Fumaric acid is a compound with the chemical formula HO2CCH=CHCO2H and the CAS Number 110-17-8. It is also referred to as trans-butenedioic acid, and its preferred IUPAC name is (2E)-But-2-enedioic acid. It has a white crystalline form and occurs in the natural world. It is key to organic acid biosynthesis in mammals and plays a critical role in plant life, and it can be naturally found in abundance in Iceland moss, lichen, and bolete mushrooms. When it comes to sourness and titratable acidity — or TA — fumaric acid is one of the strongest food acids available. Its uses as an additive span the manufacture of everything from pie fillings and animal feed to medicines and even cleaning agents for bath salts and dentures.