by Megan Kingsley

Created on: January 25, 2010   Last Updated: January 26, 2010

Originally named for the Castile region of Spain, castile soap has long been known for its gentle, soothing properties.  Castile soap has a great reputation for cleansing the skin without stripping oils, and is widely used as baby soap, and for those with problem or extremely sensitive skin such as chemotherapy patients. 

Although commercial manufacturers and some modern soapmakers cut costs by using only 40% or even less olive oil in a recipe and claiming it as castile, true castile soap is made with olive oil for the entire oil amount in the recipe.  In many circles, soap may still be considered castile if 95% of the oils used are olive oil, and in this case, castor oil often makes up the other 5%, imparting greater lather.  100% olive oil soap is mild, but can be slippery with few bubbles.  The addition of castor oil to the recipe retains the soap’s mildness while helping to cut down on the slippery feel and imparting a richer lather.

When making castile soap, there are several types of olive oil to choose from.  If you desire an extremely white bar, extra-virgin olive oil may be the best choice.  However, it is expensive, and many soapmakers feel it does not produce higher-quality soap than less expensive oils; in fact, many feel that the cheaper oils, including olive pomace oil, produce a superior bar.  Once you have selected your olive oil, decide if you will be adding any additional oils to the recipe, such as castor.

Your soap will be made up of three ingredients: water, oils, and sodium hydroxide, commonly known as lye.  Learn to utilize a good lye calculator, and always weigh your ingredients accordingly; never use volume measures.  Many soapmakers rely on Soapcalc.net .  Once you’ve chosen your lye calculator, input the size of the batch you’ve chosen, as well as the oils you wish to use and any other additives (such as color and fragrance) you wish.

To make your soap, don your safety apparel including goggles to protect your eyes, and gloves to cover your hands.   Carefully weight out the water amount, and then slowly sprinkle the weighed amount of lye into the water, stirring carefully until all of the lye is dissolved and the solution is clear.  Set this aside and allow it to cool.  In a large stainless-steel pot, carefully measure out your oils.  Once the lye solution and oils are the same temperature, pour the lye solution into the oils and use a stick-blender to bring the mixture to ‘trace.’  You can mix by hand the old-fashioned way, but castile soap will take literally hours, if not days to reach trace, so a stick-blender is the way to go. 

Once your soap has traced,  add your fragrance if desired, and pour the mixture into your lined mold, cover, and allow the soap to set up and gel for at least 24 hours.  If the soap is still soft, you may wish to leave it in the molds for another day or two.  Once firm enough to remove from the molds without damage, do so and slice the soap as you see fit.  Castile soap is soft and requires a good long cure time—at least 8-12 weeks.  Place the bars in a dry, airy place and turn them over every few days.  After the curing period, your soap is ready to use, although castile soap, like fine wine, tends to get better with age.  Many soapmakers prefer to cure castile soap for several months to a year before using or selling it.

Learn more about this author, Megan Kingsley.
Click here to send this author comments or questions.