What does the term "superfatted" mean?
Type " superfatted soap " in an internet window and you will have a lot of information, both about industrial soaps sold in supermarkets, shops, (para)pharmacies (superfatted breads*) but also industrial soaps sold on local markets which are next to the real soaps of soap makers.
In the name " superfatted soap ", we first have the word soap.
You should know that industrialists who make soap (not detergent but soap; it's already better) generally do so from soap shavings called bondillons, which are themselves industrially manufactured by other companies. These soap pellets no longer contain glycerine! Indeed, the natural glycerine resulting from industrial saponification is sold separately, more profitably, for other cosmetic preparations.
If the market so desires, the industrial soap manufacturer will add natural or synthetic (!) glycerine at the end of the manufacturing process, up to +/- 1% compared to 6 to 7% in artisanal cold saponification.
As for the term " superfatted"... it generally informs the consumer that a vegetable oil or butter has been added to the soap product to improve the hydration, suppleness and protection of the skin. Usually, sweet almond oil, shea butter, are popular with the general public, along with clays and other popular ingredients such as Aloe Vera. In shops, you will also find argan oil, mink oil (yes, you read correctly), ... Unfortunately, if the announcement of these "precious" additions fills an important part of the packaging, they are only found in minute quantities in the soap (sometimes ... less than 1%).
Profit when you've got us!!!
Let's get back to artisanal saponification.
Soap results from the reaction of fatty products with a caustic solution.
A (very) long time ago, animal fat from goats, wild boar, pigs, ... was used and mixed with a solution of water and burnt wood ashes to obtain a "washing paste" that cleaned fabrics better than a simple soaking in the river or at the public washing place.
It wasn't really the time to take a bath, let alone a shower to get clean and smell good, but it was a good start.
Everyone knows the soap of Aleppo. It is a saponification by cooking for 72 hours in huge copper vats, a mixture of olive oil with water and vegetable soda produced by the glasswort. The proportion of bay laurel oil added at the end of preparation determines the level of superfatting of the soap as well as the desired effect on the skin.
In a way, Aleppo soap, a natural product par excellence, is the ancestor of all soaps. But it is a "cooked" soap. And this cooking modifies, even alters, the final properties of the oils used to make the soap.
Cold saponification generally uses vegetable oils or butters, of good quality and if possible organic. The caustic solution is prepared with low mineralized or even demineralized water and pure caustic soda also called sodium hydroxide (NaOH). Potassium hydroxide (KOH) mixed in different proportions with sodium hydroxide (NaOH) is used to make liquid soaps.
The chemical reaction is as follows:
Oils + Caustic solution => soap + glycerine.
That's the simplified and easy version. Let's see it in more detail
Let's talk about "Oils".
To transform a quantity of oil into soap and glycerine requires a quantity of caustic solution that varies according to the oil used. Thus, it takes "on average" 192 grams of pure potassium hydroxide to transform 1000 grams of olive oil into soap and glycerin. It is said that the saponification index of olive oil is 0.192.
If you want to make solid soap, which is usually the case, then you use Sodium Hydroxide. Simply divide the amount of KOH (Potassium Hydroxide) by 1.4025 to obtain the amount of 120.05 grams of NaOH needed for the complete reaction.
The hard part is over. But it remains to be qualified.
Why do we say "on average" and "about" when we are talking about precise calculations with products that are known to be dangerous, such as caustic soda? For a very simple reason: The saponification index of olive oil (0.192) is an average or a generally accepted trend for this oil. In fact, some olive oils will have an index of 0.184 while others can go up to 0.196. This depends on many factors such as the variety or age of the olive trees, the type of soil, the type of crop, the climate, the altitude, the year of harvest, ... and the age of the producer (no, just kidding).
That explains this:
Since the finished product, soap, must be safe and non-caustic to the user's skin, a margin of safety is taken by using more oil than necessary. This is called "soda reduction superfatting".
A few more figures: In practice, an olive oil with a saponification number of 0.184 will only need 184 grams of caustic soda to react completely with the said 1000 grams of oil. On the other hand, 1000 grams of olive oil from another region will require 196 grams of caustic soda. That is a difference in mass of caustic soda of 12 grams.
