Making Hot Processed Soap

I have been making soap for several years now but I had never made hot processed soap before this last weekend.

If you are not a soap maker you may not realize that there are two ways to make soap. One is called cold processed and the other hot processed. Here is the difference:

Cold Processed (CP): This method involves combining your liquid/lye mixture with your oils and stirring until the mixture thickens (also known as “trace”) . Then pouring the mixture into molds. In a day or two you unmold, cut the bars and let the soap lay out on a flat surface to cure anywhere from 3 to 6 weeks depending on the recipe. This ensures the soap is free from all traces of lye.

Hot Processed (HP): You follow the same procedures as CP but instead of pouring into your mold you keep cooking the soap. The soap is heated and cooked all the way through to the end (meaning there is no traces of lye left in the soap). After you remove it from the mold you can cut the bars and pretty much use them right away.

I have always used the cold processed method for many reasons (the soap is smoother in texture, looks nicer, essential oils are easier to add, etc..). But every now and again I like to have a little fun time with my soap making. So over the weekend I made a batch of HP soap in my crockpot. It was pretty simple to make (this is coming from an experienced soap maker!), and it was fun.

If you are not familiar with making soap you will want to make sure you are prepared with information and the proper equipment before you start. I don’t go into a lot of that in this blog post mostly because I already have a few web pages on making soap (   ) and an entire ebook on how to make soap, step by step filled with pictures and information (  ) … so this little tutorial is showing just the basics of what I did. Please be knowledgeable on proper soap making procedures and cautions concerning the use of lye.

Here is my recipe…

Crystal's HP Crockpot Soap
26 oz olive oil
6 oz coconut oil
3 oz. castor oil

4.75 oz. lye
12 oz. water

1 oz fragrance oil

First of all I gathered together all my ingredients. In the picture below you can see my oils all measured out by weight (3 types of oils), the little dark colored bottle is my scent oil (I had a 1 oz sample bottle of Lemon Sugar fragrance oil and it was perfect for this batch) and on the right my water and lye…

Here is my mold… I used a small cardboard box (this recipe needs a mold that will hold 48 oz) lined with plastic..

I started by setting my crockpot on high and adding the coconut oil (any hard oils are added first to melt). While that was melting I mixed up my water and lye. When the lye and water were mixed and the coconut oil was melted I turned the crockpot to low and then added the olive oil and the castor oil to the crockpot…

Now it was time to add the lye/water mix.. unlike CP soap, the temperature of the oils and lye don’t matter when making HP soap. When you add the lye/water mix you should be stirring constantly, I found this a little hard to do and take the pic! :) ..

As soon as it was stirred in I switched to my stick blender and mixed it up..

Until the mixture reached “trace”… this is where the soap is looking like thick pudding/gravy... (it is can be hard to get a good pic of trace..).. Then put the lid on the crockpot and wait..

Now this is the point it would be put into molds if I was making CP soap.. but instead I continued to cook the soap and watched as it went through the various stages of its chemical reaction called, saponification.. this is the process of oils, water&lye becoming soap…

After about 15 to 20 minutes my mixture was looking like mashed potatoes..

After another 20 or so minutes my soap looked a bit like applesauce in texture..

And another 20 min later I had a waxy Vaseline look. I touched a bit of the soap and rubbed it on my fingers and it felt like soap, then I did the zap test.. put a little on my tongue. If there had been any lye still left in the soap I would have felt a little zap.. but I did not, so I knew I had reached my goal.

Then I added my scent oil ..

Now I was ready to spoon it into my mold. I had to spoon the soap into the mold and then every so often tap the mold on the counter to make sure I got any air bubbles out. The soap at this point is very thick to work with. When I got it all in the mold I used a piece of plastic wrap to help smooth the surface..

24 hours later I took it out of the mold..

24 hours after that I cut it into bars. I ended up with about 9 (5.25 oz)bars…

My soap is still a bit soft so I plan to let it sit and harden up before I use it. I suspect the reason it is still on the soft side is because the soap is made mostly from olive oil (olive oil takes longer to harden up than other oils). I am excited to try it out when it is done. Olive oil soaps are extremely mild and gentle on your skin.



