tannins

Compounds present in dark-coloured sorghum, carob bean, unripe fruits, tea, etc.; they have an astringent effect in the mouth, precipitate proteins, and are used to clarify beer and wines. Also called tannic acid and gallotannin.

Soluble, astringent substances found in some plants, including tea and coffee. Tannins are added to a variety of processed foods, including ice-cream and caramel. They are also used as clearing agents to precipitate proteins in wines and beer.

Tannins are sometimes called ‘antinutrients’ because they may reduce the absorption of some minerals. Drinking more than two cups of tea or coffee without milk a day can rob the body of significant amounts of calcium and iron, and may contribute to the development of osteoporosis (brittle bone disease) and anaemia. These adverse effects can be reduced by drinking tea and coffee between rather than during meals, and the addition of milk or lemon juice neutralizes the effects of tannins on iron absorption. Eating foods rich in vitamin C helps to counteract the effects of tannins on iron absorption.

[TAN-ihns] Any of a group of astringent substances found in the seeds, skins, and stems of grapes, as well as in oak barrels, particularly new ones. Tannins are part of a grouping technically called phenolic compounds. They are important in the production of good red wines because they provide flavor, structure and texture and, because their antioxidant traits contribute to long and graceful aging. Tannins often give young wines a noticeable astringency, a quality that diminishes as the wine ages, mellows, and develops character. Wines with excessive tannins are referred to as tannic. See Glossary of Wine Tasting Terms, page 613.

Secondary plant metabolites, probably important in anti-herbivore defense; divisible into the common condensed tannins, and less common and more toxic hydrolyzable tannins, e.g. gallotannins in oak trees, punicalagin in Terminalia oblongata, capable of damaging the kidneys; condensed tannins bind to protein, interfere with the availability of proteins from feeds, and are pooly absorbed from the gut.