Superfatting in Soap
Let's get down for some Soapy Talk. Even if you're not a Soapmaker, you might want to know about the practice of Superfatting in soap. It's part of what sets handmade artisan soaps apart from commercially made soaps or body washes.
At its most basic level, soap is made with 3 main ingredients- Fats, Sodium hydroxide (also called Lye), and Water to dissolve the Lye. The dissolved Lye interacts with the fatty acids, chemically changing them into soap. During this process, called saponification, all of the Lye is used up as it reacts and transforms your Fats (Oils and Butters) into soap.
Superfat (SF for short) is a percentage of fatty acids that remain unsaponified in a finished soap. This gives you the cleansing properties of soap plus the skin conditioning properties of the unchanged fatty acids, resulting in a bar with lather that is moisturizing, like soap with a percentage of lotion all in one!
All of my soaps are made with a percentage of SF. I sometimes vary the amount depending on the soap's purpose (a facial bar will be different than a body bar, or hand soap) and to balance out other ingredient properties. For example, a soap made with Activated Charcoal, I may calculate a higher SF % so the extra moisture can balance the drying effects of the highly cleansing Charcoal. Different oils and butters bring different benefits, but what oils are left unchanged as SF depends on the types used and the soapmaking technique.
In Cold Process soapmaking, SF is calculated by a Lye Discount. Meaning you calculate a specific % less Lye than it would take to saponify all of your recipe. Calculating SF this way is easy, but it does have one drawback- you have no say in which specific fatty acids the lye reacts with and which are left unchanged. Usually there's a range, and that works well unless you want a specific Oil or Butter to add specific properties as your SF.
In Hot Process soapmaking you have the ability to add SF a different way. Instead of adding it all as a Lye Discount, I like to split the total SF% two ways. A small amount I keep as a Lye Discount in my formulation. The remaining percentage I will apply to a specific Oil or Butter that I want to have as the SF in that soap. During Hot Process, the saponification is sped along by the application of heat and stirring the soap batter as it goes through phases until it has finished the chemical reaction. At this point, all the Lye has been used. So I can add a bit of Butter or Oil and know that it will remain unchanged since there's no Lye left to react with. This technique is especially great for working with luxury ingredients.
I use and love both methods since each way has pros and cons depending on your recipe goals.
So in summary, Superfatting yields Soap + Moisturizing Fatty Acids, and is one of the many ways we soapmakers put a little extra into our soaps for a variety of skin benefits.
If you have any questions about percentage rates, or even which Oils or Butters I SF with, feel free to ask!