tannin

Tannin refers to a broad class of polyphenolic compounds produced by many plants. They are characterized by their high molecular weight and their ability to bind proteins and other macromolecules, which can impart bitterness, color changes, and astringency to foods and beverages.

There are two main groups of tannins. Hydrolyzable tannins consist of gallic or ellagic acid esters attached to a sugar core, typically glucose, and can be hydrolyzed to their constituent acids. Condensed tannins, also called proanthocyanidins, are polymers formed from flavan-3-ol units and cannot be easily hydrolyzed.

Common sources include bark, wood, leaves, fruit skins and seeds, and husks. Tannins are historically important in leather tanning, where they extract fibers from hides. They also contribute flavors and antioxidant properties to foods and drinks such as wine, tea, cocoa, grapes, berries, nuts, and certain fruits.

Properties vary by structure, but tannins are generally soluble to some degree in water or alcohol and produce astringency by precipitating salivary proteins. They can chelate metals and act as antioxidants; their color and reactivity can change during processing and aging.

In plants, tannins serve defensive roles against herbivores and pathogens, offer UV protection, and influence seed dispersal strategies. In foods and beverages, they affect mouthfeel, color stability, and aging dynamics, notably in wine and tea.

Health considerations include potential antioxidant benefits, but excessive intake can reduce the availability of certain minerals and proteins. Effects are dose- and context-dependent.