Why knowing your fatty acids makes formulating and soap making so much easier?

In my soap making classes I generally cover a little of the science behind soap making as it is important that you have an understanding of what you are doing and why, so that you avoid making mistakes by doing something that is a big no no in the soap world - switching oils around without running them through a soap calculator is a prime example of this. I don't, however, go in to the in's and outs of fatty acids and how they impact on your soap recipe, but at the time of writing this it is British Science Week 2022 so what better time to up the ante on soap science.

In a nut shell there are 8 fatty acid profiles that form the building blocks of our soap.

4 are saturated and these are usually fats that are solid at room temperature. They tend to reach trace faster and also saponify faster. They are short and medium chain fatty acids. Short chain fatty acids lather up the fastest

4 are unsaturated and they are generally liquid oils. They take longer to trace, longer to saponify and are long chain fatty acids. 

Bear with me on this - all will become clear(er).

The saturated fatty acids are

Lauric  derived from coconut oils and palm kernel oil, can be drying , contributes to big bubbles PH 10.1 Short chain

Myristic again,  coconut oil and palm kernel oils, contributes to hardness, cleansing and lather PH 10.4 Short chain

Palmitic - hard bar, lovely stable lather. Found in palm oil but also lots of animal fats and cocoa butter which is why too much cocoa butter can give you a brittle bar of soap PH10.7 Medium chain

Stearic - hardness and stability of lather, all butters, ie  Kokum, mango, cocoa and and shea butters, also palm oil and tallow - can contribute to stearic spots PH11.4 Medium chain

The unsaturated fatty acids are

Oleic acid - moisturising and conditioning. The most well known is olive oil but also high oleic sunflower oil and canola oil PH 11.2

Linoleic - conditioning and moisturising , not found in the more usual soap making oils, is found in hemp oil PH 10.9

Linolenic - conditioning and moisturising , found in hemp oil and in other more unusual oils for soap making, small amounts in olive oil , sunflower oil and canola oil PH 10.4

Ricinoleic - adds stability to your lather , conditioning and moisturising, only found in caster oil but in a super high level. A little goes a long way. There is no substitute for caster oil in soap making. A blend containing caster oil will lather faster than an identical blend without it. PH 7.4

The first 3 of these do have similar properties in some respects but each individual oil will have varying degrees and will also include some saturated fats, therefore will bring different things to your soap. They also have very different price points and shelf lives which you will need to take in to account.

 How can you use fatty acids to your advantage in soap making?

You now know the 8 types of fatty acids in your soap making butters and oils and how they influence the properties of your finished soap. This means you can look at the make up of a chosen butter or oil and understand the impact it will have on your finished soap and also understand why you cannot swap ingredients and expect to have a similar soap. Let us take sweet almond oil as an example - it is a liquid oil so will be unsaturated. A quick Google search for the fatty acid profile tells me this.

SWEET ALMOND OIL

Oleic acid 62.0 - 86.0 %

Linoleic acid 7.0 - 30.0 %

Palmitic acid 4.0 - 9.0 %

Stearic acid Max. 3 %

So Sweet Almond Oil is very high in Oleic acid, right up there with Olive Oil, in fact it shares many similarities but it is likely to have a lower % of Palmitic Acid which means it may make a slightly softer bar. But you could switch some Sweet Almond Oil for Olive Oil and maintain similar properties in your soap,

OLIVE OIL

Oleic acid 56 - 85 %

Linoleic acid 3.5 - 20 %

Palmitic acid 7.5 - 20 %

Stearic acid 0.5 - 5 %

Let us consider my standard olive oil, coconut oil, cocoa butter recipe. The top image below shows the properties as it stands. I decided I would like to help stabilise my lather and boost the conditioning properties so I added caster oil which does all of those and also avocado oil which is a soft oil, so unsaturated which means it will fall in to the conditioning and moisturising section with either oleic,  but it also has 23.6% palmitic acid so will help with my nice hard bar of soap too. I reduced both my olive oil and coconut oil to see how that would look.

The bottom image is the result.

You can see that my bar is not quite as hard, it has lower Lauric and Myristic figures but Palmitic is the same . My Oleic and Linoleic are virtually the same but my Ricinoleic caster oil boosts my conditioning and bubbly properties. Reducing my coconut oil means that my soap is less cleansing but also potentially less drying. This looks like a nice bar of soap.

Now lets shake things up completely and change my cocoa butter for mango butter. Mango butter is higher in oleic acid so should make for a more moisturising bar of soap but it is also higher in stearic acid which gives hardness.

The reality is that yes , I gain slightly in the conditioning but I lose on the hardness, probably because cocoa butter has a higher level of palmitic acid. In this scenario I would stick with the cocoa butter. 

My intention here is not to drown you in science but to introduce you to the idea that you can get a feel for your bar of soap before you even make it. And if you were toying with the idea of adding something a little different in to your soap you can check the fatty acid profile and just get an idea of how it will impact on your recipe. Unfortunately soap making being what it is, sometimes the reality is not what you were expecting and a little trial and error is to be expected.

I do have some takeaways from this for you however. 

Don't get too hung up on the figures. Consider ingredients that are reasonably priced and accessible for you and then look at formulations.

If you are looking to sell your soap then your target market will impact on your chosen ingredients. What is on the label is just as important as how it feels in the shower, maybe even more so for some groups.

Be brave - try something different. You might have a recipe that is a little high on the cleansing aspect and are concerned it will be too drying but you love the ingredients - up the superfat a little, that may just make it perfect for you. 

Have fun, experiment and let me know how you get on.