What is Superfatting in Soapmaking?

If you are new to cold-process soap making, you have likely come across the term "superfatting." You may have seen recipes that specify a superfat percentage of 5%, 7%, 8%, or even 10%. But what does this percentage actually mean? Does a higher superfat percentage automatically result in a milder soap? And how does it relate to the amount of caustic soda (lye) used? Discover everything you need to know about superfatting, step by step.

What is superfatting?

"Superfatting" refers to the intentional reduction of the amount of caustic soda used in a recipe, ensuring that a portion of the fats and oils remains unsaponified. During the saponification process, oils and butters react with caustic soda (NaOH) to produce soap and glycerin.

By choosing a specific superfatting percentage, you are essentially instructing your soap calculator to use slightly less caustic soda than the theoretical amount required to saponify 100% of the fats and oils.

For example :

• 0% superfatting: the amount of lye required to saponify 100% of the fats is used.

• 5% superfatting: the amount of lye is reduced so as to saponify approximately 95% of the fats.

• 8% superfatting: the amount of lye is further reduced so as to saponify approximately 92% of the fats.

• 10% superfatting: the amount of lye is reduced so as to saponify approximately 90% of the fats.

The key word here is "reduction." One should not assume that a soap with an 8% superfat content contains exactly 8% of a specific oil that has remained intact. The chemical reality is more complex, as all the oils are modified to some degree.

Why use superfatting?

One of the main reasons is to formulate a soap that is less detergent-like and potentially more comfortable for the skin. Soap is naturally capable of removing the fatty substances present on the skin's surface, which is precisely what enables it to clean. "Superfatting" (adding an excess of fat) slightly reduces the amount of lye available for saponification, which can help result in a soap that is less harsh during use. It can also influence the feeling of dryness that soap may leave on the skin.

However, superfatting should not be thought of as simply adding a specific percentage of "moisturizing oil" to the soap. For instance, a soap with an 8% superfat level does not mean that 8% of the finished soap consists of free, unsaponified oil. The actual composition of the soap depends on:

• the oils used

• their fatty acid profile

• the amount of caustic soda

• the amount of water

• the manufacturing conditions

• the curing time

What is the connection between superfatting and lye?

This is one of the most important points to understand when starting out. The "superfat" level (the percentage of unsaponified oil) directly affects the amount of caustic soda used in a recipe. Every oil has a specific saponification value, known as the saponification index or "SAP value", which is used to determine, approximately, the amount of caustic soda required to saponify a given quantity of that oil.

Suppose a calculator indicates that a recipe requires a specific amount of caustic soda for a superfat level of 0%. If you choose a superfat level of 5%, the calculator will reduce the amount of caustic soda. If you increase it to 8%, the amount of caustic soda is reduced slightly further; at 10%, it is reduced even more. This is why you should never alter the amount of caustic soda arbitrarily. Whenever you change the superfat level, the amount of caustic soda must be recalculated.

What happens with a very low superfatting level?

A low level of superfatting means that a greater amount of lye is available to react with the fats. Consequently, the soap may have stronger cleansing power and leave a "cleaner" sensation after washing. For some individuals, particularly those with naturally dry skin or those who wash frequently, a soap with very little superfatting may feel less comfortable. This does not mean that a low level of superfatting is inherently bad; rather, some soaps are intentionally formulated with a low superfatting level to serve a specific purpose. The key is to understand why you are choosing a particular level of superfatting.

And what if the superfatting level is very high?

One might easily assume that "the higher the superfatting, the gentler the soap." However, it is not quite that simple; a very high superfat level can result in a soap that feels overly rich or greasy. It can also diminish the soap's cleansing ability and, in certain formulations, increase the risk of oil oxidation. This may lead to the appearance of what soapmakers call "orange spots", discolorations that indicate the oils in the soap have gone rancid. In short, a higher superfat level does not necessarily mean a better soap. It is best to choose a percentage that is appropriate for the specific goals of your formulation.

What superfatting percentage should you choose when starting out?

There is no single perfect percentage that applies to all soaps. For a daily-use body soap, many soapmakers work with a superfatting level of 5% to 8%.

Here are a few guidelines:

The ideal superfatting level depends on the combination of oils, the intended use of the soap, and the desired characteristics.

Does superfatting make soap moisturizing?

This is a very common point of confusion for beginners. Soap is, first and foremost, a cleansing product that is meant to be rinsed off; it is not a moisturizing cream designed to remain on the skin. A higher level of "superfatting" (the addition of extra oils or fats) may help make the cleansing process less harsh or alter how dry the skin feels afterward, but it does not transform soap into a moisturizing product. The overall formulation is far more significant than the superfatting percentage alone. For instance, two soaps might both have an 8% superfat content yet feel completely different on the skin, simply because they contain different proportions of various oils. Superfatting is just one of many factors that go into a formulation.

Superfatting and lye concentration (be careful not to confuse them)

These two percentages appear in soap calculators and can easily be confused. Yet, they refer to two completely different things.

Superfatting

Superfatting involves reducing the amount of caustic soda relative to the theoretical quantity required to saponify all the fats and oils.

The concentration of caustic soda

The concentration of caustic soda refers to the proportion of NaOH relative to water in the lye solution.

For example, a 30% caustic soda concentration means that the solution contains:

• 30% caustic soda (NaOH)

• 70% water

Adjusting the lye concentration primarily changes the amount of water in the recipe, whereas adjusting the superfat level reduces the amount of lye. Keeping this distinction in mind will be a huge help when you begin calculating your own recipes.

Why is superfatting not such a simple science?

One might be tempted to think: "I chose an 8% superfatting level, so exactly 8% of my oils will remain in the form of oil." But that is not what happens. Each oil has its own unique fatty acid profile. During saponification, these various fatty acids react with the lye to form different soaps. The final soap is, therefore, a complex mixture comprising:

• various soap molecules

• glycerin

• water

• unsaponifiable substances

• possibly some unsaponified fats

• other components naturally present in the oils

The superfatting percentage is therefore a formulation parameter used to calculate the amount of lye, rather than a guarantee that a specific percentage of oil will remain intact.

A simple way to remember the principle

Think of superfatting as a reduction in lye.

Higher superfat = less lye

Lower superfat = more lye

And most importantly: Superfatting does not determine the amount of water. The water quantity is determined separately, based on the lye concentration or the water-to-lye ratio used in the recipe.

In summary

Superfatting is one of the fundamental concepts to grasp when learning about cold-process soapmaking. It involves formulating a soap with less lye than the amount required to saponify 100% of the oils. For many body soaps, a superfat level of 5 to 8% is an excellent starting point. However, the best choice always depends on your specific, complete formulation. Once you understand superfatting, you have a better foundation for understanding:

• lye calculations

• choice of oils

• cleansing power

• soap hardness

• lather

• conditioning properties

• and the overall balance of a recipe

And above all, remember this: never simply copy the amount of lye from another recipe. And if you change the oils, the quantities, the superfatting, or any other parameters, always recalculate the recipe.