Tannin is a substance found in many different plants. Tannin is notably found naturally occurring in grapes, tea leaves, and oak. The word tannin comes from the historical practice of using the tannin found in oak bark to tan leather, although in the modern world, synthetic is usually used for this purpose instead.

Tannin is found in the skins, seeds, and stems of grapes. Wine that is fermented while still in contact with these parts of the grape – red wine – absorbs a quantity of tannin, which lends a distinct character to the wine. Because the tannin in the seeds of grapes is particularly harsh, wine is usually crushed rather than pressed, to minimize the absorption of seed-based tannin. Many wines also absorb some tannin from the oak barrels they are aged in, which lends additional flavor to the wine.

Tannin is crucially important to the complexity of a wine and how well it will age over time. High tannin wines tend to age best for long periods of time, such as those made from the Cabernet Sauvignon, Nebbiolo, and Syrah grapes. Wines that have a great deal of tannin in them when young often seem searing, creating a sensation of dryness in the mouth, particularly the roof of the mouth. The most tannic of wines cause the mouth to pucker, which is not a pleasant experience.

Over time, however, the tannin acts as a preservative and mellows, helping the wine to grow into its complexity and become truly exceptional. A well-made, high-tannin wine, which may be virtually undrinkable when young, can become a masterpiece of a wine later in life. That said, many wines are simply too tannic, and by the time their astringency fades, the wine will have passed its prime.

One thing that can help with wines that possess a high amount of tannin is to combine them with high-fat and protein foods. Milk fits this role ideally, helping to soften the sharp edges of the tannin. This is one reason so many people add milk to strong teas, which are also very high in tannin. Good cheeses or a hearty cream sauce can turn a wine that at first blush appears too tannic into the perfect pairing.

In general, the trend in winemaking is towards wines with less tannin than fifty years ago. These wines are easier to drink upon purchase or within a short year or two after buying them, and so are more suited to the new global wine market. To be well-rounded in the world of wine, however, it is a good idea to sample a number of high-tannin wines, to taste the nuance that this substance can add.