Fumaric acid or trans-butenedioic acid is the chemical compound with the formula HO2CCH=CHCO2H. Fumaric acid has a fruit-like taste and has been used as a food acidulant since 1946. Fumaric acid does not combust in a bomb calorimeter under conditions where maleic acid deflagrates smoothly. For teaching experiments designed to measure the difference in energy between the cis- and trans- isomers, a measured quantity of carbon can be ground with the subject compound and the enthalpy of combustion computed by difference.