The Soap Making Process

In both the cold-process (CP) and hot-process (HP) soap making, heat is required for a chemical reaction process that takes place;  that chemical process is called saponification.

With the cold-process (CP), soap making takes place at a temperature sufficiently high enough above room temperature, to ensure that the fats and butters being used are kept in a liquid state, and the process requires that the lye and fat are being be kept warm for an extended time after mixing, to ensure that the soap is completely saponified.

Unlike cold-processed soap, hot-processed soap can be used right away because lye and fat saponify faster at the higher temperatures used in hot-process soap making.

The Hot process was used when the purity of lye was unreliable, and can make use of natural lye solutions such as potash. The main benefit of hot processing is that the exact concentration of the lye solution does not need to be known to perform the process with adequate success.

To ensure that the soap is made to react to its completeness; the Cold process requires exact measurement of lye to fat ratios. Early soapers have developed sophisticated saponification charts to ensure that the finished product is mild and skin friendly. These saponification charts can also be of use in hot-process soap making, but are not as necessary as what they are in the cold-process (CP)soap making.

Purification and finishing

The common industrial process of purifying soap involves removal of sodium chloride, sodium hydroxide, and glycerol (Glycerine). These components are removed by boiling the crude soap curds in water and re-precipitating the soap with salt.  After this the water is then removed from the soap.

This was traditionally done on a chill roll which produced the soap flakes commonly used in the 1940s and 1950s. This process was superseded by modern spray dryers and now by vacuum dryers.

The now dry soap (approximately 6-12% moisture) is then compacted into small pellets. These pellets are now ready for soap finishing.  the finishing process converts raw soap pellets into a salable product, usually bars.

Soap pellets are combined with fragrances and other materials and blended to homogeneity in an amalgamator (mixer). The mass is then discharged from the mixer into a refiner which, by means of an auger, forces the soap through a fine wire screen. From the refiner the soap passes over a roller mill (French milling or hard milling) in a manner similar to calendering paper or plastic or to making chocolate liquor. The soap is then passed through one or more additional refiners to further plasticize the soap mass. Immediately before extrusion it passes through a vacuum chamber to remove any entrapped air. It is then extruded into a long log or blank, cut to convenient lengths, passed through a metal detector and then stamped into shape in refrigerated tools. The pressed bars are then packaged in many ways.