Stearic Acid

Stearic Acid is a fatty acid that is found in most Oils, however being very high in animal fats and hydrogenated oils.

What is Stearic acid?

Stearic acid is a long chain saturated fatty acid also called Octadecanoic acid CH3(CH2)16COOH it has an 18-carbon chain compared to Palmitic Acid with a 16-carbon chain. Stearic Acid is more abundant in animal fats than vegetable fats (typically <5%). Shea butter and coco butter are an exception with higher levels between (20%-35%) also Hydrogenated soybean oil or Soy Wax typically has anywhere from 70%-85% Stearic acid content. Stearic Acid is very similar to Palmitic Acid since they are both long chain fatty acids however both are very common( being in a multitude of different oils to one degree or another) Stearic Acid is essentially the animal version of Palmitic Acid. Its name comes from the Greek word Stear which means Tallow. Stearic Acid is a hard wax that with a melting point of 157°F(69°C). You can expect around 3-4% Stearic acid in Coconut Oil, 4-6% in Palm Oil, Lard and Tallow 13-20%. In general most soaps have anywhere from 5-20% in total fatty acid content. Usually a lot of natural Soaps use Palm Oil instead of Tallow thus having less stearic and more Palmitic Acid.

What are Stearic Acid’s effect on Soap?

Stearic Acid when used in Soap produces a very hard long-lasting bar with a stable creamy lather. When Lye is added to Stearic Acid it becomes Sodium Stearate or Potassium Stearate which is a very common surfactant used in many comercial soaps and detergents. It is very useful in shaving soap since it creates a thick creamy lather. Shaving Soaps should also use a dual lye solution since the high amounts of long chain fatty acids produces a very hard bar that will have difficulty lathering with a brush. Since Potassium Hydroxide is used in making liquid soaps this will make the bar softer.

The soaps made with large quantities of Stearic acid tend to be very hard and trace very fast so adding extra water and working fast is key to producing a smooth bar of soap. I try not to over mix when I use stearic acid in my soap, just using the stick blender in small burst and stirring with it in between. Personally I think adding Stearic acid to my soaps improves the cure time and the amount of fragrance that lingers in my soap.

How to use Stearic acid.

To use Stearic acid in Cold Procces soap measure out the desired amount you want to use and put it in a microwave safe container. You’re going to have to melt it in a microwave, this may take a few minites since Steric acid has a high melting point. I would recommend not useing more than 5% your total weight in oils as stearic acid unless youre using a dual lye soliution because a small amount of Stearic Acid granuals goes a long way in hardening your oils. Stearic Acid is also used as a hardener in lotions and balms. I believe the other day I was using one of my beard balms and noticed small hard bits that were forming in the balm. Ive had this Balm for over a year and just started to notice them. The Balm does not smell bad so I know none of it has gone rancid, however it that moment I decided to check out the ingredient in the beard balm I was using. The balm did infact have stearic acid as one of its ingredients. Which makes sense to me as many of the other oils used in the balm were soft oils like Olive Oil or Safflower Oil which would need something like stearic acid or some type of wax to harden the balm.

Conclusion

Stearic Acid being the most commonly found Fatty Acid is used in a number of cosmetic products as a hardener including soap. In addition to Stearic Acid producing a very hard bar of soap its salt, Soduim Stearate produces Soap that has a very long lasting stable lather making it ideal in shaving soaps. Many Sopamakers would recommend using only a little(<1%) Stearic Acid as a hardener but ive found that if properly melted into another softer fat like Lard or Coconut Oil it can be added at a much higher rate and cause little to no issues. If the Stearic Acid isn't completly melted and blended though the rest of the oils before the lye is added you can develope these white stearic grains in your soap. This is also more likely to happen if your oil blend has a very high concentration of stearic and Palmitic Acid, and was used at a low temperature (<70°F) some of the oils can start to solidify and cause stearic spots aswell as false trace. I hope this Information was useful and helps those looking to make a harder bar of soap.