Superfatting in Soap

Let's get down for some soapy science. Even if you're not a soap maker, 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 and body washes.

soap bubbles

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 fatty acids 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 these fatty acids. Resulting in a bar with lather that is moisturizing, kinda like soap with a little bit 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. As an example, for a soap made with Activated Charcoal I may calculate a higher SF % so the extra moisture can balance any drying effects from the charcoal.
Different oils and butters bring different benefits, but what oils are left unchanged as depends on what's used and the soap making technique.

In Cold Process soap making, SF is calculated by a Lye Discount. Meaning you calculate a specific % less Lye than it would take to saponify all the oils in 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 over as SF. 

In Hot Process soap making, you have the ability to add SF a different way. Instead of calculating a Lye Discount, you can take that percentage as an added fat at the end. 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 that point, all the Lye has been used and saponification is complete. So by adding that SF as a last step, you can choose what specific oil or butter you want to be unsaponified. This technique is especially great for working with luxury ingredients.

I 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 soap makers put a little extra into our soaps for a variety of skin benefits.

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