The Magic of Saponification: How Soap is Made

Have you ever wondered how a bar of soap transforms from a mix of oils into the fragrant, cleansing product you use every day? The answer lies in a fascinating chemical reaction called saponification.

What is Saponification?

Saponification is the process that turns fats or oils and a strong base into soap and glycerin. The term comes from the Latin word sapo, meaning “soap,” and it’s been known for centuries. Ancient civilizations like the Babylonians and Egyptians were already experimenting with soapmaking thousands of years ago.

The Chemistry Behind It

At its core, saponification is a chemical reaction between a triglyceride (fat or oil) and a strong base - typically lye (aka sodium hydroxide.

Here’s a simplified version of the reaction:

Fat/Oil (Triglyceride) + Sodium Hydroxide → Soap + Glycerol

Triglycerides are esters derived from glycerol and three fatty acids. When the strong base is added, it breaks the bonds holding the fatty acids and glycerol together. The fatty acids then react with the base to form soap (a salt of a fatty acid), and the glycerol is left as a by-product.

The Soap Making Process

1. Choosing Fats and Oils: Different oils bring different properties. Olive oil makes a moisturizing soap, coconut oil contributes hardness and lather, and palm oil adds stability.

2. Preparing the Lye Solution: Sodium hydroxide (lye) is carefully mixed with water. This step must be done cautiously, as the solution gets very hot and is caustic.

3. Mixing: The lye solution is combined with the oils. As the mixture emulsifies and begins to thicken - a stage known as “trace” - the saponification reaction starts.

4. Curing: After being poured into molds, the soap needs time to fully saponify and cure. This can take several weeks, during which excess water evaporates and the soap hardens.

Why Glycerin Matters

Glycerin, the by-product of saponification, is a humectant, meaning it attracts moisture to the skin. In our soaps the glycerin is retained, giving the soap its moisturizing quality. In commercial soapmaking, however, glycerin is sometimes removed and sold separately for use in lotions and creams.