Soap making is a very simple chemical process but can be very daunting if you fail to follow some very simple yet crucial principles.
The three main components you must always get right to the decimals are Sodium / Potassium Hydroxide, water (these two makes what we call Lye) and Oils.
Other components are less self-destructive if you vary a few
ounces since most of them are used as fillers (e.g. Sodium Silicate, Kaolin,
Borax etc.) However, these too should not be abused since the more fillers you
add to your soap, the less Total Fatty Matter (TFM) you will have in your soap.
Soap with less TFM is of lower quantity. Therefore, it is
advisable not to use fillers more than 50% of the total weight of the oils.
Lye on the other hand requires a bit more accuracy when making soap. Once you determine the total batch you want to produce, you need to calculate the right amount of Sodium or Potassium Hydroxide (Caustic Soda) that is required to fully saponify all the oils without leaving too much of the Caustic Soda in the Soap.
In other words too little Caustic Soda will not be able to break down all the oils, and it will take too long for the soap to cure. The soap will have traces of un-saponified oil droplets. After a while, these oil droplets will undergo oxidation yielding peroxides.
Too much will burn all of the fat and still remain in the soap. Caustic Soda is basic and can burn or irritate the skin. Excessive use of caustic in your soap will have a very drying effect on your skin and too much could actually cause a chemical burn or blindness since it will have a PH higher than the recommended PH level of 8.5.
In case you didn’t know, the PH of your skin is around 4.5 but is covered with a layer of sebum. Soap with more than 8.5 PH will react with our 4.5 skin PH and deposit a thin layer of soap on your skin hence causing irritation.
My first mistake in soap making was actually with Lye. I was still very new in soap making and anxiety and impatience preceded my caution. I had just learnt a Laundry bar soap formula from my trainer and I was eager to earning some income.
I made a few individual 800g bar soaps and the results were no so bad in my standards then (although the first batch almost solidified in the mixing bowl before I could pour all of the soap into the mould. I took too long stirring and I didn’t realize when the soap traced.
After a few successful bars of soap, I felt now it was time to do a bigger batch. I had just bought a 12-bar mould and I thought, instead of making 800g bars of soap, what if I multiply the quantities of each ingredient by 12 and do a 12-batch of soap all at once!
That was a very expensive mistake that costed me close to $50 of wasted ingredients.
First, let me explain something we call Sap value.
According to Wikipedia, Sap (or Saponification) Value is the number of milligrams of potassium hydroxide (KOH) or sodium hydroxide (NaOH) required to saponify one gram of fat under specific conditions. In simpler terms, Sap value is the amount of Lye required to convert or ‘saponify’ a fat into soap.
Every oil/fat type has its unique Sap value depending on its fatty acid chain length. Oils with a shorter fatty acid chain consumes less caustic soda than those with longer chains.
Luckily, we don’t have to memorize all these values for each soap. The values have already been determined; all you need to do is check the sap value table and calculate the amount of Lye you need based on the weight of that particular oil/fat.
For example, Palm oil has a Sap value of 140. This means for every 1000g of Palm oil, you need 140g of Caustic Soda to fully saponify the oil into soap. Assuming in your soap recipe, the amount of palm oil you intend to use is 261g, the SAP value in this case will be:
SAP = 140g x 261g
1000g
SAP = 36.54
This means, to fully convert 261g of palm oil, you need 36.54g of Sodium Hydroxide.
Back to my expensive mistake.
Instead of calculating the SAP value for my new batch, I simply multiplied the ingredients and the results were disastrous. I ended up adding too much caustic soda into the soap that burned all the oils and there was too much of it left in the soap (you should see the way the mixture was bubbling like a volcano that’s about to erupt!).
In this journey of soap making, never multiply ingredients without confirming the SAP values and MVC (moisture value content).
If you don’t know how to calculate MVC in soap, please watch
my next blog on water – Lye concentration.