Under a strange name, it is simply the only soap manufacturing technique that allows to preserve all the properties of the raw materials used while ensuring an eco-friendly manufacturing process.
Cold saponification is a process that is very difficult to industrialize. It requires raw materials of excellent quality (nothing can be hidden in a cold process soap) and a long, long time. It takes an average of 5 to 6 weeks for the soap to be usable. The soaps made with this method are by principle artisanal. There is also a cold process soap charter to determine the essentials of the method and to offer a common framework to soap makers.
In the soap industry, when soap is produced in large quantities, hot saponification is used. In principle, manufacturers heat the soap paste up to 120°C in order to accelerate the chemical reaction, which is normally quite slow. The soap paste often comes from "bondillons" (soap noodles : a kind of small rolls of soap made under heat) which are remelted and reshaped in plodders. Yes, that's what it's called!
Soaps and/or soap noodles are often made from palm oil, sometimes from animal fats or from the bottom of vegetable oils tanks, to which many synthetic additives can be added: EDTA, propylene glycol, sodium laureth sulfate, chelating agents… Also, the soap is often separated from its glycerin. In the end, the epidermis can be dried out, even sensitized by the additives.
And to make a long story short, we will avoid talking about shower gel, what it is and what it really does…
On the contrary, cold saponification is an artisanal method which allows to produce solid or liquid soaps rich in vegetable glycerin.
ecause at the beginning, soap is quite simple: it is the mixture of a fatty substance (vegetable oils for example) and an alkaline agent (soda or potash). This gives, in chemistry, soap and vegetable glycerin. With this traditional method, the soap paste is not heated, which preserves the properties of vegetable oils. It also allows the introduction of essential oils (sensitive to heat), mineral or vegetable pigments, and active ingredients such as honey or milk.
As the soap paste is not heated, the saponification process follows its natural rhythm. It lasts at least 4 weeks, most often 6 weeks. The soaps are then in a "curing" phase, which is similar to the maturing time of good cheeses. A cold process soap is often "surgras", which means that a quantity of vegetable oil has been introduced in excess. At the end of the reaction, this excess remains in suspension in the soap, giving it nourishing and antioxidant qualities. The glycerin that forms naturally during the saponification reaction is retained in the cold process soap and moisturizes the skin.
Be careful! Hot saponified soaps can also be very good soaps. This is the case of "real" soaps from Aleppo or Marseille. But they must be elaborated with quality oils, without chemical intervention and following longer processes than industrial soaps.