The Secrets of How to Make Soap in a Slow Cooker

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Crock Pot Soap

Learn How to Make Soap in a Slow Cooker

When I first started learning how to make soap, somewhere in the back of my mind was the question: how can I speed up the curing process? Normally in cold process soap making, it takes 4-6 weeks for soap to fully cure. I’ve had a *few* batches that were ready in 2-3 weeks, but normally it takes longer. Then I found out about crock pot soap!

Basic Recipe for Crock Pot Soap

To start a good batch of crock pot soap, you don’t need to do anything special. That’s right, you can use any recipe for cold process soap. Crock pot soap is sometimes called hot process, different from cold process because it is heated and cooked for a while. If you want to use my basic recipe, there are no adjustments that need to be made. Start with the same ingredients and supplies.



  1. Find an old crock pot that can be designated for soap making. Be sure it is large enough so the soap has space to boil without spilling over. Many crock pots only have heating elements on the sides and not on the bottom, in which case you may need to double or triple this recipe to fill the slow cooker a little more.
  2. Pour the water into a quart canning jar. Slowly add the lye and stir until dissolved. Remember to wear long sleeves, use gloves, and wear a mask. The fumes that come from the lye will stop within a minute or so. (Read our response to the common question: Can You Make Soap Without Lye (Sodium Hydroxide)?)
  3. Next, measure your oils and place them in the crock pot. Be sure to measure them while in liquid form, not solid.  When the oils are hot (you can start on high to get it going, but then switch to low) you can add the lye. That’s right, I didn’t tell you what temperature they should be, because it really doesn’t matter with this process. If the oils are hot, the lye will be too and you’re going to cook it anyway.
  4. Once you get the lye and oil mixed together, stir by hand for 5 minutes. I honestly believe that this is very important as it brings all of the lye in contact with all of the oil. After 5 minutes, then use a stick blender to bring it to a light traceA light trace is more like pancake batter. Thick, but not like pudding. (This is different from cold process soap, in which the desired medium trace will look much like thick vanilla pudding.)
  5. Once it gets to a light trace, cover it and walk away. DON’T STIR IT! This was just about the hardest thing for me since I worry about it sticking. It won’t. After about 20 minutes, sometimes sooner, you’ll see some bubbling on the sides. Then it will start to boil (sort of) and turn translucent, almost like petroleum jelly. After approximately another 20 minutes, it will expand more and start to curl in on itself. You still don’t want to stir it yet. When it’s all translucent and has folded in enough to fill in the middle, then it’s done for now.

The Secret

This is the point where most instructions on the subject tell you to add your herbs and oils and pour it, but you can’t, because it’s all ropy, hard, and chunky. This is where my secret comes in.

  1. At this point, turn the heat off. Then add about ¼ cup water and mix it in. It’ll take some work, but it will eventually start to smooth out. (If you want to add powdered goat’s milk, mix about 2-3 tablespoons with about 2 tablespoons of oil [yes, oil, not water – water makes it lumpy] and add it before the water. The soap will probably turn orange or yellow and get really pasty, but adding the water after that will loosen it up.) You can add up to ½ cup water per batch and still get good results. If you add more than that, it will be easy to pour, but then your soap will be spongy and won’t set up properly.
  2. After it gets smoothed out, then you can add dried herbs and essential oils to make it what you want. Pour it into molds, cover with wax paper, and let it sit for 24 hours. Don’t worry about retaining the heat. You just cooked it all out!
  3. After 24 hours, take it out of the molds. (Cut it into bars if needed.) Set it on some parchment or wax paper to cure for a week or so and that’s it. The 4-6 weeks have been reduced to a week by cooking the lye out and speeding up the oxidization process. Sometimes it takes another week, but most of the time the soap is ready within a week.

Just one more note: Be sure to use an old crock pot. The lye will eventually etch the ceramic and it can break after a few years. Of course, I use mine a lot, so most should last longer. And for clean up, let everything cool and then add hot water and let it soak overnight. I use this water for my dishes or laundry. Rinse it and it’s good to go.

Have you ever made crock pot soap? If so, how did it go?


photo credit to heart hands home

About Debra Maslowski

Debra is a master gardener, a certified herbalist, a natural living instructor and more. She taught Matt and Betsy how to make soap so they decided to bring her on as a staff writer! Debra recently started an organic herb farm in the mountains of Western North Carolina. You can even purchase her handmade products on Amazon! Connect with Debra Maslowski on G+.

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  1. Sandy says

    hi 🙂
    I’ve been wanting to make my own soap but haven’t yet, This recipe looks like it’s easy and not scary. I want to try it out next weekend. I would like to make an oatmeal soap, as I have skin issues and oatmeal is soothing, how would you recommend tweaking the recipe to use it and still make it work? I saw your comment above but it didn’t say how much to add.
    thanks for any advice you can give!

    • P J Kielberg-McClenahan says

      I have made castile melt-and-pour soap with the addition of oatmeal, powdered ginger spice, and pure lanolin (available from Lorann Oils in 1 lb. jars) that is soothing to sensitive skin. The ginger spice gives it a slight fragrance, and the lanolin and oatmeal adds comfort and moisture to sensitive skin.

