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The Science of Soap Making

The Science of Soap Making

Soap making involves science and art. Whereas art is the fun and exciting part of making soap, it seems that many people feel apprehensive when they see or hear the ‘S’ word (science). Don’t worry you don’t need to be a scientist to make soap! 

On my soap making course when I mention the word chemistry, some of my students look at me with panic on their face. Chemistry is not the daunting subject that many of us experienced at school - imagine how much more fun chemistry would have been if making soap was one of your school projects? 

What is the Science of Soap Making?

Well it’s not that complicated. Soap is formed by combining oils with lye. This process is called saponification.

Triglycerides, which are the main constituents of oils, are converted into soap. In the traditional soap making process, triglycerides are treated with a strong base which is the lye. This releases fatty acid salts (soap) and glycerol (also called glycerine). Glycerine is often extracted from commercial soap to make the bars harder, but all the glycerine goodness is left in handmade soap and it is naturally moisturising.

Contrary to many myths and legends soap cannot be made without lye. The lye is what turns the oils into soap. Without lye there would be no chemical reaction and you wouldn’t get soap at all. Instead you would just create an oily mess.  

What is Lye?

Lye is also known as sodium hydroxide (NaOH). Lye is a strong alkali which dissolves in water. Lye was traditionally made by leaching ashes from hardwood trees but today it is commercially produced.

You can make your own lye from burning wood on a fire and then collecting the ashes. It is a fairly easy process – mix ash with water, allow time for the reaction, filter the mixture, collect the lye – but one that you should do outdoors.

If you are interested in making your own lye check out the process here

What is a Saponification Value?

Every oil has a saponification (SAP) value and you will usually find a saponification chart in a soap making book listing oils and their corresponding values. The value is the number you need to calculate how much lye will turn your chosen oil into soap. Let’s look at olive oil as an example which has a SAP value of 0.134. If you want to make a batch of soap with 500g of olive oil, then you would need 67g of lye (500 x 0.134 is the calculation based on zero superfat). You can of course use a soap making calculator to make life easier.

What is Soap?

Soap is actually a salt of a fatty acid. For example, if you make soap with olive oil the soap that you produce is a salt of the fatty acids. If you consider olive oil as an ingredient in a bar of soap you will see it listed on the ingredients label as sodium olivate which is the saponified version of olive oil.


So, there you have the science of soap making. I am sure you will agree that it’s not that complicated. And I hope you are as fascinated by the process as I am. If you want to learn how to make soap with me why not join one of my natural soap making classes. Click here for more information.