INS And Iodine Levels In Soapmaking

Creating the ideal bar of soap is the holy grail of soapmaking for many a modern soapmaker. The more we learn about the fatty acids that make up oils, the better our potential. The fatty acids we are concerned with in soapmaking are: lauric, myristic, palmitic, stearic, ricinoleic, oleic, linoleic and linolenic.

​Even armed with the knowledge of fatty acids, the concepts of INS and Iodine levels seem to be among the best kept secrets of soapmaking. Few understand them, but those using Soap Calc have, no doubt, seen them and checked to see if their formulas are in the acceptable range. Yet, what are they exactly?

The iodine level refers to the polyunsaturated fats in a given soap formula and is measured by the amount of iodine that can be dissolved per gram of fat or oil. High iodine levels usually produce soft soap subject to rancidity or DOS (Dreaded Orange Spots). It is logical then, to conclude that oils with high iodine numbers are best used at lower percentages to make a bar that resists rancidity. Hint: these oils are high in linoleic and linolenic fatty acids.

The INS of soap is an historical method developed in the 1930s to determine the most pleasing soap to consumers. Dr. Bob McDaniel, author of Essentially Soap, informs us that the INS is a combination of the SAP value and iodine level, and 160 is considered ideal for soap. It is now out of print, but if you have the opportunity to purchase Dr. Bob’s book, do add it to your library as a great reference for making bar soap. Most soapmakers who make use of INS keep their formulas between 136 and 170, as recommended by SoapCalc.

Can the soapmaker create a great bar of soap without understanding Iodine and INS? Is it foolproof? Of course you can; but in the constant quest to educate ourselves, learning what these terms mean can help guide us to better quality soap. Knowing the INS number of a calculated formula can help determine if it will result in a pleasing bar. It is less helpful with one oil bars, such as the classic castile bar and superfatting well over the established ranges, such as coconut oil bars superfatted at 20%. Overall, nevertheless, it is a helpful indicator of a good general bathing soap and worth exploring as you learn about making soap.

Do you pay attention to Iodine and INS levels?

Until next time, may your days be filled with bubbles and wax.

Beth Byrne for Making Soap, Cosmetics & Candles Magazine

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