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Hot Process Castile Soap Recipe for Bars or Liquid

Rachel is a soap-making, wine-brewing homesteader and gardener in Minnesota.

How to make homemade Castile soap: bars, liquid, and with various types of oils, including lard.

How to make homemade Castile soap: bars, liquid, and with various types of oils, including lard.

Making Your Own Castile Soap

Castile soap has been all the rage on social media for a while now, and I've seen quite a few recipes being shared so people can avoid buying this expensive product from big stores. But the thing is, pure Castile soap, unlike what you buy in the store, is traditionally made from 100% olive oil, which doesn't actually make great soap. A really good bar of soap is made using a variety of oils that each bring a different trait to the table.

I worked out a simple recipe that is still considered Castile soap because it is more than 50% olive oil, but it incorporates other oils as well, to create a much more balanced, cleansing, and bubbly soap! If you make your own laundry soap, you will also love this recipe for your laundry bars.

This Castile recipe calls for olive oil, coconut oil, castor oil, water, and pure lye (often called sodium hydroxide) and will make about two and a half pounds of soap. If you like to use lard to make soap (I sure do!), I have an alternate recipe for Castile soap made with lard included here for you as well.

How to make homemade bars of castile  soap

How to make homemade bars of castile soap

Basic Soap-Making Safety

I recommend reading my article "Homemade Soap Made Easy" if this is your first time making soap.

Making real soap requires the use of lye (sodium hydroxide), which is a caustic base, so you need to exercise some safety precautions.

When I make soap, I use the following to protect my skin and eyes:

  • Goggles while handling lye
  • Large rubber gloves while handling lye and the soap until it comes out of the mold
  • Long sleeves and pants

If you do get any lye on your skin, don't panic—just splash it off with some pure white vinegar (an acid that will neutralize the basic lye) and then cleanse your skin thoroughly under running water. Keep pets away from soap-making, and use caution and common sense if you want your children involved in the process with you!

Homemade Castile Soap Recipe

Please note: All measurements are by weight, NOT by liquid volume.


  • Olive oil, pure (not extra virgin), 24.5 ounces
  • Coconut oil, 5.5 ounces
  • Castor oil, 1.5
  • Pure lye, 4.0 ounces
  • Water, 10.0 ounces
  • Essential oil or fragrance oil (optional), 1-2 ounces stirred in before molding

How to Make Homemade Castile Soap Bars

  1. In a large non-reactive metal pot, combine the first three ingredients and warm gently, stirring occasionally. The coconut oil needs to melt into a liquid.
  2. Bring the oil mixture to about 115°Fahrenheit.
  3. In a glass jar, add the water. This is important. You must add the water to the jar BEFORE adding the lye to avoid a potential hazard.
  4. Add the lye crystals to the water and stir with a glass or other non-reactive rod or spoon until all the lye has been dissolved.
  5. When all the lye has been dissolved, add the lye solution to the hot oil mixture and stir well.
  6. Stir the soap mixture briskly until it reaches trace. You may want to use an immersion blender to speed up this process.
  7. Once trace is achieved, pour the hot soap mixture carefully into your crock pot. Set the crock pot to high and prepare to watch the cook.

Cooking the Castile Soap

  1. Set your crock pot to the high setting for about 10 minutes, then reduce the heat.
  2. Stir the soap when the edges begin to "creep" up the sides of the crock only enough to keep it from getting out of the crock.
  3. Observe the soap reach a semi-translucent, "applesauce" state, and prepare the mold to plan to put the soap into.
  4. When the soap reaches a semi-translucent, mashed potato-looking state, it is done cooking and ready to go into the mold. You can test doneness by stirring it briskly just a couple of times and watching to see if there is any separation of oils out of the soap mixture.
  5. If using the optional Essential/Fragrance oil, stir in now.
  6. Spoon the hot soap into the mold. It should be quite thick and goopy.

Note: Over-stirring hot process soap can, in my experience, result in unsightly air bubbles and just a general lack of density in the finished soap bars.

