Many people swear by Castile soap. They feel that it is the purest, gentlest, most wonderful soap on earth.
Castile is a soap that originated in Castile, Spain. They have an abundant supply of olives there, thus they have plentiful olive oil to make soap with. The original Castile soaps are hand stirred and made with local sea water. This soap isn’t quite that fancy, but will produce the same type of gentle, pure, wonderful Castile soap.
In today’s soap making lingo, Castile is just a soap that is made with 100% olive oil and no other oils.
Note: I am not endorsed by, affiliated with, paid or connected in any way with any of the vendors or brands that I list on this page. I am simply their customer, and I include brands and links only so you can have all of the information about what was used in this recipe.
To make the soap into cubes, use a cube mold such as this one from Brambleberry. You can use any mold you like though — the cubes are just a suggestion.
The recipe below will create six 5 ounce (141.7 gram) cubes. The total soap batter volume is approximately 30 ounces (850.5 grams).
- Pure Olive Oil – 19.0 ounces (538.6 grams)
- I use Kirkland Pure Olive Oil purchased at Costco
- Distilled Water – 7.2 ounces (204.7 grams) (38% solution)
- Sodium Hydroxide Lye – 2.5 ounces (69.3 grams)
- Optional: Sodium Lactate – 1.5 teaspoons
- Optional: Essential oils or Fragrance Oils.
- The recipe as shown uses .8 ounces (22.7 grams) bay rum essential oil from Camden Grey.
- Optional: Colorants such as oxides or micas
- The recipe as shown uses 1 microscoop of hydrated chrome green pigment.
Prepare the Work Space:
- Clear your workspace and keep it free of children, pets and any people who won’t be wearing safety gear for the duration of the session.
- Gather the ingredients and equipment needed to make the soap. Arrange the workspace.
- It helps to place all of the ingredients to your left side and then as you add them to the mixture, move them to your right side. Then if you get interrupted during your session, you will automatically know which ingredients have already been added or not.
Measure, Melt and Mix the Oils:
- Measure the olive oil using a digital kitchen scale and put it into a mixing bowl.
- Heat the oil in the microwave or over a double-boiler until it is about 130 degrees Fahrenheit. Set it aside for a later step.
Prepare the Colorants / Fragrances:
- If using essential oils or fragrance oils, pre-dilute them in 1 tablespoon of oil taken from the mixing bowl.
- I find it works well to weigh the fragrances into a shot glass and stir the oil into that.
- The amount of fragrance or essential oil to use depends on the specific ones you are using. Consult a fragrance calculator to determine the correct amount. For the bay rum essential oil, the right amount was .8 ounces to achieve a medium scent.
- If using colorants, pre-disperse them by taking 1 tablespoon of oil from the mixing bowl and mixing in the colorant until all the lumps are dissolved.
- I find it works well to put the colorants into a shot glass and stir the oil into that. The amount of colorant you use is up to you, depending on the color depth you want in the finished soap.
- Beware that using too much colorant can cause colored lather or stain wash cloths. For this recipe, I used only 1 microscoop (about .15 cc’s) of colorant to achieve a light color.
Prepare the Lye Solution:
- Put on the safety gear (safety glasses, nitrile or rubber gloves, long sleeves, pants, shoes) and open a window.
- Measure the distilled water, using the digital scale. (If you add a few ice cubes as part of the water weight, it will keep the lye solution cool and you won’t have to wait so long for it to get to the right temperature). Put the water container into the sink.
- Weigh the lye, being careful not to scatter any granules or flakes on the counter or floor.
- Stir the lye into the water and keep stirring until it dissolves. You should keep stirring until there are no more undissolved crystals or flakes and the solution is clear like water.
- Add the sodium lactate to the lye solution and stir well. This is an optional step, but it will help the soap to harden up faster so that you an unmold it.
- Take the temperature of the oils and lye. Ideally, they should be within 10 degrees of each other.
- For example, if the lye solution is 110 degrees Fahrenheit and the oils are 119 degrees, it is fine. But if the lye solution is 180 degrees and the oils are 110 degrees, it is not fine. Wait until they are at the right temperature, and ideally under 120 degrees farenheit.
- You can cool one or both of them off by making an ice bath in the sink. Plug the sink and put some cold water (maybe a couple of inches) and a scoop or two of ice cubes into the sink. Place the oils or lye solution container into the sink, being careful not to spill it. Stir until the temperature reduces.
Mix the Lye Solution and Oils:
- When the oils and lye are at the proper temperature, carefully pour the lye into the oil mixing bowl. It helps if you can pour it down the spatula or the neck of the stick blender to prevent air bubbles.
- Stir by hand with the spatula for a couple of minutes and then, using the stick blender, mix it alternating with the stick blender on and then stirring with the stick blender off. This is pure olive oil soap so it will take a long time to get to trace. Just keep stirring and blending.
Add the Colorants / Fragrances:
- When the batter gets to thin trace it is time to add the colorants and fragrance if you are using them. Simply scoop them into the soap batter and stir them in.
- Thin trace looks like thin pudding. When you drizzle some of the batter on the top with the spatula, it will sit there for a couple of seconds before soaking back into the mixture.
Pour the Soap into the Mold:
- Pour the soap in the mold cavities.
- Gently tap the mold on the table a few times to remove air bubbles.
Insulate the Mold and Gel the Soap:
- Cover the mold with something like a piece of cardboard. Wrap towels or blankets around it to keep it warm. This helps it to saponify and to go through the gel phase which will make the colors brighter and the soap harder.
Do the Cleanup:
- Clean up the dirty dishes by wiping the excess batter out with paper towel. Dispose of the paper towel in a plastic bag (to prevent accidental exposure to the raw soap batter.
- Wash the dishes and the work surface with hot soapy water.
- You can now shut the window and remove the safety gear.
Unmold and Cure the Soap:
- After 24 hours remove the insulation and cover.
- Since this is Castile soap, it can take up to a week or longer before it is ready to take out of the mold. Be patient. If you unmold too early you can wreck the soap. Leaving it in the mold too long won’t cause any issues.
- Every couple of days, carefully try to peel the side of the mold away from the soap. If it is sticking, it is not ready. If it releases cleanly and the soap feels pretty solid, you can proceed to unmold it. Otherwise wait a couple more days and try again.
- Once you unmold the soap, put it somewhere that has good ventilation (like out in the open on a table, buffet, or desk – but not in a closed drawer or closet). Leave it there for 8 weeks. Castile takes longer to cure than other soap does. Turn it once in a while to facilitate even drying.
- Optional: If you have a soap stamp, a few days after you unmold the soap, stamp a design into it.
- The longer Castile soap cures, the better it gets. At first it might be a little bit gooey. Wait a couple more months and it will be nice. Wait 6 months to a year and it will be fantastic!
Even though this is a 100% Olive Oil, Castile soap, you can still incorporate different liquids into the mix. This can improve the lather. For example, it would be lovely if made with goat milk or buttermilk instead of distilled water.
You can do this by completely replacing all of the distilled water with frozen milk instead. Or you can use a partial amount of milk, added at trace. (Just figure out how much water you need to make the lye solution – usually twice as much water as lye) and add the rest of the liquid volume in the form of the milk, when the soap gets to trace. In this recipe, that would be about 2 ounces of milk and 5.2 ounces of water.
You can also change out the fragrances and colorants to make a variety of different soaps. I have made this soap into a pink soap with Litsea, Grapefruit and Bergamot essential oils.
Since this is a cold process soap recipe, you can also make the cubes more interesting by incorporating multiple colors and doing an in-the-pot swirl design. It would look something like these lilac soap cubes: