Saponification in the Soap Making Process

Illustration of hands pouring soap

Illustration: The Spruce / Michela Buttignol

Saponification is at the heart of soap making. It is the chemical reaction in which the building blocks of fats and oils (triglycerides) react with lye to form soap. Saponification literally means "turning into soap" from the root word, sapo, which is Latin for soap. The products of the saponification reaction are glycerin and soap. Chemically, soap is a fatty acid salt.

How Saponification Happens

Soap making requires careful measurements as you are using chemicals, some of which can be dangerous. Soap making is a simple process and it's likely you have many of the ingredients and tools already in your kitchen.

Saponification is an exothermic (gives off heat) chemical reaction that occurs when fats or oils (fatty acids) come into contact with lye (a base). In this reaction, the triglyceride units of fats react with sodium hydroxide or potassium hydroxide and are converted to soap and glycerol. For some types of soap, salt is then added to precipitate the solid soap.

The saponification generally takes about 24 to 48 hours to complete once the lye and oils have been mixed and the raw soap has been poured into the mold. This process can be sped up by adding more heat or slowed down by keeping the process very cool.

Soap Making Calculator

Oils and fats each have what is called a “saponification value,” which is the amount of lye needed to completely neutralize them into the soap with no lye left over. Each oil has a different value, which is why it’s important to always run soap recipes through a lye calculator. The calculator will help ensure that the ratios of water, oils, and lye are correct and will produce the results you are looking for.

Ingredients

There are many variables that will impact saponification and different soap ingredients have very distinct characteristics. Be sure to research the types of acids you are using (ex: coconut oil, olive oil, etc.) and the results they may have on the final soap product. Depending on the ingredients used, soaps can vary greatly with different attributes such as lather, bar consistency, and cleansing ability.

Most of the ingredients for soap making can be found in a grocery or hardware store. Be sure to buy pure high-quality lye that is made specifically for soap making. In addition to the basic soap ingredients, there are many options that can be added to the soap to alter the fragrance, consistency, and color of the soap. Once the basic soap making has proven successful, try experimenting with other soap variations.

Storing the Soap

Homemade soap should be left to air dry for approximately four to six weeks. This is known as the curing time and it will allow for any excess water to evaporate out of the soap. It's best for the soap to be in a cool, dry location, not touching anything else, while it is drying. A shoe box in a dark closet is a perfect location. If the homemade soaps contain any fragrances, store each fragranced soap in its own box so the scents do not mix. Once the soap is cured, be sure to label it with the ingredients used and the date the soap was made.