ABSTRACT
I. INTRODUCTION Processing seeds or animal tissues into edible oils can be broken into four sets of operations: recovery, refining, conversion, and stabilization. Oil recovery is often referred to as extraction or crushing when processing plant sources and rendering in the case of processing animal tissues. Oil extraction involves pressing the oilbearing material to separate crude oil from the solids high in protein or washing flaked or modestly pressed material with solvent, almost always hexane. The defatted solids after pressing are known as cake and after solvent extraction as meal. The oil, crude oil because it contains undesirable components, such as pigments, phosphatides, free fatty acids, and off-flavors and off odors, must be refined to remove these contaminants and produce high quality edible oils. Refined oils consist primarily (>99%) of triglycerides and can be converted, usually by hydrogenation; but winterizing, fractional crystallization, and interesterification should also be considered conversion processes because they achieve different properties from the original oil, such as converting liquid oil into semisolid or solid fats. Plasticizing, tempering, and stehling are operations designed to stabilize crystal-oil mixtures used for shortenings and margarines.
