Astringent

An astringent substance is a chemical substance that tends to shrink or constrict body tissues, usually locally after topical medicinal application. The word "astringent" derives from Latin astringere, meaning "to bind fast". Two common examples are calamine lotion and witch hazel. Astringency is also the dry, puckery sensation caused by tannin in some wines. The tannins denature the salivary proteins, causing a rough "sandpapery" mouthfeel. A small amount of astringency is expected in some wines, especially young red wines made from powerful varieties such as cabernet sauvignon.

Astringent substances are also found in many fruits such as blackthorn, bird cherry and persimmon fruits, giving them their mouth-puckering qualities. Astringency tastes unpleasant to many mammals (including humans), which tend to avoid eating astringent fruit; conversely, birds do not taste astringency and readily eat these fruit. It is thought that fruit astringency evolved in plants because birds are better than mammals at long-distance seed dispersal (often flying some distance before passing the seeds in their droppings), so plants that contained astringent substances in the fruit are more successful than those that did not.

Astringency is a flavour characteristic in some beer. Though astringency can be a desired trait in some beer styles it is generally regarded as undesirable. It is generally acknowledged that astringency in beer is caused by a fault in the method of converting starch in malted barley grain to sugar, the process known as mashing. Astringency in beer can also be caused by a high volume of hop flowers in the beer.

Astringent medicines cause shrinkage of mucous membranes or exposed tissues and are often used internally to check discharge of blood serum or mucous secretions. This can happen with a sore throat, hemorrhages, diarrhea, or with peptic ulcers. Externally applied astringents, which cause mild coagulation of skin proteins, dry, harden, and protect the skin. Acne sufferers are often advised to avoid astringents, which are believed to worsen the clogging of pores. Astringent also helps heal stretch marks and other scars. Mildly astringent solutions are used in the relief of such minor skin irritations as those resulting from superficial cuts, allergies, insect bites, or fungal infections such as athlete's foot.

Some common astringent agents include alum, oatmeal, talc (talcum powder), witch hazel, very cold water, and rubbing alcohol eg Surgical Spirit. Astringent preparations include silver nitrate, zinc oxide, zinc sulfate, Burow's solution, tincture of benzoin,and vegetable substances such as tannic and gallic acids. Some metal salts and acids have also been used as astringents.