Did You Say Getting Old Was A Good Thing?

No, maybe not for humans, but for wine sure! When a wine ages, there is a reduction in Astringency. Astringency is responsible for a bitter taste and making the mouth feel dry. Tannins contain this astringent which are naturally occurring compounds that exist inside grape skins, seeds and stems.

Young wines contain a good amount of polymerized tannins, which usually taste harsh as opposed to aged wines that are more smooth tasting. This is due to the fact that when tannin molecules polymerize this causes astringency, so as the wine ages the tannins are no longer polymerized.

The reaction below represents the wine making process from a polymerized tannin to a sulfonated tannin by the addition of bisulfite (HSO₃^-). These bisulfite ions attack the polymerized tannins, thus breaking them apart leaving sulfonated tannin as the byproduct.

A study published in the Journal of Agricultural and Food Chemistry, analyzed the tannin profile of three wines using different amounts of bisulfite. The wine with the greatest amount of bilsfulte had the least polymerized tannin leading to the least bitter wine of the three. Results are shown below.

Additionally, tannins are also indirectly responsible for a wine’s smell through reactions with the wine’s alcohols and esters to gradually subdue the flowery, fruity aromas of youth. The winemaker controls how long the mashed grapes stay in contact with the tannin-loaded stems, skins, and seeds which thus determines the amount of tannins that go into the wine. Starting off with a more bitter, dry wine will mature successfully over time.

For those interested in collecting wines over time, it is best to do so in a refrigerator set to 55°F as too much heat will cause the wine to oxidize which causes the wine’s pigmentation, aroma, and flavor to decrease.

Sources:

https://www.acsh.org/news/2018/09/08/chemistry-why-aged-red-wines-taste-better-13394

https://www.winemag.com/2018/09/11/tannins-wine-guide/