Soap and lye
The best thing about handcrafted soaps is that, for the most part, they are almost entirely, if not entirely, natural. Also, handcrafted soaps, made with fats, either vegetable or animal, are real soap. Although many cleansing products today are sold as soap, most are chemical detergents. Those seeking handcrafted soap do so because of its natural nature, which is why some may run for the hills when they find out soap is made with lye.
What is lye?
Lye is a very caustic chemical that was originally obtained via natural means by mixing wood ashes and water. Nowadays, this chemical is manufactured and has a variety of uses, from cleaning ovens, to curing foods, to making soap.
We will be talking about NaOH. It is a chemical compound held together by electrostatic attraction.
Is lye really necessary in soap making?
The bottom line is that without lye, there is no soap. You cannot make soap without lye. Yes, I’ve seen those do it yourself soaps that say you don’t need lye. These are mostly “melt and pour soaps” or grated soaps intended for re-batching. Although YOU may not be making them with lye, they are made with lye when they are manufactured.
Water is polar, meaning that it has a slight charge on both ends. The oxygen part is slightly negative, while each hydrogen is slightly positive. So, the negative O- part of the water will be attracted to something positive, and the H part will be attracted to something negative. Water molecules stick to themselves via hydrogen bonding. The O’s are attracted to the H’s in the adjacent H2O molecules.
When you dunk some oil in water, the water stays attracted to itself via hydrogen bonding and the oil just floats on its own because fat is a neutral molecule.
If you try to wash the slightly greasy dirt on your skin with plain water, not much happens. The water passes over it. The grease is unaffected. You are still dirty. You need something that will take the grease and dirt off of your skin. You need a surfactant.
A fatty acid (in this case we will be using a triglyceride) molecule is non-polar. A fatty acid consists of a triglyceride and glycerol (also known as glycerin) molecule bound together. A triglyceride is an acid, a glycerol is an alcohol, and they are bound together by an ester bond. An ester bond simply means that an acid connects to an alcohol via the removal of water. So, when the triglyceride and the glycerol come together, water is released. The fat molecule is neutral. It has no charge.
Sodium hydroxide, NaOH, consists of an Na positive sodium cation, and on OH- negative hydroxide anion. It is considered a strong base because it completely dissociates in water leaving the Na and the OH- to float free in solution.
The free floating OH- anions break apart the triglyceride molecule by cleaving the triglyceride and the glycerol molecules that were held together by the ester bond. The OH- binds to the glycerol molecule and one of the ends of the free floating triglyceride molecule now becomes negatively charged, this attracts the free floating Na cation. When the cation and the fat come together they form a salt…soap!
No more lyes
Once the lye, NaOH, is used up by the lipid, it no longer exists as lye. The lye is gone. Properly made, finished soap does not contain lye. However, soap in which the lye has used up all of the fat can be pretty harsh on the skin. It is customary for handcrafted soap makers to add extra fat in their recipes. Not only is a soap with extra fat gentler on the skin, it also assures there lye isn't left behind. Many handcrafted soap makers leave in 5% extra fat and some can leave up to 15% extra fat. It all depends on the desired results.