (Barrique - 225 liters) vs. large barrel (several hectoliters): the small barrel releases a greater amount of aromas and allows a more controlled oxidation.
- New barrel vs. old barrel: the new barrel contributes with a greater quantity of chemical substances and therefore of aromas.
- Area of origin of the wood: for example, American oak aromas are more spicy and French oak aromas tend toward vanilla.
- Type of wood toasting.
- Wood processing.
Finally, during the barrel aging process, some of the fruity/fermentative aromas of the wine are absorbed by the wood, causing those aromas to lose intensity. Some wine varietals are better suited than others to be aged in barrels because they maintain the fermentation aromas well: Merlot, Cabernet Franc, Cabernet Sauvignon and Pinot Nero, for red wines; Chardonnay and Sauvignon Blanc, for white wines.