What is saponification? Saponification can occur in nature with animal and even human corpses (adipocere). It can even cause damage to oil paintings causing soap lumps to bloom in famous works of art. But with respect to making the soap making it’s the way we turn fat (or oils) into glycerol.
Lye is a strong base and we don’t want to be washing with it. But when mixed with fat/oils it turns to glycerol. This process is called saponificiation. Glycerol sounds nasty but it is a really helpful healthy product. Glycerol has many different functions in our day to day life. In foods it is a way to keep things moist, can act as a sweetener, and even a preserver of foods. Glycerol is used in pharmaceuticals like cough syrups, mouthwashes, shaving creams and soaps. In soaps it is the cleaning agent for glycerin soap. With this type of soap essential or natural fragrance oils are normally added for fragrance. This kind of soap is used by people with sensitive, easily irritated skin because it prevents skin dryness with its moisturizing properties. It prevents excessive drying and evaporation and is a truer form a cleaning like our ancestors have used for thousand of years.
When making soap we start with a fatty acid (Triglyceride). If you have sensitive skin or care about the type of products used on your body I recommend a natural fatty acid like coconut, olive, or palm oil. I’ve heard goat’s milk or colostrum works great as well. A different amount of lye is used depending on the type of oil being used and what type of properties the soap maker wants to produce.
In order to neutralize the fatty acid an alkali (lye) is added. Some who wonder what is saponification will also ponder if it is necessary, and if it is healthy. Our answer is that it is a natural process and gives your soap the moisturizing properties and naturals oils it needs. There are other acids like lauric acid, linoleic acid, palmitic acids that are naturally in oils and is the reason the Romans would use oils and scrappers to clean with. But without saponification and the glycerin it produces these oils might pass you off for a Roman but wouldn’t wash you or keep you as clean as you have been your whole life.