What is saponification?
The term saponification is the name given to the chemical reaction that occurs when a vegetable oil or animal fat is mixed with a strong alkali. The products of the reaction are two: soap and glycerin. Water is also present, but it does not enter into the chemical reaction. The water is only a vehicle for the alkali, which is otherwise a dry powder.
The name saponification literally means "soap making". The root word, "sapo", is Latin for soap. The Italian word for soap is sapone. Soap making as an art has its origins in ancient Babylon around 2500 - 2800 BC.
The oils used in modern handmade soap are carefully chosen by the soap maker for the character they impart to the final soap. Coconut oil creates lots of glycerin, makes big bubbly lather, and is very stable. Olive oil has natural antioxidants and its soap makes a creamier lather. Tallow, or rendered beef fat, makes a white, stately bar that is firm and creates abundant lather. Many other oils can be used, each one for a specific reason. Your soap maker will be glad to tell you which oils are used to make her or his soap.
The alkali used in modern soap is either potassium hydroxide, which is used to make soft soap or liquid soap
because of its greater solubility, or sodium hydroxide, which is used to make bar soap. The common term for the alkali became simply "lye", which curiously is not short for alkali, but originated in the Anglo-Saxon language.
Soap made in cottages and on farms in earlier American times became known as "lye soap". That term is now pejorative and derogatory and denotes a harsh soap that would irritate your skin. The old soap got a bad name because it had an excessive amount of caustic. Weighing and measuring techniques were crude, and knowledge of soap chemistry was elementary or non-existent.
The true fact is that modern handcrafted soap, though necessarily made with lye to get true soap, has no lye in the final product. It has all been reacted with the oils to form soap and glycerin.
A curious fact about modern soap is that most common soap found in the grocery store made in mass-produced factories does have a small amount of excess alkali in it. Also, it has had all of its naturally-occurring glycerin removed so it can be sold as a separate commodity. Why? Greater profit. An important difference between most commercial soap and our Real Handmade soap is that the glycerin is left in Real Handmade Soap and thus it retains its natural moisturizing property.
Richard Hamner, Green Mountain Soap Company