The industrial production of soap involves continuous processes, involving continuous addition of fat and removal of product. Smaller-scale production involve the traditional batch processes. There are three variations: the cold-process, wherein the reaction takes place substantially at room temperature, the semi-boiled or hot-process, wherein the reaction takes place at near-boiling point, and the fully boiled process, wherein the reactants are boiled at least once and the glycerol recovered. The cold-process and hot-process (semi-boiled) are the simplest and typically used by small artisans and hobbyists producing handmade decorative soaps and similar. The glycerine remains in the soap and the reaction continues for many days after the soap is poured into moulds. The glycerine is left during the hot-process method, but at the high temperature employed the reaction is practically completed in the kettle, before the soap is poured into moulds. This process is simple and quick and is the one employed in small factories all over the world.
Handmade soap from the cold process also differs from industrially made soap in that an excess of fat is used, beyond that which is used to consume the alkali (in a cold-pour process this excess fat called “superfatting”), and the glycerine left in acts as a moisturizing agent. However, the glycerine also makes the soap softer and less resistant to becoming “mushy” if left wet.