There are two processes used in soap making, i.e. hot process as well as cold process. Commercial soaps are generally manufactured using a hot process technique in which the oils and alkali are heated together to cause saponification (a method where the oils and alkali bind). During the process, the soap products and the glycerin separate. In large commercial soapmaking processes, the glycerin is taken out and sold, and the remaining mixture of soap is then formed into bars or other shapes and sizes. As the soap mixture is heated for such as long time, the oils in the hot process can go sour. So to counter souring, a complete array of chemicals are added in the hot process soaps to increase their shelf life and keep them fresher for a long time.
Handmade soap manufacturers generally use the cold process technique of soap production in which the oils are boiled just to the melting temperature and then mixed with an alkali to cause saponification. The mixture is then poured into moulds, cut and cooled off and then cured for about 4 to 5 weeks.