About 99 percent of the wine produced in the world is meant to be consumed young and is not intended to be aged. The compounds in wine that allow it to be aged are tannins, acidity, and alcohol, which act as natural preservatives. Tannins are substances found in grape skins and seeds, as well as in young oak barrels. Acid is a natural substance in grapes and is what gives wine its brightness. Alcohol is an antiseptic.
With age, wine will have changes in color, aromas, and flavors. Wine corks are porous and gradually let some air into the wine allowing gradual oxidation to occur. When you cut an apple or an avocado and leave it for a little while, there is a reaction between compounds in the fruit and the air, and it browns. This is the same type of oxidation that occurs in wine. If you’ve ever been told to take apple slices and dunk them in a combination of water and lemon juice to prevent browning, that is an example of how acid acts as an antioxidant, and helps to prevent rapid aging. The same applies to wine.
With age, white wines will turn darker from yellow to a golden-brown. The lower the acidity level, the faster the color change will occur. The most age-worthy white wines are those will high acidity levels. These are usually from high-acid grapes, especially if they are grown in cool climates, as the lower temperatures slow down the loss of acidity as the grapes ripen. White wines that age well are those made high-acid grapes, like Riesling, Chenin Blanc, and Semillon. Chardonnay from Burgundy, a cool climate, retains its acidity well, making these wines age well also. White wines aged in younger oak barrels, like White Rioja and warmer-climate Chardonnay, will age due to the tannins extracted from the oak during barrel aging.
Aging red wine will cause color pigments to fade and wines will become lighter, more translucent and more brick in color, due to oxidation. Also, color pigments and tannins in red wine will join together over time, and form larger particles called polymerization. These particles will fall to the bottom of the bottle, reducing the color and the tannins of the wine as they form a sediment.
Wines, with age, show a reduction in the aromas of the fresh fruit that were present, if the wine had been opened and drunk early. Fruitiness is replaced by dried fruits or even stewed fruits. Floral notes may yield aromas of dried flowers with age. Aromas that weren’t detected or strongly evident in the wine’s youth will appear like honey, earth, soil, mushrooms, and savory notes. Some of these aromas will come from the winemaking itself, but weren’t detectable due to the prominent fruit characteristics.
Similar to the changes to the aroma of wine, wine flavors change too. The primary flavors the wine had when first released fade and are gradually replaced by more flavors that come from aging, but also barrel aging, like vanilla, cocoa, leather and dried tobacco. The tannins are also softer.
Wines made from red grapes that have the ability to age include grapes like Nebbiolo, Aglianico, Cabernet Sauvignon, Tempranillo, Sangiovese, Merlot, Syrah, and Malbec. Pinot Noir can be aged, especially if it is from Burgundy, due to the climate and the ability to retain acidity.
A final note is that sweet wines age beautifully, too, because the grapes used are very high in acidity, to be in balance with the sweetness. Sweet wines that can be well aged include Recioto della Valpolicella, Tokai Aszu from Hungary, German Rieslings, Alsatian Rieslings, and French Sauternes.