Soap Making Process

Soap Making Process

Soap is a mixture of caustic soda and plant or animal oil and when dissolved in water, it helps in breaking away dirt from clothes and other surfaces. The origin of soap is not yet known, though Romans claim it dates back to 600BC when the Phoenicians used goat mallow and wood ash to make soap (Onyegbado, Iyagba &Offor 73). Soap is manufactured using two primary methods; kettle and continuous method. The kettle method is applied by small manufacturers and the process may last from 4 to eleven days to be complete. The quality of each batch is also considered inconsistent due to the different oils used. The continuous process is however used by large manufacturing companies and rather than production of one batch, the process is continuous. Producers have more control over the process and it is much quicker as it only lasts for 6 hours to complete one batch. This paper will focus on the kettle process of soap manufacturer that can be conducted even at home.


The primary raw materials required are alkali and fat. The most common type of alkali used is sodium hydroxide and sometimes potassium hydroxide (Onyegbado, Iyagba &Offor 73). Potassium based soaps are preferred since they are water soluble as compared to sodium based ones. In the past, animal fat was applied directly to the process but today manufacturers use processed fatty acids that are known to eliminate impurities and also produce glycerin as a final by-product (Onyegbado, Iyagba &Offor 73). One can also use olive oil, vegetable fat coconut oil, or palm kernel oil for the process. Additives such as perfumes, fragrances are also added to enhance the color and smell of soap. Abrasives use to enhance the texture of the product include silica, talc, and volcanic ash. Soap that is manufactured without dye is often brown or dull grey in color but the color can be improved through use of different dye color.

The Kettle Process

The Boiling– The process starts with melting of alkali and fats in a kettle, a steel tank that is partitioned three times and can hold a thousand pound of raw materials and products (Onyegbado, Iyagba &Offor 73). There are steam coils placed inside the kettle to enhance the boiling. After reaching boiling point, the fat and alkali react producing glycerin and soap.

Salting– The raw materials that are placed into the kettle contain parts of lye’s that assist in initializing the saponification process and reaction. Once saponification is complete, the glycerin and soap are separated through mixing with salt, a process known as soap graining. The soap rises to the top and the glycerin, water, and NaOH that are inexcess settle at the bottom where it is extracted through taps (Onyegbado, Iyagba &Offor 73).

Strong change– To eradicate the small fat amounts that are not yet saponified, a strong caustic solution is mixed into the kettle in a process known as strong change. The mixture or mass is then boiled again to ensure the last bits of fats turn to soap. At this point, the manufacturer may decide to repeat the soap treatment or proceed with the steps if satisfied.

Pitching– The final step is known as pitching and the soap is boiled again with water being added to separate the mixture into two layers. The top layer is known as neat soap and contains 30 percent water and 70 percent soap. The bottom layer is known as the nigre and contains impurities removed from the soap such as salt, water, and dirt. The neat soap is removed and put into molds for cooling and hardening into slabs. The cooling process can also take place in special freezers. The big slabs can then be cut into smaller sizeable pieces or bars that are then wrapped and stamped. This process takes several days unlike in the continuous that only takes few hours.

In the last pitching process, after the soap is boiled again with water, the mass separates inside the partitioned kettle into the various components of neat soap, nigre, water, and salt. All the products are placed at different levels in the partitioned machine and therefore do not mix and are easily extracted. The primary by-products of the process are glycerin which is used in making hand and body lotions and nitroglycerin that is adopted as an explosive component, for example, dynamite.


Jessica Wang



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