  1. This sounds SO easy, I am a beginner soaper but will try this as soon as the holidays are over and I have time to breath.

    Thanks for a great post and pics

  2. This looks so easy. I have been using the cold process to make my soap.

    Have a wonderful day.


  3. Crystal,
    I have never made soap before but it looks like something fun to try. Thank You for posting this mini tutorial!
    Sarah L.

  4. This is really neat! We grew up making our own soap, my mom's hobby and income. People would always talk about it as "standing over the kettle and boiling the soap..." -My mom made cold pressed. Now I "see" minus the crockpot, what the old timers were meaning, I had thought it had to do with wood ashes they got their lye from! We will have to give it a try. Thanks for the tutorial!

  5. Do you keep a crockpot especially for soap making? I just can't imagine using it for meals!!

  6. No I don't Anonymous.. when it is all made you have soap.. and you just wash the crockpot... :) no worries..

  7. Thanks for sharing - it does look easy! You mentioned getting zapped if the lye is still present. Is this something I should be concerned with if there IS lye? It won't kill me, right? LOL

  8. Question for ya! I made CP soap once! It hardened and everything and I figured out the process, but the bars are so slimy when wet. I am hesitant to give anyway because the bars are so slimy after you use them. Do you have an experience with this? I think I used coconut oil and olive oil. Are homemade soap bars of pretty much the same texture as store bought or is the slimy-ness the norm?

    The HP soap sounds pretty much easy. Especially if I can use my regular crockpot and not have to get a separate one.

    Thanks for this post! I've been crocheting dish cloths and a bar of homemade soap would make a great gift to go along with the dishcloth.

  9. Oh, yeah....this is good. I have a couple of questions: Can anything be added to change the color? And, can this recipe be doubled?

  10. Carol.. if there is still lye left, you just cook it for a little longer.

    Gina, it sounds like it is a recipe issue. Not all recipes are the same.. but recipes high in olive oil can tend to be this way. Olive oil soap is the best for the skin so I guess there is a give and take in the situation.

    Anon.. You can add color when you had the fragrance oil (I like the natural look so I never color my soaps and forgot to mention that this could be added :).. the recipe can be doubled (and a bigger crockpot used).. BUT.. make sure you run the oil amounts through a lye calculator to verify the lye amounts.. they don't always necessarily double in a recipe..

  11. Thanks Crystal! I have made our soap for the last two years using the CP method. I am going to give this a try this weekend.

  12. This recipe has inspired me to give soap making a try. Where does one buy lye? I can't find it in the stores I usually buy from.

  13. Galleon.. I have a page on my website devoted to just that question (where to buy lye)..

  14. I have made two batches and they are going to be holiday gifts! Great recipe!

  15. Can you make any recipe into a crockpot recipe? Or does it have to be a hot process recipe? If so what is the difference in oils, and butters (if using) to lye?

  16. We purchase our lye from the local Amish stores ;)

    ~ Kerry

  17. I made a batch this morning and I'm wondering why my color is much darker than yours? I am a newbie at soap making but, this recipe doesn't have a lot of ingredients so I'm confused.

    1. Pam... the scent oil used can cause various shades to the soap.. and anything with vanilla will darken the color of the soap..

    2. I didn't use a scent. The soap has a fairly nice lather to it but, it's kind of crumbly.

    3. I'm not sure exactly why it would be crumbly... my first question would be.. are you sure your weight measurements were accurate? Also I've read over stirring could cause problems as well. Another issue could possibly be that when you put the soap in the mold, you did not pack it down firm enough..

    4. It's just slightly crumbly. I may have over stirred it. It was packed firmly.

  18. Just realized that fragrance oil was used in this recipe. Thanks for any help:)

    1. Yes.. and it was lemon scent which made the soap lighter in color as well..

  19. Can you use goat milk instead of water?

    1. Using milk is a little more tricky. If the temps get to hot the milk will scorch the milk and ruin the soap. I only make cold process soap with milk. And I freeze the milk first, measure it frozen and then add the lye to the frozen milk. This prevents it from scorching. I've never tried doing hot process with milk. So I'm not sure if the milk would get to hot or not.


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