Selecting soap making oils and butters is a fun and personal process. Each oil and butter contributes various properties to the finished bar. For example, some oils may give a silky lather, while others may contribute extra moisturizing properties. Many soapers spend years perfecting their cold process recipes to create what they consider to be “the perfect bar.” The great thing about making your own soap is recipes can be altered depending on personal preference, or with what oils you have on hand. But be careful, not every oil substitution is made equally!
Before jumping into the complicated world of substituting oil in cold process recipes, I recommend reading the Free Beginner’s Guide to Soapmaking: Common Soapmaking Oils blog post. The key to substituting oils is to find an oil with similar properties in terms of how it behaves in soap. The Common Soapmaking Oils blog post provides a brief profile on each oil including what properties it contributes to soap, along with recommended usage rates.
In addition to this handy blog post, I also recommend becoming familiar with the Lye Calculator. The calculator is key for determining how much lye is necessary to turn the oils in your recipe into soap. For more information on how to use the calculator, check out the Using the Lye Calculator blog post. When substituting oils in a recipe, remember: always run the recipe through the Lye Calculator again. Even if you are using the same amount of oil, the amount of lye necessary to turn the oil into soap may be different. The Bramble Berry Lye Calculator is also available on your phone via the Soap Lye Calculator App! Available for both iPhone and Android, just search “Bramble Berry” to download.
The amount of lye necessary for the recipe depends on the saponification value of each oil. The saponification value (aka: SAP value) refers to the amount of lye it takes to turn 1 gram of oil into 1 gram of soap. The SAP value for each oil and butter may vary slightly depending on where it comes from. Because SAP values can vary, one lye calculator may give slightly different results than another calculator. When substituting oils in recipes, the SAP value can be helpful to identify oils that behave similarly. Keep in mind the SAP value does not reveal the characteristics (such as lather and moisture) that the oil gives to soap.