Posted on February 21st, by Katie Legere in Uncategorized. No Comments

In honour of my fifth year making soap, let me tell you what I know, the science short & sweet behind hot process soap making!


A natural fat needs to be broken down into its molecular components which are glycerin and fatty acids. This is done by heating fats (oils & butters) in an alkaline solution. This alkaline solution is sodium hydroxide (lye) and distilled water.  The oils & butters react with the alkaline solution to form soap. This process is saponification.  In cold process soap making, scents and colours are added and then poured into molds, the saponification process then takes place over a varying amount of weeks. In hot process soap making, the mixture is heated using the double boiler method to accelerate the saponification process. Once the mixture has saponified, essential oils for scent and/or colour is added and poured into molds, left to cool and harden for 24hrs. The hot process method allows soap to be used directly after the soap has cooled and hardened.

Each oil that is used in free to be soaps has a saponification value (SAP value). This means that a precise weight of an oil is calculated with its SAP value to determine the amount of lye that is required to provoke saponification.

Because many fear the caustic quality of lye, free to be soaps are superfatted with the special oils of hemp seed and avocado to ensure that there is more oil than lye. To have more oil than lye means that the soap will be guaranteed not to be lye-heavy (which can be a skin irritant), and also will enhance the lather and moisturizing quality.

Real, authentic soap requires lye. To make soap without lye is to make the common science volcano experiment using baking soda and vinegar without the vinegar. No vinegar and you’ve just got a pile of baking soda. No lye and you’ve got yourself a pot full of oils and butters.

I give thanks to the pioneers of soap making, a brilliant discovery and a meaningful way for me to be creative in the kitchen while lessening our footprints and reclaiming kindness to our skin.


Fun Fact: I found this book antiquing with my friend, Sarah in Kinmount, ON area.

This book caught my eye in amongst a large barn full of all you can imagine.

This book was written in 1955 and has been a go to resource in my soap making journey!


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