If you want to learn how to make your own soap, there are a few terms which are very specific to soap making that you need to first understand fully. These terms are used to describe the way a soap maker decides to handle the recipe he/she is formulating to creating a particular soap.
Superfatting or Lye Discount
Many soap makers choose to superfat their soap, or apply lye discount (it means the same thing). If a recipe calls for X amount of lye to saponify the oils, we will use less of this lye. Why? This way there is a bit of oil left behind which does not have any more lye to saponify. As a result, the soap will be milder and nourishing to the skin. This process is also called "superfatting".
Every oil has a unique saponification value - the SAP value. This value determines the amount of sodium hydroxide necessary to transform the oil into soap. We could technically decide to use this amount of lye, but then there will be absolutely no oil leftover - everything would be turned into soap. We call this a "0%" superfat or lye discount.
However, we want a bit of oil left behind, or better "unsaponified". This does not mean that there will be oil dripping off your soap, but it simply means that the soap will be more moisturising as part of the oil in the recipe would have not bound completely to become soap.
A common superfatting percentage is "5%" but many people also like using higher percentages such as 10% and even 20% superfatting. A higher percentage of superfatting is normally used when you want your soap to be particularly moisturising. However, bear in mind that more unsaponified oil means also a greater risk of the oil spoilage.
An example of a high superfat could be the one of coconut oil soap. If you want to make 100% coconut oil soap, you will need at least a 20% superfatting or else the soap will be way too drying for the skin due to coconut being very cleansing. If you choose to make a 100% coconut oil with 0% superfat, it will make a great washing up soap for dishes!
Sodium Hydroxide is normally formed by small granules or flakes and needs to be dissolved into a liquid in order to form a “lye solution”.
The liquid doesn't necessarily need to be water, but you could also use different liquids such as milks, aloe vera, tea, herbal infusions to name a few.
Since the lye is has the shape of these solid flakes or pearls solid, you always need water or any other suitable liquid, like milk or aloe vera) to be able to dissolve the lye.
The "most common" percentage of water used in soap making to dissolve the lye is a "25% lye solution: 25% lye to 75% water. However, you can choose to apply a "water discount" and take away some of the water from this proportion.
Why would you do that? This will make the lye solution a bit more concentrated, but it will also allow the soap to unmould and cure faster, while saving some water at the same time. Also, keep in mind that every bit of water in your soap will need to evaporate for the soap to become mild and usable (this happens during the curing period). Technically there is no maximum amount of water you could use, but the more water you use, the softer the soap and the longer it will need to cure.
Whatever liquid you are using, remember that lye cannot dissolve itself into a solution smaller than its weight. You can however apply what it’s called a “water discount”. This simply means deducting some water then whatever is called by the “full water” recipe. Full water means that no discount has been applied. This doesn't mean that you cannot add more water to your soap recipe, but it will not be necessary.
Always keep in mind that the more water you add, the more time the lye solution you have used in your soap recipe will take to evaporate, and the longer the soap will take to cure. This is why the soap is considered still caustic when it’s just being unmoulded, and it will become milder and milder the longer it cures. The cure period is 4-6 week, but I find a period of 6 weeks is better, and the soap becomes extra mild after 3-4 months of cure time.
Below are the most common water/lye ratios:
The most common ratio is called “full water”:
Ratio: 1:3 (1 part lye, 3 parts water)
In percentages: Water: 75%, lye: 25%
Mild Water Discount
Another popular water discount is closer to a lot default setting, you will find in online lye calculators.
Ratio: 1:2.5 (1 part lye, 2.5 parts water)
In percentages: Water: 71.4%%, lye: 28.6%
Moderate Water Discount
A moderate water discount is one of the most manageable and flexible if you want to do some designs.
I personally use this across most of my recipes as it allows for a much shorter cure time, and a firmer soap out the mould.
Ratio: 1:2 (1 part lye, 2 parts water)
In percentages: Water: 66.7%, lye: 33.3%
Strong Water Discount
A strong water discount can be applied for different reasons. First of all, you may want to apply a strong water discount if you are adding liquid additives, which will increase the amount of water in your soap. For example, if you are adding fruit of vegetables, which contain water in it, or if you are adding milks at trace. In this case, you can remove the amount of liquid you want to add at trace from your lye solution.
Experienced soap makers who know that their ingredients will not accelerate trace too much and are making a simple, plain soap with no designs may also decided to apply a strong water discount.
Ratio: 1:1.5 (1 part lye, 1.5 parts water)
In percentages: Water: 60%, lye: 40%
Maximum Water Discount
Ratio: 1:1 (1 part lye, 1 parts water)
In percentages: Water: 50%, lye: 50%
What is your favourite superfat or water discount? Do you have any questions? Let me know in the comment below!