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.
The alkalis used for soap making are Sodium Hydroxide (chemical formula: NaOH), and Potassium Hydroxide (chemical formula: KOH).
In their purest form, both NaOH and KOH are solid (prill, powder or flakes). When we talk of “alkali”, we refer to either Sodium or Potassium Hydroxide. This is also referred to as “caustic soda”, – whereas a “caustic solution” or “lye solution” is the strongly alkaline liquid made by dissolving either pure NaOH or KOH in water. The alkali solution used by the soapers is typically referred to as the lye.
In general reacting fat with Sodium Hydroxide (NaOH) will produce a hard soap and when reacting with Potassium Hydroxide (KOH) a softer or liquid soap.
Working with these chemicals should be done under adult supervision at all times. Please note when working with these corrosive chemicals make sure you follow all SAFETY Precautions; ensure that you wear personal safety protection and keep this product away from children.
As a side note it must be stated that the saponification process (soap making) is NOT possible without using either NaOH or KOH. However, a properly formulated and executed natural soap should contains some excess fatty acids (which are beneficial for your skin), plenty of natural glycerine (which, also, is good for your skin), and no free unreacted alkali.
Natural Soap is derived from either oils or fats. Sodium tallowate, which was a common ingredient in many soaps in the past, was in fact derived from rendered beef fat. Soap nowadays is made from pure vegetable oils, such as palm kernel oil or coconut oil, and the end product is typically a slightly softer soap; one of the main products that is been found on todays commercial soap labels is Sodium Palm Kernelate or Sodium Cocoate being made from Palm Kernel oil and Coconut oil respectively.
If soap is made from pure Olive oil it may be called “Castile” soap or Marseille soap. The Castile name is also sometimes applied to soaps with a mixture of oils, which contain a high percentage of oleic fatty acids such as Sunflower oils and to liquid soaps.
The soap making process uses a range of quality oils and butters such as
- Olive,
- Coconut Oil,
- Wheatgerm Oil,
- Castor Oil,
- Shea Butter,
- Hydrogenated Palm Oil.
to list a few.
Each oil as chosen by the soap maker has unique characteristics that provide different qualities to handmade soaps including mildness, lathering and hardness. For example; Olive oil provides mildness in soap; Coconut oil provides lots of lather while Castor and Palm oils provides hardness.
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.
Hot Process
In the hot process method, lye and fat are boiled together at 80 – 100 °C until saponification occurs; some soap-makers claimed that they can determine the end point by taste [certainly not recommended:- they claim that the distinctive and caustic taste of lye disappears once all the lye is saponified]. The saponification progress is also seen by normal observation (the experienced soaper can tell when the gel stage and full saponification have occurred).
After full saponification has occurred, the soap produced via the industrial process is precipitated from the resultant solution by adding salt, and the excess liquid is drained off. The hot, soft soap is then spooned into the mould(s). The experienced home craft soaper here will add the colour and fragrances , and or essential oils before moulding the soaps
A cold-process soap maker first determines the saponification value of the various fats being used on a saponification chart, which is then used to calculate the appropriate amount of lye. Excess un-reacted lye in the soap will result in a very high pH and can burn or irritate skin. Insufficient lye, and the soap results in a greasy and oily product. Most soap makers formulate their recipes with 3-15% excess oil so that all of the lye is reacted and that excess fat is left for skin conditioning benefits. The lye is dissolved in water and the resulting solution mixed with fat. [ Please take great care and use appropriate precautions (apron, goggles, gloves, face-mask) as the resulting liquid product is very corrosive to the eye and skin as well as many other surfaces] Once the resulting solution has cooled to about 25-35 °Celsius, this lye-fat mixture is stirred until “trace”, that is, the two thin, clear substances become cloudy and start to thicken. After much continuous stirring, the mixture turns to the consistency of a thin pudding.
Fragrance oils, essential oils, botanicals, herbs, oatmeal and/or other additives are added at light trace, just as the mixture starts to thicken.
The batch is then poured into molds, kept warm with towels or blankets, and left to continue the saponification process for 18 to 48 hours. During this time, it is normal for the soap to go through a “gel phase” where the opaque soap will turn somewhat transparent for several hours before turning opaque again. The soap will continue to give off heat for many hours after trace.
After the insulation period the soap is firm enough to be removed from the mold and cut into bars. At this time, it is safe to use the soap since saponification is complete. However, cold process soaps are typically cured and hardened on a drying rack for 2-6 weeks (this removes the water that is part of the process) before use.
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.
