What exactly is a soap? Definitions, explanation, specificities...

The saponification process

Soap is the product of a chemical reaction called saponification.
- It is therefore false to say that soap is natural: soap does not exist "as is" in nature (any more than your grandmother's delicious chocolate mousse!)

Saponification requires the presence of fat (oils, butters, fats...) and a 'base' (as opposed to 'acid' for those who remember their chemistry lessons). It is a total reaction which means that the chemical reaction only ends when one of the two reactants has been totally consumed / exhausted by the reaction
In the saponification process, overgreasing corresponds to the excess fat required to consume all the soda. Overfatting thus ensures that no soda residue remains in the finished product.

In a simple way:

Fat (tryglicerides) + Base (caustic soda or potash) ====> Soap + glycerine

More precisely... the chemical formula of cold saponification with soda

The volumes of Fat and Base necessary for saponification are calculated according to a saponification value.
The saponification number is the amount of potash in mg that must be added to 1g of oil to saponify it completely. This index differs from one fatty substance to another depending on the molar mass of the fatty acids. Soap makers work with calculators to refine these proportions, calculate the rates of overfatting and define precisely the rates of potash or soda to use.

The percentage of glycerine produced by the saponification process is about 8%.

Saponification is an exothermic chemical reaction, which means that it produces heat.

Application of the principle of saponification: types of soap

Depending on the type of base, we obtain either a solid soap (if we use soda) or a soft or liquid soap (if we use potash). We will only deal here with the case of solid soap.

Note Saponification involves the use of soda ash which is corrosive to the skin, eyes and respiratory tract. If it is possible to make soaps at home, it is important to take all the necessary precautionary and safety measures. This article is intended to be informative and does not constitute an instruction manual for home saponification.

Cold saponification

Oils and butters (melted) are mixed with a lye (water + soda) and then blended. When the paste starts to thicken (this is called the trace), ingredients can be added to colour or perfume the soap. The paste is then poured into moulds which are left to rest. The soap blocks are removed from the moulds and cut out, usually the next day. The soaps are then cured (dried).
As seen previously, the chemical reaction of saponification produces heat This is called "cold saponification" because there is no additional heating. At room temperature, saponification is a slow processThis is why the duration of the treatment is at least 4 weeks The cure allows the water to evaporate but also the saponification to finish.

Cold saponification can only be carried out in a traditional way, the rapid setting of the paste and the presence of glycerine do not allow for machine processing or processing in large quantities. The glycerine produced during the saponification process is retained in the soap Only in cold saponified soaps can you get glycerin levels of 7 or 8%.

Industrial soaps

Saponification is not carried out at room temperature but at high temperature. The soap paste is heated to 100/130°C for several hours, days or even weeks (depending on the volume produced) and washed with salt water in order to make the paste more fluid and to eliminate the excess soda and glycerine (which would otherwise stick to the machines). The glycerine carried away by the water is recovered and sold to the cosmetics industry as a moisturizing agent. The soap paste is ground into small pieces (flakes, beads...) called "bondillons".

These bunches are used as a base for soap manufacturers industrial or artisanal
The pellets have no glycerine or grease.
With the help of a plodder or extruder, the pellets are kneaded and enriched, coloured and scented, then cut into bars of soap.
Among the additions we can find dyes, perfumes, glycerine (since it is no longer present in pellets), oils (to obtain an over-greasing) but also sequestering agents (chelating agents) such as EDTA (forbidden in organic farming) which allows the management of hard water by sequestering heavy metals, calcium and limestone .... EDTA is extremely harmful for the environment because it is non-biodegradable and concentrates heavy metals.
BHT (Butylated Hydroxytoluene), a very effective antioxidant, can also be found in the product, allowing it to retain its fragrance, colour and texture; it also stabilizes the over-greasing obtained by adding it. BHT is very controversial; it is suspected of being carcinogenic, endocrine disruptor and can be allergenic
Total additions can rarely exceed 5%.

See an example of the manufacture of pellets and the manufacture from pellets (industrial process) - video

See an example of artisanal manufacture from bondillon - video

Marseille soap and Aleppo soap

The soaps of Marseille and Aleppo are from a hot manufacturing.

Marseille soap does not benefit from an appellation of controlled origin but a specification frames the traditional manufacturing process of traditional Marseille soap. This last one was established by the Union of the Professionals of the Soap of Marseille and defines that the soap of Marseille is

• made from vegetable oils only. Olive oil (or olive pomace), palm oil, palm kernel oil, copra oil (extracted from the coconut)
• without perfume,
• dye-free
• preservative-free
• without additives

The soap paste is washed with salt water, so Marseille soap is free of glycerine and without any grease. Once the saponification is finished, the paste can be "bondillonnée" and shaped into bars for cutting (Savonnerie du Fer à Cheval in Marseille) or poured on the ground (Savonnerie Marius Fabre) before cutting.
There are many adaptations* marseille soap made from poppies, mainly from China and Turkey, to which are added additives, perfumes, colourings etc.
*it is delicate to speak about counterfeits since legally the soap of Marseille is not protected.
The words EXTRA PUR and the Savon de Marseille logo identify traditional Marseille soap.

Other labels, logos or associations of soap makers exist and advocate with more or less rigor or honesty values such as tradition, respect for the environment etc. but work with a lot of dyes, preservatives and other additives (including the very classic EDTA or tetrasodium edta, tetrasodium Etidronate, BHT etc.)

The soap of Aleppo is traditionally made in Aleppo but many soap factories have been destroyed or are no longer in operation due to the situation in Syria. It is composed of olive oil (often second press) and oil of bay laurel which is usually added at the end of the mixture. It retains some of its glycerine (about 6%) and has a variable degree of greasiness, so it can be more or less drying for the skin. It is poured and cut into cubes on the floor. It does not contain any additives, preservatives or colorants.