Wines with high sugar contents (Sauterne, Barsac, Late Harvestwines, Eisenwine) and those fortified with alcohol (Port, Sherry) can last for many years in the cellar and continue to improve. Wines which have passed their optimum age can display off-colors (in white wines they tend to appear more golden, yellowed, or even a brownish tint, while in red wines they take on a decided brick-red hue tending toward brown) and non-pleasing odors.
The chemistry of aging is still not completely understood. However, we do know that while in the cask the wine tends to smooth out and breathe through the natural process of oxidation that occurs. It is during this time that the natural flavors and aspects of the wine tend to come together (“marry”). Still more changes occur when the wine is in the bottle, the most prominent being the development of the wine’s bouquet (a by-product of what are called “aromatic esters” and other chemical compounds which are not normally found in young wines).