Superfat in Soap Making

When I teach my lovely students how to use a soap calculator in my cold process soap making classes, one of the main areas of discussion is around the superfat section of the calculator. It is quite a simple concept, but it can sound daunting to new soap makers.

So, what is exactly is superfat? Superfat is a term that soap makers use that refers to an extra amount of oils and butters that are included in a soap recipe. There are a couple of reasons for doing this and the first is to ensure that the soap you make is gentle and moisturising, and the second reason is to ensure that no lye survives in the final bar of soap.

In the chemical reaction that creates soap, the lye is neutralised by the oils and if you used the exact amount to neutralise the lye, in other words zero superfat, then the soap may turn out with too much lye which is also known as lye heavy. So, including a superfat is a safety net to ensure that this does not happen, and it creates a mild soap.

The oils and butters that are not turned into soap by the sodium hydroxide or lye are known as free oils because they have not been saponified.

A question that I get asked frequently is about which oils are the free oils in a recipe that has a superfat percentage? This is difficult to answer because it is unknown, and you cannot do anything to influence the process. But it is most likely that a portion of the slowest saponifying oils, which are the liquid oils such as olive oil or sunflower oil, that will be the free oils.

Soap makers used to add extra oils at the trace stage to superfat thinking that they would not react with the lye, but this does not guarantee that some of the oil will remain unsaponified. And it should be noted that saponification can take 24 to 48 hours to complete.

Now most soap makers account for the superfat in the recipe calculator which makes life so much easier as you only need to select the percentage and it will be calculated for you.

What is a good superfat percentage? This can depend on the oils and butters that you are including in your recipe. I have always used a superfat of 5% and this has worked well in my recipes creating a balanced soap. A good superfat range is between 1% and 8% and I would advise not going over 8% in your recipe because too many free oils will create a very soft bar of soap and could eventually lead to your soap going rancid.

You might also see superfat being referred to as lye discount. Both terms are used interchangeably, and they mean the same thing. If you increase the superfat percentage in a soap calculator you will see the amount of lye decrease accordingly.

For example, a simple recipe using 500g of olive oil with a superfat of 5% will calculate 64g of lye and if this is increased to a superfat of 8% the amount of lye decreases to 62g because the higher superfat percentage will discount the lye further.

I hope this helps you get to grips with superfat in soap making and if you would like to join me in one of my soap making workshops please click the button below to find out more.