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!

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  1. Misty says

    Ok, this will be my first time ever making soap of any kind. I’m wondering why the emulsion blender isn’t used at the end to blend it all back up instead of hand mixing with water? I’m sorry if this is a repeat question.

    • Debra Maslowski says

      No worries about repeat questions Misty. I’ll take them all! I don’t use a stick blender at the end because the mixture is so thick that the blender wouldn’t get through it. If you add more water, it may work, but then there will be a lot of shrinkage in your soap later. You can try it if your soap seems thin enough, just be careful not to make a lot of suds as you work it.

  2. Sheryl Brazier says

    I read somewhere to spray the molds before pouring the soap. I was curious to know what do you use to spray them with

    • Debra Maslowski says

      I don’t usually spray my molds, Sheryl, unless they have intricate designs. Then I use a spray on oil. You can get it at the grocery store, or you can buy a mister and use any oil in it. I use olive oil since it’s already in the recipe. After spraying, tap the mold a few times to get rid of any bubbles. If there’s too much oil and it leaks, just dab it with a paper towel.

  3. Audrey says

    My crock pot soap turned out orangish-brown. Is this normal? Will it possibly lighten after it is finished? If not, would you know what I did incorrectly?


    • Debra Maslowski says

      Without seeing it Audrey, I can’t say for sure what might have happened. If you used powdered milk, milk will sometimes turn orange or brownish as the sugars heat and caramelize. This is totally normal. It doesn’t happen every time, just sometimes. It may have to do with the heat, I’m not sure. If you didn’t add milk, it could have to do with the oils used. Some oils turn the soap darker than others. Usually, the color will fade over time.

    • Debra Maslowski says

      The coconut is used as a base oil, Nirit, not as a butter. Coconut butter is a different thing, not at all like shea or cocoa butter. You can use cocoa or shea butter as an added moisturizer. Add it at the same time as the essential or fragrance oils. Because the soap is hot at this time, you don’t need to melt it first. A few tablespoons should be fine.

    • JC says

      yep! get a big stainless steel pot, put your fat & rain water in, add the lye and stir as often as you can (yes it will be hard, but slowly softens & gets easier, keep stirring to incorporate fat with lye & water) for 48 hours. Wearing all the protection garb of course. Goggles, gloves, long sleeve shirt, face mask or bandanna to cover mouth & nose. Lye is dangerous!

      Only use a wood spoon for stirring. A really long spoon is ideal.

      At the end of 48 hours, heat on low to melt completely, add any “smelly’s” you desire and pour into a greased or wet cheese cloth mold, leave it to sit till hard, 24 hours or longer. Cut & wait for six weeks to cure some place out of the way. Lightly covered with a cloth to keep dust off.

      Lard or tallow are highly recommended for this recipe.

      Crisco, before it was made from soy & other nasties was my best soap fat. The bleaching and such are not favorable to put on ones skin though.

      Regarding lye. If your Publix grocery store still sells Red Devil Lye, go to a register and get a plastic bag. Use the bag as your glove to pick up can of lye and wrap in the bag. Remind the cashier to not touch the can or they will be itching & burning just from touching the can. Then I have cashier put in paper bag. Keep the can in the bags till ready to use. Use rubber gloves to handle can of lye while making soap.

      EXTREME CAUTION always with lye. goggles. gloves. face mask. long sleeves. Did I say Lye is dangerous? NO CHILDREN OR PETS around soap making or this lye!

      5 lbs fat
      1 (13 oz) can red devil lye (no blue crystals!)
      6 quarts cold water (distilled, rain, spring or well)
      3 TBSP borax
      Mix all as mentioned above.

      On molds~ I have used pvc pipe, cardboard box, shoe box, glass square pan, bread pan lined with freezer wrap (not ideal). Sky is the limit. Get creative.

  4. JC says

    for the newbies to soap making..if the batch fails, shred it and do laundry. A little goes a long way, so be careful. It is never a loss. Don’t toss. It can always do something useful~ be creative!

  5. Nerissa says

    Thank you for posting this, I’m excited to try your recipe this week…one question when you recommend using the emersion blender…once its used on soap can I use it on food again?

