The Story Of How Soap Is Made

All you need to obtain soap is to mix a solution of sodium hydroxide and water with melted fats or oils. At the most basic level, soap is the result of a chemical reaction—or, “saponification”—between some kind of fat and alkali (the base). The most commonly used fats are animal- or plant oil-based, whereas sodium hydroxide (lye or caustic soda) is typically used for the base. If you use natural fatty acids (fats and oils), glycerin will be your byproduct; if your fats are industrially produced, the byproduct will be water. Because water is considerably easier to separate from the final product than the glycerin, natural fatty acids are the most common choice. For saponification to occur successfully, you simply stir the elements together continuously until soap forms.

The very first soaps were made by combining wood or plant ashes with animal fats. Ash (which contains potassium carbonate) was gathered in barrels whose bottoms had been layered with stones or sand. The barrels were intentionally left out in the rain so that the ashes would get soaked with water. Once it filtered though the sand, the water was gathered and mixed in a cauldron with animal fats over a fire. As it turns out, the water that percolated through the ashes had collected enough potassium carbonate to start the saponification process and, with that, the basic elements of the soap making process were already in place nearly one thousand years ago. Of course, this initially simple process has been complicated and adapted over time in order to obtain more refined cleansers.

Today there are two typical methods for producing soap on an industrial scale: the boiling process and the continuous process. The boiling process is conducted in a series of steps in order to obtain so-called “neat soap”. It is a very lengthy process that can last from four to eleven days. Natural fats and oils are used and the saponification takes place in large cauldrons called kettles. Caustic soda and the fats are boiled and subsequently treated with brine inside the kettles. The solution separates into an upper layer of “impure” soap and a lower layer of a water/glycerin solution called “spent lye” that gets extracted from the pan to be subsequently treated to recover the desirable glycerin. The impure soap is treated again with caustic soda and is washed to remove the free alkali. Finally the mass is boiled and water is added gradually until it separates again into an upper layer of “neat soap” and a lower level called “nigre” that contains the impurities. After milling and the addition of perfumes and additional fats or oils (so called superfatting agents), neat soap is gathered and composed into the bars that we are familiar with today.

The continuous method, the other industrial method for producing soap, is characterized by the use of fatty acids that are already free of impurities. In this technique, the natural fats were previously separated into purified fatty acids and glycerin. The fatty acids get neutralized with caustic soda to obtain neat soap. This process is much faster than the boiling process—it can take as little as a few hours to complete—and is a favored technique for large-scale production houses.