Crockpot Castile Soap

When I started making soap, I learned from the book Handcrafted Soap, by Dolores Boone. It is well worn – though I don’t follow the recipes, I follow the technique. I love the hot process soap method because it is fast and pretty hands-off. My style. My soap can be in the molds in about an hour and half, with only 15 minutes of hands-on time. Then the next day, it takes about 15 minutes to cut up the bars. Half hour soap! :D

I call my soap castile soap, though it is not true castile soap (100% olive oil). The olive oil makes a very hard bar of soap, but it takes sooooo long to bring to trace (you’ll see what that is) and to harden, that I prefer to use half coconut oil and half olive oil for the major oils. I use castor oil for conditioning, just a bit of it. And I add stearic acid, just a bit, for hardening. You can also use beeswax for hardening. I have done both. Beeswax tends to boil over more in the crockpot than stearic acid. Been there, done that. (When soap gets too hot.)

My recipe has been run through the Lye Calculator at MMS Sage. This is a fantastic tool – so thorough and so easy! You put in your oils and it pushes out the proper amount of caustic (in this case, sodium hydroxide or lye). When I make soap, I want there to be a bit more oil — this is called super-fatting. The oil and the lye are going to chemically react to produce soap, but there’s no way we can count all the molecules and make sure this chemical reaction is totally even. We don’t want to end up with lye unreacted! By super-fatting, we ensure that extra fat is left unreacted (instead of extra lye unreacted).

On the Lye Calculator, MMS Sage gives you amounts of lye to use depending on the percentage of super-fatting. I choose 5% super-fatting. This means there’s 5% excess fat and ensures all the lye is reacted/turned into soap. Make sense?

Take a look at this: a PDF of the results of running my amounts of oil through the lye calculator at MMS Sage. On that you can see the various percentages of super-fatting in my recipe.

In this post is my adaptation of the method in Handcrafted Soap by Dolores Boone. I see her book is out of print on Amazon? I don’t have time to chase it down, but just in case you can’t find it, I’ll also include a paraphrase of her method that I typed up a few years ago for a friend. I haven’t edited it or looked at it since. :) Here it is.

Safety Equipment

  • Protective clothing
  • Disposable plastic gloves
  • Long-sleeve Shirt
  • Safety glasses or face shield

Equipment (not all may be used in this recipe)

  • Cookware — stainless steel pot for melting oils
  • Crockpot — older models don’t heat as hot, which is a benefit
  • Digital scale
  • Stick blender
  • Glass measuring cups
  • Small glass bowls (for smaller measurements)
  • Long-handled plastic spoon
  • Rubber spatula
  • Metal ice cream spade
  • Funnel (filling molds)
  • Pitcher filled with soapy vinegar mixture

Ingredients (by weight, unless noted)

  • 26 ounces pomace olive oil
  • 26 ounces coconut oil
  • 2 ounces castor oil
  • 1.2 ounces stearic acid (optional, for hardening)
  • 8.38 ounces sodium hydroxide (lye)
  • 14 to 20 ounces distilled water — not by weight (I use 18 ounces)

Note: if you omit the stearic acid or change any oil kinds or amounts, rerun the lye calculator at MMS Sage. If you use beeswax instead of stearic acid, use 1.5 ounces (and run it all through the calculator).


Measure the solid oils (oils which are solid at room temperature) using a scale (tared to eliminate the weight of the glass measuring cups). Pictured: coconut oil and stearic acid.

Put in a pot on low heat to melt slowly – don’t let them get too hot! I usually remove from heat when there are still tiny bits of unmelted oil.

Measure the liquid oils (oils which are liquid at room temperature) and put in the crockpot. Turn on to low to let the oils heat gently. Once again, don’t let it get too hot! I use an old crockpot that doesn’t get that hot. Cover while heating (not pictured).

When the solid oils are just about melted, add to the liquid oils in the crockpot and cover.

Measure the distilled water in a 4-cup measuring cup (not pictured). Measure the sodium hydroxide (lye) by weight into a separate, smaller measuring cup. Wear protective clothing and safety equipment when working with lye.

