Fumaric acid is added to certain desserts to give them a more intense aftertaste, according to P. Michael Davidson, author of "Antimicrobials in Food, Third Edition." Gelatin desserts are one example of foods that contain fumaric acid to make the aftertaste more flavorful, as well as to help strengthen them. Pudding, sherbet, sorbet and desserts made with condensed milk can also contain fumaric acid. In addition, some pie fillings can contain fumaric acid, Davidson notes.