  2. Ellie says

    Can powdered lye be used to make soap? I can’t find anything else and I’m not sure if I should use it.

    • Tammy says

      Yes, lye comes in powdered/crystalized form. The important thing is that it is 100% sodium hydroxide.

  3. Jill says

    Thanks for these great tips! I want to add that each oil and fat requires a different amount of lye. Always use a lye calculator to ensure that your soap doesn’t turn out too caustic. Oils cannot be substituted for each other without adjusting the amount of lye accordingly. has an easy, free online calculator. Planning for 5 or 6 percent superfat will ensure some degree of moisturizing qualities and give you that little “cushion” of knowing that no lye remains in the soap once it’s processed.

  4. Rhoda Edwards says

    This soap recipe looks so simple that I am going to try it out. I have a fear about soap making, not of burning myself but of not getting the ingredients correct to cause the soap to form. Thanks for the cup measurement it makes it so much easier, and many thanks for the recipe.

  5. P J Kielberg-McClenahan says

    I have been using a crock pot for making glycerin, castile or goat’s milk melt and pour soap for some time. It works great for this type of soap-making.

    WARNING: If you are making lye soap, use a wooden spoon ONLY and DO NOT USE an aluminum crock pot! Lye, aluminum and water can create hydrogen gas, very flammable and dangerous! Only use ceramic or stoneware.

    • Debra Maslowski says

      Thanks for the info P J! I didn’t know they made aluminum crock pots, but yes, you should avoid them at all costs. I’ve never made a good batch of glycerin soap, but intend to try it now. And then next on my list is liquid soaps. I just got some potassium hydroxide and I’m itching to try it.

      • P J Kielberg-McClenahan says


        My aluminum crock pot was purchased several decades ago, probably most of them have been discarded by now. I have used it occasionally, but purchased a larger ceramic slow cooker and retired the aluminum one, until I tried it out as a melt-and-pour soap warmer. Glycerin soaps are very easy to create; you can add emollients, colors and scent, and have a wonderful product. Just be sure to wrap it up tightly, to preserve the fragrance.

  6. Mary says

    I make hot process in a crock pot when I make soap. I don’t have the patients to wait the 4-6 weeks to use it, that’s why I chose the hp method. I’m fairly new to soap making (since last July(2013)). My soap has always turned out well, but I couldn’t get it to look pretty like the cold process often does. Someone suggested I stop the cook at the gel stage. Well, I zap tested at that stage, and guess what? NO ZAP! It’s still not super easy decorate, but easier than before. Your right, it does take longer before you SHOULD use it (pretty moist) but you CAN use it if it passes the zap test. Just is a softer bar than if you let it cure longer.

    • Debra Maslowski says

      Thanks Mary! I’ve never heard of what I did called the “ZAP” test, but it makes sense. People at my classes invariably freak out when I do it, but I remind them that it’s safe and show them my tongue. It still looks the same as it did years ago.

    • Debra Maslowski says

      Sure you can Leriec, Just be sure to check one of the SAP charts to see what it’s closest to. Then you’ll be able to figure out how much to substitute for another oil.

  7. Tammy says

    At the end you mention that sometimes it takes an extra week, but that it’s usually ready within a week. I am brand new to soap making – with two batches of cold process less than a week into the curing stage. So, how does one *know* when the soap is ready to use?

    • Debra Maslowski says

      That’s easy Tammy! Just lick it! Ok, not literally, but touch the tip of your tongue to it. If it just tastes like soap, it’s ready. If there is a slight sting on your tongue, it’s not yet. I’ve been doing this since 1995 and my tongue is fine, though I really dislike the taste of soap. I keep water nearby to get rid of that taste.

      • Debra Maslowski says

        Yes, that’s true. All soap is made with lye. There is no substitute. If you are careful, you don’t need to b fear it. I did for a long time, but I got over it. I still get burns on occasion, but nothing serious because I’m careful. And keep the vinegar nearby in case you do get some on you.

      • JC says

        exactly! I tell people, no lye…no soap! period! now, if you want you could take the wood ash and make it yourself to be truly “natural” as they used to do before Red Devil came along. Lots more work intensive, but you will have a batch of real soap made with true labor of love!

  8. Carol Samsel says

    I use a crock pot for all of my soap making ♥♥♥♥ I will be trying the added water at the end to see how that works so I can do some of the fancy coloring methods. Thanks for sharing.

  9. jen says

    Thanks so much. This will be my first attempt at soapmaking, could I add a bit of oatmeal instead of herbs? I’m not sure if that would cook it and turn it mushy or not. Thanks!

    • Debra Maslowski says

      Yes Jen, you can. I add my oatmeal after I get the water part right after cooking the soap. I only use old fashioned oats because every time I use quick oats the soap gets slimy and has a terrible smell.

  10. Margaret H says

    I’ve made many batches of soap in the crockpot. I don’t like the smell of the soap while it’s cooking but the finished product is nice. I never tried your trick with water’s. But I will be sure go try it in the future.

