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 with our cold process recipe of water, lye, and fat. This recipe is great for making 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 the 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 the 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 for your crock pot soap 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 crock pot soap 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.

Turn Off the Heat

  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 the crock pot soap 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. Lisa says


    Thank you for this awesome idea. I can’t wait to try it!

    I have a couple of questions.

    I’m assuming this changes the properties of the ingredients since it is the heat process method? Can you substitute hard butters for the oils? Is the heat transfer method possible for this? I’m a newbie to cold process but not MP so I apologize for all of the questions.



  2. Mouse says

    There are so many pop-ups on this page that by the time I got done scrolling through all the ads I didn’t care anymore.

  3. Victoria says

    Help! I have made cold process soap using vegetable oils for many years. I tried the crock pot method. I measured using a scale and used a soap calculator. The soap cooked about an hour or so, and set up as pictured. Last night I cut it, and today I wrapped the bars in tissue paper. I did the zap test, and no zap. I then, just to see, tried a Ph strip. The strip showed high alkaline. I am sure if I age it, it should be fine, but, what did i do wrong?

  4. Katura Carter says

    I have a question. What size slow cooker did you use for this recipe? 5qt, 7qt? I’d really like to know so my first batch doesn’t end up a disaster. Also, after I finish the first batch, can I clean up immediately and start on another batch the same day without waiting overnight?

    • Debra Maslowski says

      The size of the crock pot only matters if you’re making larger batches Katura. I like to use my 8 quart with a triple size batch. It has a removable crock which makes clean up easier. Two things to remember-first, most crock pots only have heating elements on the sides so as not to damage the counter top when cooking. Smaller batches of soap may not go up high enough in the pot to properly cook. Then second, be very careful of overflows. I had my liquid soap overflow the pot and it damaged the cord. I didn’t know the lye had eaten through the plastic until I got zapped while cleaning it. Best course of action there is to unplug it before cleaning!

      • Katura Carter says

        Thank you for the response! How many bars of soap will this batch be if I used a standard soap mold? This will be my first time doing this and I’d like to not have anything left over. 🙂

        Also, can I clean up immediately and start on another batch?

  5. brittany says

    The step when or if you decide to add goats milk what kind of oil do you mix with it? does it matter or can it be any kind of oil?

    • Debra Maslowski says

      It can really be any kind of oil Brittany. I try not to use a solid oil, like coconut, because if the soap is cooler than the melted oil, it may solidify back on contact. Some of my favorites are sunflower and safflower for the vitamin E content and grape seed for the antioxidants.