What is Saponification in Soap-Making?

Illustration of hands pouring soap

Illustration: The Spruce / Michela Buttignol

Saponification is at the heart of soap-making.

What Is Saponification?

Saponification is "the process in which triglycerides are combined with a strong base to form fatty acid metal salts during the soap-making process. The distribution of unsaturated and saturated fatty acid determines the hardness, aroma, cleansing, lather, and moisturizing abilities of soaps."

In other words, saponification is the chemical reaction during the soap-making process in which the building blocks of fats and oils (triglycerides) react with lye to form soap.

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

Saponification is an exothermic chemical reaction—which means that it gives off heat—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 cold.

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.

Impact of Ingredients

There are many variables that will impact saponification and different soap ingredients have very distinct characteristics. Be sure to research the types of fatty acids you are using (for example, 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 shoebox 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. 


Article Sources
The Spruce Crafts uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. The Effects of Cold Saponification on the Unsaponified Fatty Acid Composition and Sensory Perception of Commercial Natural Herbal Soaps. Molecules. 2018 Sep; 23(9): 2356. doi:10.3390/molecules23092356