DIY Guide to Making Castile Soap

Soap making has been around for 2000 years, but it wasn’t until the 19th century that people learned that it killed bacteria, and was a good form of hygiene. Soap making is easy to do but requires the right tools, protective eyewear and gloves and also requires patience. One of my favorite soaps is Castile soap. Castile was originally made in Spain from their native olive oil, but nowadays castile refers to any soap made with vegetable fat rather than animal fat like tallow. Castile is also considered one of the most high-grade soaps available. Soap can take 2-4 days to make start to finish and many factors can alter the way that it turns out; but soap is almost always usable no matter how it looks it just may not always look pretty!

Soap made from vegetable oil also known as soft fats are in my opinion the best soaps made. The best vegetable oil is coconut oil because it produces a fine sudsing soap, but olive oil is by far the best overall vegetable oil for soap making, so I tend to use both! Soaps made from vegetable oils require less water than traditional soaps but require more drying time. Water is the single biggest ingredient for soap making next to the oils used. It is important to use good clean water. Hard water is not recommended as it has chemicals which will not mix well with the sodium hydroxide, a cleaning agent required to make soap. If distilled water or mineral free water is not an option, you will need to add washing soda or borax in the mix to help neutralize the chemicals. Borax is an additive that can be added to any soap recipe to act as a softener and it holds down the soaps tendency to curd in hard water. The amount used does not effect the quality of the soap. I have used several table spoons to an entire cup and the quality never changes.

Soap making is a chemical process that results in Saponification. When Sodium Hydroxide and vegetable oils are brought together, under the right conditions they make soap, a process known as saponification. Castile soap can take several weeks for complete saponification, a reason that aging is so important in natural soap. Saponification is important because a newly made piece of soap may contain caustic sodium hydroxide, but the longer it ages it dissipates.

img: Eco Living experts


24oz Olive oil

38 oz hemp oil or jojoba oil

24 oz coconut oil

13 oz Sodium hydroxide, SH (94-98%) should not contain nitrates, and can be picked up at the super market

5 c distilled water


Step 1

Slowly add 13 0z of sodium hydroxide to 5 c. cold water. (Sodium hydroxide is very acidic and will burn the skin, so use gloves and wear glasses to prevent splashing in the eyes.) Make sure the container is an unchipped earthenware pitcher or large bowl. (do not use cast iron or metal as it is porous and will leach) Gently stir the SH and water with a wooden spoon until the SH is dissolved, preferably outside. This mixture creates very strong fumes and will make you cough if you inhale them. Stir constantly until the SH is dissolved in the water. Let stand and cool.

Step 2

In a crock pot or large cooking pot heat all the oils together on high. Slowly and gently add the SH and water mixture to the oil mix and stick stir. If you want to add a softener like borax pour it in at this time. Allow the soap to trace (set-up or thicken) and then stir again in one direction. Temperature plays a key role in how quickly soap “sets-up”. More heat tends to quicken the process but can darken the color of your soap. If you are having difficulties with it setting up drop the temperature, or increase it. Sometimes placing in a low temp oven overnight works too. There are no hard and fast rules. Look at the consistency of the soap, the clarity and experiment to get the desired results. Humidity, outside temperature and altitude can all effect the results so practice makes perfect.  Soap will start out dark-colored but as you stir it will get lighter and clearer in appearence. When the cloudiness begins to turn clear, Saponification happens. When it has the consistency of pea soup and drops can be scooped up with your spoon and or the spoon stands up in the mixture, it is ready to mold.

Royalty Free Stock Photography: Two soap and green leaf on wooden

Step 3

The best device for a soap mold is a soaked wooden box that is lined with a damp cotton cloth. If you don’t have a device like this a pyrex pan lined with wax paper works too. Cover the mold with a plastic lid, or cardboard and place a blanket on top to retain heat and moisture while the soap “sets-up”. In this stage saponification is still occurring and is best left alone. When it appears that the soap has “set-up” remove from its’ container and score into bars. Soap can be scored with a wire or a plain ol’ kitchen knife.

Liquid soap

Do steps one and two. Put large pot into the oven and let sit at 200 degrees over night until soap is like a thick gel. Put back on heat and add water to dissolve (start out with about 3-5 c). Once soap is clear (borax can be added to cut down on the sodium hydroxide) let it cool and pour into a jug for storage. 

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Amanda Gates started AB HOME Interiors in the fall of 2004. With over 12 years of experience in the field of interiors, and a passion for all things art and design, Amanda has become an expert on building interiors for an active lifestyle. After six years of working for some of the best design firms on the west coast, Amanda opened AB HOME Interiors after moving to Nashville. Amanda believes that a home should reflect your personality and and encompass your style. An advocate for living a true lifestyle, her firm focuses on bringing you beautiful interiors, that are deceptively functional, and as a result her clients get an amazing space without all the fuss.


  1. How brilliant you have posted this recipe. I got all excited a few months ago about making my own laundry soap, etc, and hunted for a recipe for Castile soap, but none seemed quite do-able. This one is, though, so I look forward to giving it a whirl. x

  2. Sandy says:

    I’ve been looking for a soap recipe and a friend passed this on to me. It sounds great!

    I wanted to ask how and when in the process can I add fragrances such as lavender or ground up almonds etc.

    Thank you so much!

    Merry Christmas!

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