    • Carol Samsel says

      I’ve made soap using lard and they come out fine…not as creamy as vegetable oils but they do work. Animal fats are what were traditionally used in soap making.

        • Debra Maslowski says

          I started out using animal fats instead of all vegetable as I do now. I only switched because I had so many people object to animal products. Lard makes a nice soft lather and a white bar. The bacon smell goes away after it’s saponified. I’ve also used tallow, chicken fat and buffalo fat. Didn’t like chicken, it went rancid. Buffalo was great, little smell and a nice hard bar with great lather.

    • Jaime says

      yes yes yes beef tallow makes the best and have read that it mimics your own skin. makes a very silky feeling bar of soap.

  11. Erin says

    Help! My daughters both have terrible exec a and I have been toying with making my own soap so it will be gentler on their skin. But my oldest is allergic to coconut, what can I use in its place? Thanks!

    • Carol Samsel says

      I’ve made soap with this method for years using olive oil and caster oil and love it. You can google for recipes…just be sue to run all recipes through a lye calculator to make sure you are using the correct amount of lye .

    • Jaime says

      Just use all olive oil and it will work great but after the cook time add 2 to 3 oz of raw shea butter it is great for healing the skin and so is the olive oil. Hope that helps good luck making soap it does get eaiser and I love it and usually do all hot process but have not added water at the end to smooth the soap out.

  12. Kristi ~ Hippie Chick Herbal Harmony says

    Great advice! I love the hot process, but when it comes time to add my “goodies”, the soap is always so hard to work with. I thought about adding water, but was afraid it would mess up my batch. This should help me swirl and blend better.
    I’m assuming by doubling the batch, I should also double the water after the cook.
    Think I’ll give this a try today!

    • Debra Maslowski says

      Hi Kristi! I’ve done both double the water and using just a bit more. It just depends on how much your soap has cooked down. And when I add powdered goat’s milk at the end, it gets really pasty, so I have to add more. The soap stays softer for a week or so, but then hardens up nicely. And I haven’t seen much shrinkage.

  13. Michele says

    I love hot process. My trick always involves playing with water amounts. Even in cold process, saponification is usually complete within 48 hours. My cold process bars are hard as a rock and ready to use within that time, because I don’t overdo water. All I eliminate is the curing process to release the water to make the bars hard enough. I use slightly more water with hot process because the bars are cooked to ‘done’ right away. I love soap making. It’s like my fudge making addiction, only less calories! thanks for the tips!

    • Sarah says

      Michelle, I am new at making soap. I am wondering if there is a cheaper way you have found to fragrance your soap. I like the essential oils but have found that you really do use a lot of that in one 2 lb. Batch. Any suggestions??

    • Debra Maslowski says

      Thanks, Michele! I’ve used most of my soap right away too, but some do take longer, so I usually tell people to wait. There is a lot of talk going on about water reduction and in the batches I’ve tried it with, it seems to be ready faster. Thanks for pointing that out.

  14. Monique says

    My very first batch of soap was hot process in the crock pot. We used it as toothpaste. It was easy!

  15. angelina says

    I would just like to add that this is a brilliant idea, just one thing though, instead of saying a 1/4 cup of lye, use a proper weighed amount using an online soap calculator like mountain sage. Lye needs to be properly calculated to make sure that after all your hard work you have a soap that is creamy and moisturizing and not harsh on you skin.
    Thank you for posting this
    angelina x

    • Debra Maslowski says

      That’s true, Angelina, for most recipes. However, I have come up with a recipe that uses cups, not ounces. I’ve already calculated the ounces and it’s the same every time if you follow these instructions. You can see the full recipe and instructions in the soap making article I did here a few weeks ago. For all other recipes, you would want to use a scale.

      • JC says

        as you can see by my blog name I am not one to be picky about measuring. I wing it! I have a fabulous recipe that gives in pounds for the fat & oz for the lye. I have always gotten soap not always pretty, but functional & rarely a fail! It needs little attention and I like it that way. I am eager to try this method however & will enjoy the smaller batch. My recipe gives me a year or more worth of body soap (when all the kids were still at home) with plenty for giving as gifts. Thanks for this new idea~

      • Ratna says

        Lye is not standard around the world. A cup of lye crystals from India weighs considerably less — i.e., there is less sodium hydroxide — than commercially packaged lye crystals in the US and Europe. I think the commenter who suggested that you include a weight is being wise.

  16. Dianne Finnegan says

    Thanks so much for this! I have been making cold process for just about 4 months and the last time I tried to make soap in a crock pot, well, lets just say I tossed it all in the trash. I look forward to making this soon. It will be nice to have a bar of soap that doesn’t have to sit around the house for weeks before I can use it!!

    • Debra Maslowski says

      Thanks Dianne! Like you, I was fed up with waiting and/or having soap that looked like it had been stretched out and shoved back together like taffy. It took me a few years, but I finally learned. Now that I have, I may never go back to cold process.