We've taken a look at the basics of soap chemistry so far. Now let's look at how the components actually combine to make soap.
First, let's take a look at the general chemical structure of an oil. For our purposes, we will assume that we are only using olive oil to make our soap. While most soap makers use a mixture, we will simplify things a bit to make things easier for our example.
Each "R" on this diagram represents an alkyl group, or a batch of carbon and hydrogen molecules. The number of carbons and hydrogens can vary, since there are different regions that grow olives under different conditions. For our purposes, the above diagram will hopefully simply things a bit. We consider our oils to be the "acid" in our saponification reaction. This sounds strange, but most oils are comprised of various fatty acids. These acids are very mild!
Our lye solution, by contrast, is a very strong base. If you remember your high school chemistry class, acids and bases react to produce a salt. In this case, the salt is actually our finished soap. A by-product of this reaction is glycerol, or glycerin. Many commercially produced soaps have the glycerin removed after saponification. Handmade soaps do not, which is part of what makes them much more moisturizing.
Soaps are then left to cure for a period of time. This curing period is vital for a cold process soap, like what we are creating here. It allows any excess water to evaporate from the soap, which results in a harder, longer lasting bar. Typically a soap needs to cure for 4-6 weeks. Some soaps may benefit from a longer curing period, depending on both the recipe and the climate. A soap made in a very dry climate may be fully cured much faster than the same soap made in a very humid environment. Some recipes, such as 100% olive oil, require a much longer curing period, up to one year, before they are considered to be fully cured and ready to use.
Without getting too technical, this is how soap is produced on a molecular level. As more oils are added to the initial mixture, the complexity of the reaction increases. It also helps to impact particular properties of the finished soap. By keeping good notes on each batch, you will be able to find what works best for you, and what you like best about each batch you make. This will greatly help in being able to produce a very consistent bar of soap.