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.
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 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.