Students often ask me about superfatting. It seems to be a confusing topic, so let me simplify this for you.
What is Superfatting?
When you make cold process soap you use a formula to work out how much lye you need to convert your oils and butters to soap. This calculation is based on the saponification value of each of your oils, which is the amount of milligrams of lye it takes to turn 1 gram of that oil or butter into 1 gram of soap. If you use this exact amount of lye to make your soap, all the fats will be converted to soap, which is a 0% superfat. However, if you want to add moisturising qualities to your soap, you can leave some of the fats free in your soap, not converted to soap. These fats will add skin nourishing and moisturising qualities to your bar. This is called superfatting. You can superfat anywhere from 1-20%
How Superfatting is Calculated
The way this is calculated in a recipe is that the calculator works out the total amount of lye you need for all the fats and then it discounts, or reduces the amount of lye in the recipe. So basically, superfatting, is lye discounting. A 5% superfat is a 5% lye discount. A 10% superfat is a 10% lye discount. The easiest way to calculate the superfat is to use a lye calculator, which will work it out for you. You can find my lye calculator here;
How Much to Superfat
How much should you superfat? Well, this depends on the type and quantity of fats in your soap. Superfatting can result in a softer bar with reduced lather. I usually superfat at 5% because it adds richness to the bar without making it too soft or preventing lather. If you add sodium lactate or salt yo your recipe, at 1 teaspoon per pound or 450g oils, that will help to give you a hard bar, even with a superfat.
Coconut oil is an oil which is harsh and drying on the skin if used in high quantities, even though it has great moisturising qualities. Because it is a hard oil, it can be used at 100% in a recipe. However, if you choose to do this, I would recommend doing a superfat of 20%, so that you leave some oil in the bar to nourish the skin. Because coconut oil creates a hard bar, you don’t have to worry about your bar being soft with the extra oil in it.
Superfatting is a personal choice. Some soap makers use up to 15% superfat. The amount will also depend on the recipe. If you have good lathering oils, or a high proportion of coconut oil, you may choose a higher percentage. I would recommend experimenting with different percentages of superfat to find out what you like best. Remember to keep notes with your recipes, as to how your soap came out.