Carefully, while stirring, pour the lye into the water. I like to do this underneath the stove’s vent, so the fumes go outside. Stir until all crystals are dissolved. It will get very, very hot, so don’t touch the glass container. Leave under the hood, with the fan on, for about 5 to 10 minutes to cool down.

Again while stirring, and pouring carefully (impossible to do while photographing), add the lye/water solution to the oils in the crockpot. Use a soapy/vinegar/water mixture in the sink to rinse the containers and utensils that touched lye to neutralize this caustic.

Stir briefly, then switch to using a stick blender and blend until the mixture reaches “trace” — which is when it thickens. It will go from clear to opaque, and resembles vanilla pudding when done. The mixture, when dripped off the stick blender, will stay in visible ridges, rather than the mixture collapsing back into a smooth top. With this soap, it takes about 2 to 3 minutes. With pure olive oil soap, it can take 5 minutes or more to achieve trace.

Cover and let “cook” for about an hour.

During the cooking time, the mixture will change back to translucent. It will raise up at the sides, like waves. This is after about 15-20 minutes in my picture.

By the end of the cooking, the whole mixture will be translucent and the center of the mixture will be collapsed with the “waves” rolled into the center. (My picture of this stage is not very good, but it does happen.)

Also, there may or may not be liquid pooled in the center low point. This is glycerin, a natural byproduct of saponfication (the soap-making chemical reaction). Just stir this back in – it is very good for your skin!

Turn off the crockpot. During the cooking time, prepare your molds. I use two plastic drawer trays lined with freezer paper. Usually, I use freezer paper (shiny side up). During this soap making, I was out of that, so I used parchment paper that I greased with coconut oil; worked fine.

Fill the mold(s) with the hot soap mixture. Tap up and down on the counter or a floor to evenly distribute the mixture. You can use your hands, but be careful and touch lightly as the mixture is very hot! (And you need it to be hot to fill the mold properly.)

Now the soap in the mold(s) need to cool/harden, at least overnight. The crock can be scraped clean for instant delight – soap that’s ready to use!

When hardened and cooled, lift the paper to pull the soap out of the mold(s).

Peel the paper off the soap block. Put the block on a cutting board and use a big knife to cut into bars.

The bars still need to harden significantly and will do this over time. Keep them in a cool location with good airflow. I keep a tray of upright bars in my bathroom. We use one, the rest age, we use another, the rest keep aging… If upright, more air can flow and they’ll harden more evenly and faster. Rotate them infrequently if you’d like.

So I think that is it! If I missed anything, please ask, and I’ll try to clarify. :D Enjoy!


  1. Hi,

    I am new to the soap making process and I have only used the crockpot form which I love!! My question I’m hoping you can answer is: Are the recipes different between cold and hot processing. I bought oils and butters from The Soap Dish, but the recipe I found for hot processing doesn’t call for any of them. I bought shea butter, palm Oil, and cocoa butter, so I’m looking for hot process recipes that might use those. Do you have any advice?

    • You can use the same recipes, however if you have a high amount of linoleum, recinoleic or linolenic fatty acid oils your will know that your soap will take as long to harden because of the oil combination. If you know your oils, you can up lye, or decrease water (if you are experienced enough) to help it harden better – or better yet, to tweak the recipe to have a hard, yet emollient soap.

      I like HP soap because I could experiment to see immediately what any oil will do as far as hardness and emolliency. In that way I was able to put together a new recipe and know exactly what it would feel like, and do, when finished.

      So, I recommend that any new soap maker make themselves a few ½ to 1 lb batches in a tiny crockpot and really have fun experimenting. ????

  2. Jocelan says:

    Thanks for the info,Im new to this so i will try this method.Do you have email signup?

  3. A friend of mine gave me a bar of homemade soap recently in a care package. I love the soap and it sparked my interest in the art of soap making. This particular bar is lemon scented. I did not see any mention of the amount of scents or oils to use or how to calculate them if you wanted to add them. Could you help me with this. Read several other sites and think I want to give your method a test. Love the crock pot idea. Thank you.

  4. I found most of these incredients @ my local food co-op. Lye @ a hardware store, and I found Stearic Acid @ a bee keeping store, along with bee wax, which I used instead, and found the molds there too. Thanks for this blog, I had fun making soap!!