  6. Kathleen says

    I tried this recipe as my first attempt at soap making, but I didn’t fair too well. It came out spongey as was stated if too much water was added. The only problem I had was that I kept letting it set in the crockpot (NOT stirring) but then when I started the stirring process it acme REALLY stiff and I couldn’t work it out without more water.
    Is there a way to salvage this recipe and make it a liquid soap, and try the recipe again? Maybe my crockpot was running too hot? Mine is an OLD one from the ’80’s that has a BASE heating element. Not the drop in kind that is all you find now.
    Any help would be appreciated. I hate to waste that much material.
    Thank you,

  7. Tammy says

    Made my first batch of crock pot soap tonight, and have I got a beginner’s tale to tell…
    I used an old 6-quart crock pot and a total of 3 lbs. of oil (half rendered bacon grease and half coconut oil). A word to the wise: NEVER make soap in a 6-qt. crock pot using 3 lbs. of oil. I think it is going to be okay once it has cooled off, but I am sure that the final consistency was a considerably different than it should have been.
    I had to rescue the soap from spilling out over the lip of the pot. This eventually entailed taking the lid off because the mixture had bubbled up so high that it was lifting one edge of the lid up and pouring out that side, but the weight of the lid was not allowing the soap to go through it’s rolling motion in the rest of the pot. I ended up cooking it about twice as long as recommended because, after having taken the lid off, it just didn’t seem to be doing what it was supposed to do.
    There was no pouring of this soap even after adding the maximum amount of water and goodly amount of rosemary EO. I scooped it out and spread it into the molds. It reminded me of a cross between mashed potatoes and super thick fudge. Something tells me that this soap will be ready for use in considerably less than a week.

    • Tammy says

      Update: The soap is a little softer than my cold process soaps have been, but other than that, it is fine. Lathers nicely and leaves us feeling clean. It smells a little odd, but I think that is from the bacon grease. I think I’ll keep it in cold storage. There is probably enough there to last us a year, though I expect a few male family members may be getting some as gifts this year. It will be perfect for those outdoor-loving guys who are so hard to buy for!

  8. Nadia says

    Hi there – I have never made soap before, but I am an avid crock-pot user. The only “personal care” item I have made is deodorant…so making soap is a big step! 🙂

    My question is really about the crockpot. You mention that the lye will be hard on the crock pot. Does that mean I shouldn’t use my crockpot for cooking foods if I decide to use it to make soap? In other words, should I have a separate crock pot for making soap? (this might mean I go shopping for a new crockpot for food…)

    Many thanks in advance for your answer.

  9. Holly Fearnow says

    I just cooked up a batch last night. I used EVOO instead of regular olive oil because that’s what i had on handl. It almost seems a bit to oily, but then again it was my very first time making soap. As the bars cure, do they get less oily? Or is it because i used EVOO instead of regular olive oil?

    • Debra Maslowski says

      Usually the bards just harden more, Holly, but they don’t get less oily. It may have been the type of oil. I only use the cheaper olive oil because it’s not for cooking and it doesn’t need to be that pure. The soap just seems to turn out better. One common problem with this recipe is that people are afraid of the lye and tend to not fill the measuring cup all the way, or they use the wrong type of measuring cup. You need to use a dry measuring cup, not one meant for liquids. Either way, it looks like you had too much oil and/or not enough lye. There’s nothing you can do now to change it. I would let it sit a week or so and if nothing else, dissolve it in a bucket of warm water and use it to get rid of pests on your plants. I use a tablespoon or so in a spray bottle of water and mix it well. Then go spray it on aphids or spider mites. It will eventually start to smell rancid due to the excess oil. That’s when it’s time to get rid of it. Well diluted, it can be dumped down the drain.

  10. DeAnne says

    I too am wondering how much essential oil must go in to be able to smell it later. Never made soap before – what do you use as a mold?

    • Debra Maslowski says

      Hi De Anne! Another tricky question about the molds. You can use just about any kind of plastic as long as it has some give. I started with plastic shoe boxes. It made a large bar that would be cut after the first 23 hours. Then I went to smaller molds, but they lost the heat too quickly. I solved this by layering them in a cooler with sheets of cardboard in between. One client wanted round bars, so I made molds with PVC tubes. Use the thin wall, it’s easier to work with. Now I use almost anything I can find. Yogurt containers are my new favorite.

  11. joni says

    I was wondering about the ratio for adding dried herbs and/or essential oils? can I add as I like or is there a measurement I should try to follow in order to get a nice mix?

    • Debra Maslowski says

      There’s no good way to measure the amount of herbs and oils, Joni. You have to start slow and add more if you like. I’ve made the mistake of adding too much plant material and not having enough soap around it. It crumbles and falls apart. The oils are another thing you have to do by choice. I wouldn’t go over 5% of the total volume. I once dumped a half a bottle of peppermint oil in my soap accidentally. It was nearly unusable for the oil leaching out of it!

      • brittany says

        Hi Debra,
        I want to make soap with using peppermint essential oil…what herb would you recommend with this? I definitely like a little texture in my soap?

  12. Darinka says

    Great recipe Debra, thank you. Question, have you ever tried adding a hydrosol at the end instead of the water?
    I’ve done this with a few batches and it’s wonderful because it adds even more benefits to the soap not to mention added aroma. I’ve done Rose, Neroli and Lavender. I am about to make a Neem, Carrot & Goat milk recipe and I am hoping by adding neroli and rosemary water, it will help mask the smell even further. Wish me luck.

