What is the role of tannins in wine?

Tannins play a crucial role in the structure and aging potential of wine. They are polyphenolic compounds found in the skins, seeds, and stems of grapes, as well as in oak barrels used during the aging process. Tannins provide the backbone of red wines, giving them astringency and a sense of body and complexity.

The presence of tannins is particularly important for the aging process of wine. As wine ages, tannins can mellow, allowing for a more integrated and smooth mouthfeel. This softening process contributes to the development of secondary flavors that can emerge in aged wines, enhancing the overall taste experience. Wines with a good tannin structure often have a better potential for aging, as tannins protect the wine from oxidation and spoilage while allowing the flavors to evolve over time.

In contrast, enhancing sweetness, adding fruitiness, or increasing acidity do not pertain to the primary function of tannins. Sweetness is primarily affected by residual sugars, fruitiness comes from the variety of grapes and fermentation process, and acidity relates to the grape's natural acid content. Therefore, tannins' contribution to structure and aging potential is what makes choice B the correct answer.