How is soap made… part I: Factory Production

Soap and detergent manufacturing consists of a broad range of processing and packaging operations. The size and complexity of these operations vary from small plants employing a few people to those with several hundred workers. Products range from large-volume types like laundry detergents that are used on a regular basis to lower-volume specialties for less frequent cleaning needs.

Cleaning products come in three principal forms: bars, powders and liquids. Some liquid products are so viscous that they are gels. The first step in manufacturing all three forms is the selection of raw materials. Raw materials are chosen according to many criteria, including their human and environmental safety, cost, compatibility with other ingredients, and the form and performance characteristics of the finished product. While actual production processes may vary from manufacturer to manufacturer, there are steps which are common to all products of a similar form.

Let’s start by looking at bar soap manufacturing and then we’ll review the processes used to make powder and liquid detergents.
Traditional bar soaps are made from fats and oils or their fatty acids which are reacted with inorganic water-soluble bases. The main sources of fats are beef and mutton tallow, while palm, coconut and palm kernel oils are the principal oils used in soapmaking. The raw materials may be pretreated to remove impurities and to achieve the color, odor and performance features desired in the finished bar.

Soap was made by the batch kettle boiling method until shortly after World War II, when continuous processes were developed. Continuous processes are preferred today because of their flexibility, speed and economics.

Both continuous and batch processes produce soap in liquid form, called neat soap, and a valuable by-product, glycerine. The glycerine is recovered by chemical treatment, followed by evaporation and refining. Refined glycerine is an important industrial material used in foods, cosmetics, drugs and many other products.

The next processing step after saponification or neutralization is drying. Vacuum spray drying is used to convert the neat soap into dry soap pellets. The moisture content of the pellets will vary depending on the desired properties of the soap bar.

In the final processing step, the dry soap pellets pass through a bar soap finishing line. The first unit in the line is a mixer, called an amalgamator, in which the soap pellets are blended together with fragrance, colorants and all other ingredients The mixture is then homogenized and refined through rolling mills and refining plodders to achieve thorough blending and a uniform texture . Finally, the mixture is continuously extruded from the plodder, cut into bar-size units and stamped into its final shape in a soap press .

Some of today’s bar soaps are called „combo bars,“ because they get their cleansing action from a combination of soap and synthetic surfactants. Others, called „syndet bars,“ feature surfactants as the main cleansing ingredients. The processing methods for manufacturing the synthetic base materials for these bars are very different from those used in traditional soapmaking. However, with some minor modifications, the finishing line equipment is the same.