Using the most frequent value of saponification index, i.e. the index of 0.192 for olive oil in the first case, 43 grams of olive oil will be in excess and will participate in a form of superfatting (about 4.3% of the oil mass). In the second case, there will be too much caustic soda because precisely 21 grams of olive oil will be missing for the reaction to be complete, i.e. 2.1% of the oil mass.
Consequently, a soap maker will always take the precaution of using more oil than necessary to avoid this risk. And there are several ways to solve the problem:
The first solution is to make a soap based on olive oil with a fat content at least higher than the extreme case encountered for this oil. It can thus be stated that any olive oil soap manufactured with a minimum 2.1% superfatting calculation will guarantee a soap at worst neutral (0% superfatting), at best 6.4% superfatting (2.1 + 4.3%). To this it should also be added that the saponification of this kilo of olive oil will generate a non-negligible quantity of nearly 8% of the total mass in glycerin. But although glycerin is excellent for the skin, it is not an oil.
The second solution to compensate for this disparity in the saponification index, the most frequent and for other reasons as well, is that to make a soap with interesting characteristics, a mixture of several oils and butters is usually prepared. Each of these oils and butters has its own saponification number. And statistically, the differences in the different indices will tend to neutralize each other. Thus, if I use an olive oil with a higher saponification index than the index generally used in the calculations, it may eventually be mitigated by an index for shea butter that is lower than the one generally expected.
The third solution is to provide for an additional superfatting, the so-called "second superfatting", to ensure in the worst case that the soap will be well superfatted by excess oil. This superfatting is always done at the end of the preparation, at a moment called "the trace" with a so-called "precious" oil whose benefits for the skin are to be preserved by avoiding as much as possible that it reacts with the caustic soda.
Each artisan soap maker has his own practice but each method guarantees a healthy and quality product.
Let's take a simple example by making a soap based on olive oil, coconut oil and sweet almond oil. The goal is to make a soap that is about 8% superfatted and to benefit as much as possible from the benefits of sweet almond oil.
Thanks to a calculator (Mendrulandia, Soap Calc, ...) or a spreadsheet to free oneself from the internet, we will calculate "precisely" the quantity of caustic soda to obtain a 3% superfatted soap by "soda reduction". As explained above, depending on the variety of olive oil, it will be at worst neutral from 2.1% of superfatting but can reach a 6.4% superfatting by taking the average index of 0.192. The same approach is followed for coconut oil. Here we are certainly on the safe side, so the finished product will not be caustic!
Then, and to finally arrive at a theoretical value of 8% of superfatting, 5% of the initial oil mass will be added as sweet almond oil, i.e. 50 grams of good organic sweet almond oil. This oil will be mixed at the end of the preparation of the paste when an emulsion between the olive oil and the caustic solution has been prepared using a mixer. The sweet almond oil will be blended, not mixed, in the preparation. This added and blended oil will increase the superfatting while preventing it from being deteriorated by the reaction within the emulsion. From a practical point of view, the finished product will therefore be a superfatted soap whose calculated value will be 8% but which will be at worst 5.9% superfatted, of which 5% with sweet almond oil, at best 11.4% superfatted, of which ... 5% with sweet almond oil. Which was finally the goal!
It's a little indigestible, I'll grant you that. But it is, in my humble opinion, useful to know that a product as simple in appearance as a good soap requires a minimum of knowledge and care in its development to provide a quality product, healthy and good for the skin.
And that's the reason why we use a real handmade soap rather than a simple detergent.
In the next topic, I promise you, it will be much simpler: no numbers! Just information about the different characteristics on which the artisanal soap maker can act to produce a soap more or less moisturizing, foaming, creamy, soluble, hard, washing, ... only by the choice of oils and the rate of superfatting. Tailor-made, haute couture, gastronomy, ... made bubbles!
See you soon,
Bruno, Craftsman soap maker
* Bread: a word that doesn't really mean soap but a toilet product that substitutes for it.
KissPlanet offers handmade soaps naturally superfatted: