Soaps are made from naturally occurring animal fats and vegetable oils. The animal fats and vegetable oils are esters of the alcohol, propane-1,2,3-triol (glycerol) CH2OHCHOHCH2OH and long chain carboxylic acids (often known as fatty acids) RCO2H, where the alkyl groups contain between 7 and 21 carbon atoms.
The fats and oils are heated with an alkali, usually sodium hydroxide, and the esters are hydrolyzed to form a sodium salt of the carboxylic acid and the alcohol, propane-1,2,3-triol (glycerol):
The process is known as saponification and the sodium salts of the acids are soaps.
The soap is dried by spraying into a vacuum chamber to give a final product suitable for stamping.
In order to give those properties to the soap the public seek, it is manufactured from a blend of animal fats (tallow) and vegetable oils (coconut and palm kernel). Some pure vegetable soaps are available, manufactured by substituting palm oil for tallow as the triglycerides have sufficiently similar composition. These are most likely to be manufactured in tropical countries where the vegetable oils are more readily available than are animal fats.
Some high quality soaps contain un-neutralised fatty acids. These help to stabilise the lather and improve the feel of the soap on the skin.
Traditional bar soaps are being increasingly replaced, particularly in developed markets, by liquid products such as shower gels, body washes and 'liquid soaps' that are formulated using synthetic surfactants rather than soaps.
Date last amended: 18th March 2013