    • Debra Maslowski says

      Thanks Darinka! I’d nearly forgotten about hydrosols. Yes, I have used them, though they tend to lose some scent and color. I love rose water, and even though the lye seems to destroy the scent and color, the wonderful skin softening ability is still there. I’ve also used infused oils, like calendula, as part of the oil used. It works great this way too.

  13. Nita says

    I have never done cold or hot. But so want to try this!! Where do I get the herbs to put into my soap? and can a newby do this? Thanks

    • Debra Maslowski says

      Hi Nita, yes, this is geared towards newbies in the soap making world. I’ve made the instructions very easy so anyone can do it. I get most of my herbs from my garden. I always dry them first as the lye can rot fresh plant material and they can also add too much moisture. You can buy dried herbs at the grocery store (go for the bulk section as they are generally fresher there), a local food co-op or online. When I can’t get something locally or I need a lot, I go to reputable sources online such as Brambleberry or Majestic Mountain Sage.

  14. Natalie says

    Thanks for sharing your tips and a great recipe! I love the simplicity of this and want to attempt soap-making. Do you think it would work if I used rice bran oil instead of olive oil (allergic) and used the same exact amounts of it and everything else? I have read that rice bran oil can be substituted for olive oil, I just don’t know if it changes anything in the recipe.

    • Debra Maslowski says

      Hi Natalie, Yes, you can but the quality of the soap may differ due to fatty acid chains, lipids and so forth. The SAP value is very near the same, so the amount of lye you use wouldn’t change. Your soap may be harder or softer, so you may need to experiment. There is a great SAP chart at From Nature With Love.

  15. Phallin @ CottageHomestead says

    I was wondering if the same measurements consist for the lye if you use the lye beads instead of flakes? Also when you add the water at the end, what do you mix it in with….the stick blender or just a spoon? Thank you!

    • Debra Maslowski says

      I’m not sure where you are from, Phallin, but around here all the lye I’ve seen is in beads. Or possibly powdered. The flakes are usually potassium hydroxide, which is used for making liquid soaps. They are NOT interchangeable. If you are sure you have 100% sodium hydroxide, then I would weigh it and use a recipe that calls for weights. Then you can be sure you’ll have the right amount.
      As for adding the water at the end, I use a spoon. It’s usually too thick to get a stick blender into. It takes a bit to get it worked in, but it’s well worth it.

  16. Judy says

    Hi Debra,
    I am brand new to soap making. I want to try your recipe for making soap in the crock pot but I know I will want to add some essential oil for fragrance. Since this will be my very first time to make soap can you tell me how much essential oil is needed so it’s noticeable?

    • Debra Maslowski says

      This is always the hardest question to answer, Judy. It depends a lot on your nose, what kind of oil, the strength of the oil and the quality. I generally say start with 10 drops or so and add from there. Be sure to sniff coffee in between whiffs to clear out your sinuses. And remember, you can always add more, but once it’s in there, you can’t take it out!

  17. Darcy says

    Could you just put in goat milk instead of water and the powdered goat milk? I’m assuming that just like with other soap making that you want a crock pot and other utensils just for soap making and not used with food, right?

    • P J Kielberg-McClenahan says

      I hope we are talking about the same thing. “Melt and Pour” refers to soap made with meltable soap bases made of either glycerin, goat’s milk, castile soap, or olive oil based soap. No lye is required with the above soap bases, all that is needed is fragrance, color, emollients and any additive such as spices or oatmeal, etc.

      The cold-frame method requires lye, etc., and either requires a long “curing” time or the newer crock-pot method, as mentioned above.

      I have posted this to just make sure anyone reading understands about the methods, and that each one should be from a recipe especially tailored to the products being used.

      • P J Kielberg-McClenahan says

        Also, I get my “melt-and-pour” soap bases from Glory Bee Foods. They have a wonderful website with all natural products perfect for this type of soap making. Their prices are the most reasonable I have found, also.

        • Debra Maslowski says

          Thanks for clarifying that P J. Glycerin soap, or melt and pour, is an end product of cold or hot process. You need to add alcohol and sugar to clarify it and I’ve never been successful at that. I buy from great sources like Glory bee, Brambleberry or others that have it already done.

    • Debra Maslowski says

      If you’re making cold process soap, Darcy, you can start with goat’s milk, but it’s a long and involved process. I’m still working on perfecting it, so I can’t really give advise there until I do. That’s why I use the powdered milk at the trace, or add it to the melt and pour soap. Or, even easier, get the melt and pour base that has it already in it.