A catalyst is a substance which accelerates the rate of a chemical reaction, but remains unaltered by the reaction.

In the oils and fats industry the main use of catalysts is in the hydrogenation process where nickel and very rarely copper chromite are used and in interesterification and trans esterification (bio diesel production) where sodium methoxide is the usual catalyst. It is essential that no traces of these catalysts pass accidentally into the finished deodorised oil, as they will also accelerate its oxidation. Testing for absence of these impurities is one of the tasks undertaken by the laboratories of the major food companies.