There is no need to cover the hot soap once you have put it in the mold. It is fully saponified at this point, meaning no further chemical reaction is in progress, and its only job now is to cool down so that it can be cut into bars!

How to Make Liquid Castile Soap From Castile Bars

While it's totally true that you can make liquid soap a different way, using potassium hydroxide, I made liquid soap directly from my bar soap. It's actually ridiculously easy to do!

  1. Cut one of the Castile soap bars you made into about one-ounce pieces.
  2. Take one ounce of the Castile bar soap and grate it using a cheese or potato grater. The finer, the better!
  3. In a large metal pot, boil as close to a gallon of water as you can manage.
  4. Add the grated Castile soap when the water reaches a rapid boil.
  5. Stir until the grated soap is completely dissolved.
  6. Carefully pour the liquid soap into a bucket. If needed, top off with hot water from your faucet until you reach about one gallon.
  7. Cover the Castile liquid soap with some plastic wrap and let sit overnight.
  8. Bottle as you see fit! I like to use recycled old hand soap bottles with the pumps.

Shelf Life

Where water is involved, bacteria can be present. In general, the pH of soap prevents bacterial or fungal growth, but it's a good thing to be aware of. The bar soap you made with my recipe still contains a small percentage of unsaponified oils, and because we don't use any preservatives in our homemade soaps around here, it is possible for those oils to spoil. I would recommend only storing this liquid soap for about six months, which is why I only make one gallon of it at a time.

How to Make Castile Soap With Lard

This recipe makes about 2 pounds of Castile bar soap, and I must say, is a much more balanced soap than recipes that call for larger percentages of olive oil. It's my personal favorite for soap made with olive oil.

  1. Olive oil, 9.5 ounces
  2. Lard, 7.4 ounces
  3. Coconut oil, 6.0 ounces
  4. Castor oil, 1.0 ounce
  5. Water, 7.6 ounces
  6. Pure Lye, 3.3 ounces

Follow the instructions for making the first recipe to create this soap!

Alternative Cold Process Method

Either of these recipes can be used to make bar soap using the cold process method, rather than the hot process method as prescribed.

To convert these recipes to cold process, make the following changes:

  • Use about double the recommended essential or fragrance oils, unless you don't mind a weaker fragrance
  • Wait for the lye to cool down to about 110* Fahrenheit before adding it to the hot oils at the same temperature
  • Instead of pouring the soap mixture into a crock pot and cooking it, pour it directly into a mold, insulate the mold, and leave it alone for 12-24 hours
  • Cure the cold process Castile soap bars for 3-7 days before testing them for hardness

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2017 Rachel Koski Nielsen


Rachel Koski Nielsen (author) from Pennsylvania to Minnesota on June 07, 2020:


The "cauldron cook" you're talking about is likely referring to an old soap making method called full boil. This uses an unknown concentration of lye, which is why is requires boiling for long periods and then "washing", which is actually a process to neutralize any remaining lye. I wouldn't recommend it when we can just use the correct amount of lye.

If you overcook soap in the hot-process method, it will dry out and make a huge mess. It should only be subjected to heat until the chemical reaction is finished. You can add water as it cooks if it seems to be getting too hard but hasn't gone through the full process yet, but do so carefully and in tiny amounts at a time. Excess water will produce steam that could be a safety concern.

Foxtaillily on October 23, 2019:


So I’m a green soap maker. I’m wanting to focus solely on pure olive oil Castile hard soap to begin. My only question is cook time. In Marseille they cook their soap for 8-10 days it appears & I know that is for shelf life to cook out all oils. What happens when you cook soap at home in smaller batches for lengthy periods? Does it run out of water, oil, get hard? Can you add more water as it cooks? I hear in Marseilles they “wash” their soap after the first couple of days in the cauldron. What does this mean? Is it possible at home?

Beth on July 07, 2018:

Hi there!

Do i still need to let this cure for a few weeks or is just ready to use?

Thanks so much :)

Sp Greaney from Ireland on February 03, 2018:

Very useful hub. I think homemade soaps are better than commericals because at least you know what's in them.