The Chemistry of Soap Making from Cosy Cottage

The Chemistry of Soap Making

Have you ever wondered what actually happens when soap is made? The process is far more fascinating and scientific than most people realise. In this post, our founder Clara, a fully trained chemist from Imperial College London and an Associate of the Royal College of Science, walks you through the chemistry behind every bar of Cosy Cottage soap.

You can even experience the process for yourself at one of our Face to Face Soapmaking Workshops in Malton, or try it at home with one of our make-at-home soap making kits.

If you'd like to explore the history of soap making first, take a look at our blog post The History of Soap Making.

What is Saponification?

Soap is the product of a chemical reaction between dissolved, white, alkaline crystals called lye (also known by its chemical name, sodium hydroxide) and triglycerides (the chemical name for oils, waxes and fats). The scientific word for this chemical reaction is saponification.

The diagram below shows the process from start to finish. You'll notice that in addition to soap, glycerin is formed as a by-product of saponification. This is entirely beneficial and glycerin is a colourless, viscous substance that stays within the soap and acts as a humectant (a substance that preserves moisture), making our soap naturally kind to skin.

The Oils and Fats We Use

The oils, waxes and fats used in soap making are similar to what you might find in a kitchen cupboard. Different combinations create different characteristics in the finished soap. At Cosy Cottage, we use coconut oil, extra virgin olive oil, castor oil and sometimes sweet almond oil, among others. Each ingredient is chosen carefully for the properties it brings to the final bar.

Clara's scientific background has been invaluable in developing our formulations. That expertise is behind everything from our best-selling natural deodorant to our best-selling solid shampoo bar.

The Soap Making Process Step by Step

Those who have attended our popular soap making workshops and demonstration days are always amazed and fascinated by the complexity involved in making soap from scratch and delighted to learn the new skills involved. Here is how we do it:

Mixing the Lye

We begin by accurately weighing our lye and mixing it with just enough water to dissolve it. As the lye dissolves, the sodium hydroxide molecules split apart into sodium and hydroxide ions, releasing energy and causing the mixture to heat up. This is known as an exothermic reaction.

Lye is a highly alkaline substance and both the solid and dissolved forms are highly toxic and can cause very serious burns if they come into contact with skin. We always wear gloves, face masks and safety glasses throughout the entire process and we work in a well ventilated location.

Combining the Ingredients

We begin by melting and mixing our oils, waxes and fats in exactly the right quantities. To make soap that is safe to use, different combinations of oils require different quantities of lye and very careful calculation is essential. We then slowly add the hot lye solution to our melted oils, waxes and fats, mixing thoroughly.

Reaching the Point of Trace

After several minutes of vigorous mixing, the mixture becomes thicker and paler as soap and glycerin begin to form. When the mixture reaches the right consistency; traditionally called the point of trace, we add essential oil fragrances and pour it into moulds to set.

The Curing Process — Why It Matters

After 24 hours, the solidified soap is ready to cut into bars. But it isn't ready to use just yet; at this stage it's still very alkaline and would irritate the skin.

The soap needs to cure. During curing, it dries out and becomes progressively less alkaline over a period of around 2–3 weeks. By the end of this process, the soap is much harder and much gentler on the skin. The finished soap remains very slightly alkaline, which helps to discourage the growth of bacteria, fungi and other microorganisms;  great for hygiene, great for skin, and great chemistry.

Try Soap Making for Yourself

Listen to our podcast episode 'How is Soap Made?' for more on the science behind our soaps.

Want to see the chemistry in action? Join us at one of our workshops or try one of our make-at-home packs — it's a wonderful way to learn something new and come away with beautiful, natural soap you've made yourself.

Frequently Asked Questions About Soap Making Chemistry

What does saponification mean?

Saponification is the exothermic chemical reaction that creates soap. It occurs when lye (sodium hydroxide) reacts with oils, waxes and fats (triglycerides) to produce soap and glycerin as a by-product. The word comes from the Latin sapo, meaning soap.

Is lye safe in finished soap?

Yes, completely. Although lye is a caustic substance that must be handled with great care during the soap making process, it is fully consumed by the saponification reaction and converted to soap. There is no lye remaining in a properly made, fully cured bar of soap.

Why does natural soap need to cure?

Freshly made soap is still highly alkaline and would irritate the skin. During the curing period of 2–3 weeks, the soap dries out and its pH drops to a skin-friendly level. Curing also hardens the bar and improves its lather. Skipping this step would result in a soap that is harsh and short-lived.

What is glycerin and why is it in soap?

Glycerin is a natural by-product of saponification. It is a colourless, odourless, viscous liquid that acts as a humectant, meaning it draws moisture from the surroundings to the skin and helps retain it. In many commercial soaps, glycerin is extracted and sold separately. In our handmade soaps, it remains in the bar, which is one of the many reasons natural soap is so much kinder to skin than mass-produced alternatives.

What is the point of trace in soap making?

The point of trace is the stage in soap making when the mixture of lye solution and oils has been mixed sufficiently for saponification to be well underway and sufficiently progressed to continue to completion without further stirring. At this point, the mixture has thickened to a consistency similar to a light custard and a stirrer leaves a visible trace on the surface when drizzled. This is the moment when fragrances and other additives are incorporated before pouring into moulds.

Can I make soap at home?

Yes, with the right safety precautions and equipment. We offer face-to-face soap making workshops in Malton, North Yorkshire where you'll learn the process safely under expert guidance, as well as make-at-home kits with everything you need to get started.