tannins, diverse and complex group of chemical compounds that occur in the bark of many trees and in fruits, including the grape. Strictly speaking, a tannin is a compound that is capable of interacting with proteins and precipitating them; this is the basis of the process of tanning animal hides (hence the name tannin) and is also a process that is believed to be responsible for the sensation of astringency. Tannins in wine come predominantly from the grapes and, to a much lesser extent, from the wood in which the wine is aged. See also oak flavours.
