Soapstock is one of the products obtained in the industrialization of biodiesel, formed during the neutralization stage of the chemical refining of crude oil. It is formed by free fatty acids present in the oil, which are neutralized by adding an alkali solution, resulting in soaps. Due to the content of saponified fatty acids, the lees is an important raw material for obtaining a concentrate of free fatty acids, widely used in animal feed production due to its nutritional properties.