How are soaps made from fats or oils and sodium hydroxide?

Soaps are produced through a chemical process known as saponification, which serves as the foundation for all soapmaking.12

In this reaction, a hot caustic alkali solution—typically sodium hydroxide (caustic soda)—is applied to natural fats or oils, such as tallow or vegetable oil. This interaction converts the fats into sodium fatty acid salts, which constitute soap, along with glycerin (or glycerol) as a by-product.12

While traditional methods involved a time-consuming boiling process, modern industrial production often utilizes a continuous hydrolyzer process. In this method, natural fats are first split into fatty acids and glycerin using high-temperature water and a catalyst. The resulting fatty acids are then distilled for purification and neutralized with sodium hydroxide to yield soap. Using pre-processed fatty acids instead of raw fats allows for more precise control and eliminates the need to remove glycerin or impurities from the final product.32