Stearic Acid

Stearic Acid is a saturated fatty acid that contributes to a hard stable bar. This ingredient is usually added into lotions and soaps as a thickener or hardener. It also contributes to stability although it is recommended to use sparingly in cold process soaps, as it is a notorious contributor to a fast trace and even seizing certain recipes, especially ones that are already high in hard butters or fragrance oils that are known to accelerate trace.

Stearic acid is derived from a plant based vegetable, so it is OK to use in vegan recipes. It’s waxy properties a recommended be used at a 0.5% of your oils in cold process soap

The oil highest in stearic acid is soy wax, with a high 87%! Hard utters are high in stearic, as well. Mango, cocoa, shea, kokum, sal, illipe,

Commonly used as a staple ingredient in shaving soap. Some soapers will use a percentage as high as 4% with recipes containing soft oils with mostly unsaturated fatty acid profiles.

Ricinoleic Acid

Ricinoleic is an unsaturated fatty acid that contributes to the conditioning/moisturizing levels, and the stability of lather. This fat has properties attributing to a little slip and glide to the lather. Castor oil is the only common soap making oil known to contain ricinoleic acid, and it’s a super high 90%! The typical range for castor oil added into a recipe is 5%. Castor oil contributes to a boost in lather and will make a recipe trace faster than without adding it.

Palmitic Acid

Palmitic is a saturated fatty acid that contributes a long shelf life, a hard bar, and stable creamy lather. Oils with a high profile in palmitic fatty acid add this to increase stability in the bar. The lather from the palmitic oils create a dense slick lather, or minimal lather with tiny smooth bubbles. Popular soap making oils with a palmitic profile are, of course palm shortening, palm oils, and palm kernel oil, but there are many others as well. Animal fats are high in a palmitic profile, such as lard and the family of tallow. In plant based oils palmitic profiles include Cocoa butter (an alternative to palm oil). The average percentage of palmitic acid in the favorite soap recipes of soap makers polled rounds in at 15%,. Most recipes measure at 10% to 20% palmitic acid. This is not a hard rule. Some of my favorite recipe include 35%.

Making piped decorations high in palmitic type oils helps to contribute to solid shapes for flowers and designs. The consequence of too much palmitic oil is that the trace can thicken quickly so piped designs have to be timed quickly to keep the recipe from setting up too fast.

Oleic Acid

Oleic acid seems to be one of the fundamental base fatty acids around which soap makers build their recipes.


It contributes to a moisturizing and conditioning bar, yet is slow to trace and it offers a long shelf life. The most common oil with the highest profile in oleic acid is olive oil. Oleic acid can make up 100% of a recipe, and is famously known as Castile Soap. Other oils include sunflower and safflower oils, canola, sweet almond, apricot and peach kernel and avocado. Less common are carrot seed, pataua, camellia, papaya, marula, hazelnut, moringa, buriti, bear tallow, plum kernel, pistachio, macadamia nut, karanja.

Recently on retail shelves products high in olive oil have been marketed as exceptionally moisturizing and nourishing and branded as a higher quality oil to be desired in hair care and lotions. The actuality is the opposite. Products high in oleic acid are actually drying to the skin and are not as moisturizing as soy bean oil, however, products with olive oil and avocado oil are gentle to the skin.

Myristic acid

Myristic acid is a saturated fatty acid profile that creates a dry hard bar of soap with fluffy lather. Myristic is often associated when combined with Lauric fatty acid because there is no common oil for soap making that in itself has a high myristic acid profile. Most commonly myristic acid in a soap recipe comes from coconut oil, which is primarily selected for it lauric acid qualities. Most oils with a lauric acid profile contain a lesser amount of myristic acid in its blend. The range of myristic acid can range from 3% to 20% in one of these oils. The next most popular soap making oil, second to coconut oil is babassu oil which is similar to coconut in profile and also has a melting point of 76 degrees. Both of these oils lean toward drying properties, so soaps used with these oils should be well balanced with other fatty acid profiles.

Linoleic Acid

Linoleic is an unsaturated fatty acid that contributes to the conditioning/moisturizing of skin care products, This is not used in high amounts in cold process recipes and ranges in the single digits in recipe %s. Soaps high in Linoleic acid do not have a long shelf life, and almost always soft oils like soy bean, canola, rape seed oil and hybrid vegetable oils.

Lauric acid

Lauric Acid is a type of fatty acid profile that contributes to the qualities of your hand made soap. Adding lauric acid to your recipe profile comes from the type of oils selected. Oils high in lauric acid are coconut, babassu, palm kernel oil, cohune, tucuma, and murumuru butter. Lauric acid is a saturated fat and a medium-chain fatty acid, made up of a twelve atom carbon chain. This profile will make a bar that has big fluffy bubbles and creates a hard solid bar of soap with high cleansing properties. This is not an acid that lasts a long time on storage shelves, so it is important to have a well balanced bar with other fatty acid profiles. A typical balance recipe will have a profile of Lauric acid in the range of 5% to 35%.

