Tannins are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids. They are naturally occurring chemical compounds, known as polyphenols, found in many plants, particularly in the bark of oak species and in sumac and myrobalan. Tannins are responsible for the dry and puckery feeling in the mouth following the consumption of unripened fruit, red wine, or tea. They are also found in foods and beverages such as tea, coffee, dark chocolate, nuts, and wine. Tannins are present in the wood, bark, leaves, and fruit of plants as various as oak, rhubarb, tea, walnut, cranberry, cacao, and grapes.

Tannins are important in the production of leather, as they are used to tan animal hides. They are also used in the clarification of wine and beer, as a constituent to reduce viscosity of drilling mud for oil wells, and in boiler water to prevent scale formation. Tannins can be best described through the tactile sensations they produce, which is more of a mouthfeel rather than aroma or flavor. They provide texture and mouthfeel to wine as well as a sense of weight and structure. Tannins can be classified chemically into two main groups, hydrolyzable and condensed.

In summary, tannins are bitter and astringent compounds that are found in many plants and are responsible for the dry and puckery feeling in the mouth following the consumption of certain foods and beverages. They are important in the production of leather and have various industrial applications. Tannins provide texture and mouthfeel to wine and are an important component in red wines structure.