At the center of a hydrolyzable tannin molecule,
there is a carbohydrate (usually D-glucose). The
hydroxyl groups of the carbohydrate are partially
or totally esterified with phenolic groups such as
gallic acid (in gallotannins) or ellagic acid (in
ellagitannins). Hydrolyzable tannins are
hydrolyzed by weak acids or weak bases to
produce carbohydrate and phenolic acids.
Examples of gallotannins are the gallic acid esters
of glucose in tannic acid (C76H52O46), found in
the leaves and bark of many plant species.