Saponification is the process and result of saponifying. This verb is used in the field of chemistry to name the action of hydrolyzing an organic compound of the ester type.
To understand what saponification is, therefore, one must know the meaning of several concepts. Hydrolyzing involves causing hydrolysis: that is, splitting a molecule through water. An ester, for its part, is the compound resulting from the replacement, in an acid, of a hydrogen atom by an alcoholic radical.
These chemical processes are very important since they allow the production of soap. Through saponification, a fatty body joins water and a base to become a soap. This can be transparent (when working hot) or opaque and milky (if the process is carried out cold).
To produce soap at an industrial level, in this way, boilers are usually used where a fat material is boiled. Little by little, sodium hydroxide is added while the mixture is stirred. Thus, when saponification begins to develop, the mixture becomes pasty. The result of the process is the obtaining of soap and glycerin.
It is important to bear in mind that not all fats can be used to produce soap: this is why lipids are divided into saponifiables and unsaponifiables, depending on whether or not they are subjected to saponification.
The saponifiable lipids are those which have an alcohol - linked to one or more fatty acids. Said link is carried out through an ester link, which is very difficult to hydrolyze, although it can be easily broken if the lipid is in a basic medium; in such a case, the saponification that takes place is considered alkaline. When a neutral fat or a glyceride is used to obtain the soap, glycerin also arises, an alcoholic by-product that sometimes yields a greater benefit than the main one from an economic point of view.
The hydrophobic part of soap (that is, its hydrocarbon chain) is related to non-polar substances, such as the fatty components of foods. The hydrophilic part of the molecule (the carboxylate group), on the other hand, is related to water. Saponification results in a product whose ions are able to surround each drop of fat they encounter: the polar parts go through a solution; instead, the carbonate groups remain on the outside and are arranged. In this way, after being reduced to structures of very small size, it is possible to associate it with water molecules, thanks to which the fat is easily dispersed.
With respect to the small droplets in which there are carbonate anions surrounding nonpolar particles, they are known as micelles and have a negative charge on their surface, a feature that leads them to mutually repel each other, which prevents coalescence (that various materials form a single body) and maintains the emulsion; this is due to the existence of the anions mentioned above.
The unsaponifiable lipids, on the other hand, do not have fatty acids, so they cannot be hydrolyzed through saponification and, therefore, are incapable of producing soap.