Fumaric acid or trans-butenedioic acid, is the chemical compound with the formula HO2CCH=CHCO2H.
This white crystalline compound is one of two isomeric unsaturated dicarboxylic acids, the other being maleic acid, wherein the carboxylic acid groups are cis. It has a fruit-like taste. The salts and esters of fumaric acid are known as fumarates.
Fumaric acid is a food acidulent. It is non-toxic. It is generally used in beverages and baking powders for which requirements are placed on purity. It is generally used as a substitute for tartaric acid and occasionally in place of citric acid, at a rate of 1.36 g of citric acid to every 0.91 grams of fumaric acid to add sourness, similar to the way malic acid is used. It is also used as a coagulant in stovetop pudding mixes.
Fumaric acid is also used in the manufacture of polyester resins and polyhydric alcohols and as a mordant for dyes.