Tannin is a natural substance that can be found in plants. Many people confuse it with “tanning”—and the similarity in the words are no accident. Centuries ago, the tannin in oak bark was used to for tanning leather. Today, however, the leather manufacturing process uses synthetic materials instead.
Tannin, however, is an important consideration in making wine. It is found in great abundance in grapes, particularly the seeds, stems and even the skins. Unfortunately, the tannin has a very distinct flavor. Too much of it can alter the flavor and make it far too harsh. One sign of too much tannin is that the mouth puckers, and feels too dry—some report a “searing” sensation. To avoid this, wineries prefer to crush rather than press wine. However, the tannin in oak can add a particular flavor, too—and to add to the “depth” of the wine, it is common for it to be aged in oak barrels.
Different kinds of grapes have different levels of tannin. For example, Syrah and Cabernet Sauvignon have particularly high amounts. Wines that have a high amount of tannin need to be aged for long periods, so the flavor will become more mellow and ultimately more complex and delicious.
Tannin can also be found in tea leaves. To “soften” the tannic flavor it is possible by to high-fat and high-protein ingredients such as milk. This may explain why it is a popular practice to add milk to a very strong tea. It is also the principle behind pairing high tannic wines with cheeses or dishes with cream sauce.