Iodine

For soap makers Iodine is an aspect of measurement that appears in many soap making calculators that help gauge the stability in a hand made bath of soap. Specifically, iodine is the measurement of the polyunsaturated quality of the fatty acid profile. The higher the number the more polyunsaturated. This a a rough measure of how easy it is to saponify the fats in a soap recipe. It is not, by any means the most valuable measurement, and was widely used at the beginning of the century for large commercial soap making companies as a tool of measurement for large batches. This was meant to be a one number, quick glance of the quality and shelf life of the product.

Since higher saturated fats in your soap are usually made with harder oils logic follows that the lower the Iodine number in a soap recipe the harder the bar of soap will be and the less the conditioning qualities and vice versa.

For hand craft and small batch soap makers, it may be helpful to know that the lower the Iodine number in the recipe the faster the soap will trace during the emulsification process.

For designs that require a thick pudding texture an Iodine number near or below 50 is fine, but if the goal in the recipe is to get light wispy swirls the recipe may work better with a higher Iodine number, above 50, but under 65 to keep the recipe balanced and the integrity of the bar to keep a stable shelf life.


Definition: number of grams of iodine that will react with the double bonds in 100 grams of fats or oils.

INS

The INS value in a soap recipe is related to iodine as it relates to the saponification value in the entire recipe of soap.This is a number that was formulated in the 1930’s with vague origins. The first time the term INS is widely sourced it is in Dr. Robert McDaniel’s book, Essentially Soap who says that the INS is a combination of the iodine and SAP value in a weighted average.

According to Dr. McDaniel the ideal INS number to aim for is 160 with a range of 147 – 170.


Other sources describe the INS as the saponification value minus the iodine number. Iodine number is a measure of the unsaturated bonds in the fats. As a general guideline, the more soft oils the more unsaturated, and so the higher iodine number. Because of the rough classification of soap ‘quality’ and and more predictable outcome with fewer oil combinations and ingredients, the INS number was over all a more useful guideline with early large industrial batches, while less important with small hand crafted batches where an artisan soap maker is carefully reviewing the balance of oils and butters while making a smaller amount and focusing on a higher quality result. The INS number was a way to evaluate the ease of saponification and stability in a recipe when batches were made on large scale and possible less human scrutiny over the entire process.

For the hand craft soap maker the INS number can be used to predict the shelf life of a batch. Higher numbers are attributed to saturated fats. These oils saponify more easily, and harder, and make a more cleansing bar. These oils are more stable and will last on the shelf longer than unsaturated fats once turned into soap. Coconut is at the top of the list at an INS of about 258, followed by palm kernel, tallow, cocoa butter, palm oil, lard, and shea with INS of 115-230.

Lower INS numbers are attributed to unsaturated fats and soft oils. Therefor, the lower the INS number the less resistant the batch will be to the DOS (Dreaded Orange Spots) phenomena that can happen as the floating oils degrade over time during storage. The help protect against DOS the INS number should be evenly balanced (around 160 or higher)Oils that contribute to DOS are lower in iodine, sch as: polyunsaturated oils such as canola, corn, soy, sunflower, safflower. These oils should remain lower in percentage in the total weight of the recipe.

Hardness

Hardness in soap making refers to the hardness of the bar of soap after it has finished the curing process. When crafting a soap recipe many calculators will offer a hardness range. This is typically a number between 29 to 54 with the higher number being a harder bar of soap. This number is a general guideline and does not mean that a number outside this range will not produce a perfectly fine bar of soap. Hardness is typically referred to a solid bar of soap made with NaOH -, Sodium Hydroxide, as any soap made with KOH – Potassium Hydroxide will result in a liquid or creamy product and offer no hardness at all.

The hardness of a bar of soap will be affected by the fatty acid profile of the oils used in the recipe. As a general rule hard oils will create a harder bar of soap. Palm, Lard, Tallow, Coconut Oils, Bees wax, Mango Butter, and Shea Butter will all produce a hard bar of soap. As an example commercial brands like Ivory, Dove, Dial, Irish Spring, Jergens, Nivea are all primarily made from tallow resulting in the hard waxy bars most people recognize.

Soft oils or liquid oils will produce a softer bar of soap that will create a softer and more moisturizing effect. Olive oil is an exception. Olive oil take a longer time to cure and may seem soft for a very long time upon its unmolding, but a bar of soap made primarily from olive oil will result in a very hard bar that will need to be sliced before it has fully cured.