  5. Hi! Just bounced over from Frugally Sustainable where she mentioned your blog as one to check out for making hot method soap. I have a couple of questions that you might or might not be able to help with.

    Once the soap is finished and hardened and cut into bars, can you reheat it to liquid again to add essential oils or other fragrances?

    Also, can you reheat to liquid and add something like water to make it a liquid soap like you can store bought soap?

    Thanks! Love the blog!
    labbie1´s last blog post ..Friday Fun #3–Here’s Your Sign…

    • What you are proposing to do is called Re-batching, and yes you can do that but it will be vaseline quality not liquid. If you do it as liquid it will take forever to dry. IMO it is best to add the fragrances/eo’s. additives – after the cook instead. If you want to do several scents, just separate after the cook and do the scents separately.

      Soap made with NaOH will always attempt to go back to its natural purpose – as a solid. You are better off not trying to make a solid liquid in large batches. KOH is the lye for liquid soaps.

  6. Estelle Stone says:

    I have a question: I am a novice to soapmaking. (Only two batches so far) No one told me that soap stinks! ;-) Is it me, or does it smell bad while cooking?? Someone, help!!

    • Some oils or ingredients smell more than others. Cooking too hot or to long, or animal fats and goat milk, will smell stronger. These should fade. Chemically processed oils such as Pomace olive oil, may or may not smell depending on its purity after the chemical is “removed”.

    • I once made the mistake of using goats milk from a friends goat. PHEW! I threw it out. Smelled just like – well, goats. If you want to make goats milk soap, use DEODORIZED goats milk. Since I’ve only seen it at the store in little tin cans, it’s not economically feasible for me. Cows milk on the other hand is awesome, just be sure to use whole milk (for the fat) or add a scant 1/4c of cream to the batch to superfat it.

      When my husband was in the hospital for 8 months he begged me to bring milk soap from home because the hospital soap was drying him out so much.

  7. I’ve always wanted to make my own soap!! Any suggestions? I’m a newbie !!!

  8. Hi im having problems finding these ingredients sold in ounces do you know what they’d be in ml?
    Also could I use regual olive oil instead of pomace?
    Thankyou :)

  9. I would like to address a couple comments, but can’t find them readily on the links supplies, so will do so here.

    To AUTHOR: TODD No, drain opener is not 100% pure lye, most have metal shavings or other ingredients in them to cut through clogs. Any Chemical Company will have it in bulk, but rules and prices vary. Here in Seattle I can get 50 lb bags for about $1.00 – $1.50/lb depending on the grade.

    To AUTHOR: ESTELLE STONE Some oils or ingredients smell more than others. Cooking too hot or to long, or animal fats and goat milk, will smell stronger. These should fade. Chemically processed oils such as Pomace olive oil, may or may not smell depending on its purity after the chemical is “removed”.

    I will need to stop trying to help. I just do not have the time it takes me on this list to try to find the posts that come to my mail box. I don’t know it is this way with PC’s but my MAC will not take me direct to the question posted.

    Best of luck on your endeavors.

    Delores Boone Kirkwood

  10. STOP!! You cannot use soap right away if you’ve made it with lye! It takes a few weeks for the lye not to be caustic anymore. Use right away and expect to get burns and redness on your skin.

  11. kim semthiti says:

    I ‘m glad to learn how to make soap.

  12. How many pounds of soap does this make?

    • Millie Copper says:

      Hi Loyda,

      It’s something like 50-some ounces. You can run the values through the lye calculator and it will tell you the yield in ounces.

  13. lamonte salter says:

    I dont have a stick blender so is it ok to use a hand mixer.
    Also how long did the drying prossec take and can I add essential oils to the mix.

  14. lamonte salter says:

    can i mix the indredients in a ceramic pot

  15. This is a bastille soap not a castile soap. Castile is pure olive oil. however this is a super easy recipe for hot process. thanks for sharing

  16. I can’t seem to find a cheap immersion blender. Could I use my small hand mixer on low? I have two so the older one wouldn’t be missed if it had to dedicate it to soap.


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