What does saponification mean? If you look up the definition you will find it explained as an exothermic chemical reaction that happens when fats and oils (fatty acids) come into contact with lye. The word itself actually means “turning into soap” and comes from the Latin root word for soap which is “sapo”.
Simply put saponification is the name of the process which yields soap.
A by-product of the saponification reaction is glycerin which is an essential ingredient in the making of soap.
Every fatty acid has what is known as a sap value. This is the amount of lye needed to convert these oils and fats into soap leaving no lye behind. Every oil has its own value. It is for this reason that recipes used in soapmaking should be run through a lye calculator in order to verify the correct amount. Vegetable oil can be used in this process in exactly the same way to make an inexpensive soap.
During the process fats and oils are hydrolyzed into free fatty acids which then combine with the alkali (lye) and as such form a crude soap. It is at this point that glycerol(glycerin) is released. The glycerol can be left in the soap or it can be washed out and then used as a very useful by-product for making handmade soaps,other cosmetic products and many other daily used items.
The history of soapmaking suggests that ancient civilizations used the cold process for making soap-like substances and were familiar with the reactions between oils and lye. The Romans, Egyptians and Greeks all produced a type of soap they would apply topically to their bodies for the treatment of skin disorders.
In soaps made at home using the cold process method there is an excess of fat used in the recipes which means these soaps are very moisturizing. This is called super-fatting. The reason we super-fat our home made soap is to ensure that all the lye is used in the saponification process.
During the cold process of soapmaking, essential oils, fragrances and colorants are added to the mixture when it has reached what is called ‘”trace'”and this is the point when saponification is sufficiently reached. Trace means the soap mixture has started to thicken and the chemical reaction will continue to completion on its own. This is the earliest point where any additives should be added to the soap mixture.
When soap is made using the hot process method, an emollient can be added as soon as the oils have saponified. This means the oils remain intact in the finished bar of soap.