In recent years, a trend of hand-made soap has gradually become popular. Making soap by hand is a very interesting DIY job. It is moderately difficult but not demanding and is closely related to daily life. Poster girls who like to do it may wish to try it. Regarding the reason why handmade soap is so popular, many people think that, in addition to being good-looking, this kind of "cold soap" made by cold craftsmanship is more beneficial to health than industrially produced soap. For example, it retains many natural beneficial ingredients, is rich in moisturizing factors, is gentler on the skin, etc. Are these claims true?
Whatis soap?
To answer this question, we must first talk about what soap is. Simply put, whether industrial or handmade, soap is the product of a chemical reaction between "oils" and "bases." To be precise, it is the sodium fatty acid produced by the saponification reaction of fatty acid and sodium hydroxide (NaOH, also known as caustic soda or caustic soda, which is a very alkaline substance). With a simple reaction formula, it can be expressed as: fatty acid triglyceride + sodium hydroxide fatty acid sodium + glycerol.
The fatty acids mentioned here are actually a big category, or at least they can be divided into two categories: saturated fatty acids and unsaturated fatty acids.
It is the sodium fatty acid that washes away the stains in the soap. Therefore, the quality of fatty acid sodium is directly related to the decontamination ability of soap. In actual production, the formula of soap (soap) is often very complicated, and the raw materials used are a mixture of several or even a dozen fatty acids, in order to obtain a better decontamination effect and skin contact feeling.
What is the difference between "cold process soap" and "industrial soap"?
So, since they have all undergone the same saponification reaction, what is the difference between handmade cold soap and industrial soap? Let's take a look at the typical preparation method of handmade cold-process soap: first weigh out a certain amount of base oil.
(i.e. fatty acid ester), sodium hydroxide, and water; then sodium hydroxide is slowly dissolved in water and evenly stirred; after the base oil is heated to 60 °C, it is slowly poured into the aqueous solution of sodium hydroxide, poured sideways.Stir continuously and stir for 15-20 minutes after pouring, and maintain the temperature between 40° and 50° C during the entire stirring process. Then, pour the paste into the mold to cool naturally, and place it in a cool and ventilated place. It can be demolded for use after 4-6 weeks.
The typical basic process of industrial soap manufacturing is to add fatty acid ester and aqueous sodium hydroxide solution to the reaction kettle, heat it with steam until the water boils, and stir it vigorously for tens of minutes to an hour. After washing with salt water, layering, drying, and cooling, the soap base (i.e., fragmented soap) is obtained. After the soap base is dried, tabled, and melted, spices and other ingredients (such as disinfectants, moisturizing agents, etc.) are added. Then pour into the mold, demould, and polish to get soap.
Compared to the two processes, it is not difficult to see that the biggest difference lies in the temperature of the saponification reaction: handmade soap is below 60 °C, while industrial soap is often around 90–105 °C. The difference in temperature directly affects the reaction rate. For most chemical reactions, the higher the temperature, the faster the reaction. Roughly speaking, for every 10 °C increase in temperature, the reaction rate roughly doubles. In other words, in the process of handmade soap making, the entire reaction speed is very slow, and the saponification reaction cannot be completed within twenty or thirty minutes, while the industrial soap making process can ensure that most of the raw materials are converted into products.
Another factor that affects the reaction rate is the homogeneity of the reactants. It is not difficult to understand that the oil and water poured into the beaker are generally divided into upper and lower layers, which is called a "heterogeneous phase" in chemistry. If these two substances are to be fully contacted and react, it is necessary to vigorously stir. Obviously, stirring with a glass rod by hand is not as efficient as stirring with a mechanical stirring paddle driven by a motor in industrial soap making; an electric drill will work better as a stirrer, but at low temperatures, the reactants will remain in suspension.The viscosity is large (paste), and its stirring effect is still not comparable to that of the reaction kettle.
So what does it mean to be slow to respond?
This means that, compared with industrial soap, the handmade soap that solidifies after pouring into the mold has not yet reacted completely, and still contains a lot of raw materials that have not yet reacted, including the "base oil" and sodium hydroxide you put in. Sodium hydroxide is a very alkaline substance, and it will quickly cause irritation and chemical burns after contact with human skin, and will cause severe pain after contact with the eyes. In order to avoid such terrible consequences, all handmade cold soaps will refer to "standing for several weeks to mature", which means that the residual raw materials continue to undergo the unfinished saponification reaction at room temperature.
Unfortunately, as mentioned earlier, handmade soaps "in place" do not react as fully as one would like because the saponification reaction is slower at room temperature than at 50 °C. To make matters worse, the soap has solidified into a solid now, and the contact area between the oil and the sodium hydroxide is much smaller than in the liquid state, further reducing the rate of the reaction. Therefore, even after several weeks, a small amount of sodium hydroxide may remain unreacted in the soap. How can it be milder than industrial soap to wash your face with this kind of soap containing strong alkaline substances?
In addition, there is a process of washing with salt water during industrial soap making, the purpose of which is to wash off the unreacted sodium hydroxide, at least most of it; and drying the soap base with hot air also helps to reduce industrial production. strong alkali residues in soap.
It is worth mentioning that there is a kind of handmade soap called "super-fat soap." That is, increase the amount of grease when feeding, or reduce the amount of sodium hydroxide, hoping that the alkali will be consumed and the residue will be reduced. However, this approach does not speed up the saponification reaction; it only completes it when the reaction is finally completed (note that the reaction is completely completed) to ensure that the fatty acid ester and not the base are not reacted. After the soap solidifies for a long period of time, Over time (i.e., waiting for the soap to "ripen"), there may still be strong bases that can irritate the skin.
As for how long the saponification reaction can be completely completed at room temperature, there is still a lack of experimental data. We can only say that this time may be as long as several months or even years. Due to the characteristics of the handmade soap itself, the storage time cannot be too long. Because the vegetable oil used as the raw material is unsaturated fatty acid, and there are still "unsaturated" double bonds after the soap is formed, it is easy to oxidize and deteriorate after a long time; the glycerin in handmade soap will also deliquesce or even liquefy the surface of the soap by absorbing moisture from the air.
Are handmade soaps more natural and nutritious?
Some online articles emphasize that handmade soap retains glycerin, a by-product of the saponification reaction, and this "pure natural glycerin" is an important substance for skin moisturizing. But consider this: after washing your face with soap, most people will rinse the soap foam with water, which will wash away the glycerin in the foam, making the moisturizing effect ineffective.
Some web articles also say that the high temperature in the process of industrial soap making will destroy some of the natural nutrients added. This problem doesn't actually exist. In industrial soaps, a lot of extra spices, plant extracts, glycerin, and other substances are generally added, but they are not added during the saponification reaction, but during the process of melting the soap base and pouring the mold. The temperature at this moment can be completely controlled at below 60 °C, which is not higher than the temperature of handmade soap. On the contrary, there has always been a large amount of strong alkali in the whole process of manufacturing and maturing of handmade soap. These spices and "natural nutrients" are likely to react and decompose under the action of sodium hydroxide, and the degree of damage will be higher.
All in all, it is not difficult to see from the above introduction that the content of strong alkaline substances in hand-refrigerated soap is often high and cannot be accurately detected, so it may not be a good idea to wash your face. If you must use it to wash your face, it is best to leave it for a while. In addition, if you want to use pH test paper to test the pH of handmade soap, you might as well drill a few more small holes in different parts of the soap, take out the samples, fuse them together, and then test. It will be much more accurate than testing only one place. Of course, the process of making soap by hand can be a lot of fun in itself, and it's okay to do it occasionally.
