Making Hot Process Soap in a Crock Pot

by Daisy on 09/25/2008

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bar of hot process lye soapHave you ever wanted to make your own soap? It’s a good time. I love it and make soap several times a year.

The reasons I make my own soap:

  • After I started to use homemade soap, every other soap seemed so artificially-fragranced and I came to dislike how the fake scent from the lab-produced fragrance oil lingered uncomfortably on my skin
  • Homemade soap has become my favorite small gift, either by itself or as part of a gift basket; people really seem to appreciate it and are amazed that you made it yourself
  • I love watching the ingredients come together and turn into something special. It’s chemistry, but it seems like magic
  • I love customizing base oils and essential oils to make special-purpose soaps
  • I love how homemade soap smells, even before I add essential oils
  • It’s really fun!

In this tutorial I’m going to show you how to make a type of soap called Hot Process Method Soap in a crock pot. I’m going to demonstrate the basic procedure, then at the bottom of the post I include a basic soap recipe to try, including a variation to make a Honey and Oatmeal version which is slightly more advanced.

The advantage of hot process is your soap is ready almost immediately, rather than having to wait a month or more before you can use Cold Process soap.

Making soap can seem very intimidating at first, but it really is doable once you have the right equipment and follow some simple safety rules.

Simple Soap Safety In a Nutshell:

  • Wear old, long-sleeved, leg-covering clothes and perhaps an old apron to cover your skin and protect you from splatters
  • Wear rubber gloves
  • Wear safety glasses
  • Maintain good ventilation (your stovetop vent hood, a small fan, or an open window is good)
  • Keep small children and pets out of the area while soaping
  • Set up your equipment and supplies before you start and read all instructions before you begin
Get your equipment ready

Get your equipment ready


  • scale (digital is nice but not essential, check overstock stores for deals)
  • immersion/stick blender
  • crock pot/slow cooker (I got mine at Goodwill on the cheap to use exclusively for soap making)
  • large non-aluminum bowl or pitcher (can be hard plastic)
  • long-handled plastic spoon
  • old newspaper soap mold (can be an empty Pringles can, a washed milk carton, or special soap molds from the craft and hobby store)

If you can’t find these secondhand, try these alternatives I selected for a balance of good reviews and low cost:


  • Oils of choice (I commonly use olive oil, coconut oil, and castor oil)
  • lye (I use 100% sodium hydroxide drain cleaner granules from the hardware store or I buy it online)
  • essential oil, optional
  • water


weighing oil for soap

Weigh your oils.

Place in cold crock pot.

Turn heat on low and allow to melt if necessary (coconut is solid above ~70 deg.)

Measure water and pour into pitcher or non-aluminum bowl.

weighing the lye for soap

Weigh lye

add lye to water

Add lye to water and stir gently to dissolve (l like to set the bowl in the sink before I add the lye and do my pouring and mixing in the sink)

REMEMBER: Always pour the lye into the water, not the other way around or you can have a volcano. Mnemonic device–remember ‘snow falling on a lake’ is the right way. Don’t stick your head over the lye mixture during or after the add–avert your face because it can gives off fumes

Allow the lye water to cool for a few minutes so it’s not super hot (combining the lye and water produces heat).

add lye water to oils

Then pour the lye water into the oils in the crock pot and give it a gentle stir.

The immersion blender goes carefully into the lye water+oil

The immersion blender goes carefully into the lye water+oil

Plug in your immersion blender and lower it to the bottom of the crock pot into the oil mixture, holding the blender at a slight angle so it doesn’t suck itself to the bottom of the pot, but also making sure it is fully immersed in the solution to minimize splatter.

slowly rotate the blender around the bottom of the pot until it reaches trace

slowly rotate the blender around the bottom of the pot until it reaches trace

Turn on the blender and gently stir.

a pretty thick trace--it doesn't have to get this thick to be ready

a pretty thick trace–it doesn’t have to get this thick to be ready

Stir until you reach the slightly mysterious point known as “trace.” All that means is the mixture will be pudding-y enough so that stirring leaves a faint trail as you move the blender or a spoon through the mixture.

Cover and wait

Cover and wait

Remove the immersion blender, unplug it, rinse it, and set it aside. Put the lid on the crock pot and let it heat up (still on low setting) until the sides begin to pull away and it starts to look like something interesting is happening.

see the darker part underneath?

see the darker part underneath?

This will take several minutes depending on the volume of your oils and the heat of your crock pot.

the sides begin to change

the sides begin to change

Using your spoon, stir the mixture down, scraping the bottom and sides. Allow to cook for an additional 20 minutes or so (times can be inexact), stirring frequently at the beginning and constantly toward the end of the cook.

completely bubbled top

completely bubbled top

Don’t leave your soap.

the texture has transformed completely

the texture has transformed completely

It will begin to start to look like applesauce and become a bit waxy-looking.

Continue stirring until it begins to darken and become more opaque and waxy. How to know when it’s done: I let a tiny dab of the soap cool on the end of my spoon and touch it with the tip of my tongue to see if the soap “zaps” like a 9-volt battery. If it doesn’t zap, it’s ready to put into the molds. If it zaps, it needs to cook some more. Continue cooking and stirring. It may “rise” and “fall” again as it completes the saponification (turning into soap) process.

stir it in quickly before it begins to cool!

stir it in quickly before it begins to cool!

Once it is zap-free, quickly stir in your essentials oil(s) and spoon the soap into the mold or molds.

smooth it out quickly because it hardens fast

smooth it out quickly because it hardens fast

It may look quite amber at this point; it will lighten up as it cools. After several hours or overnight, the soap should be cool throughout and hard enough to unmold and slice.

slice it as thick or as thin as you prefer

slice it as thick or as thin as you prefer

Technically the soap at this point is ready to be used, but it will improve and harden with a couple of weeks curing time.

the ways to package soap are unlimited

the ways to package soap are unlimited

After it’s cured, package it up and keep it on hand for gift-giving and your own use. I like to print out labels I make up with the type of soap and ingredients.  The sky’s the limit in terms of presentation. Simple craft paper, paper bags, cellophane treat bags, baker’s twine, sisal, ribbon or fabric make great soap adornment.

You can use any soap recipe for hot process soap, including recipes for cold process soap. However, I’d stay away from recipes that call for lots of additions like dairy or texture, especially at first. Hot process is hot and those things can increase the likelihood of scorched soap.

Here’s one of my favorite soap recipes, one I included in our book, which, incidentally, has a great section (if I say so myself) on soapmaking and four of our favorite recipes for soap, as well as lots of other homemade goodies that go great in a gift basket with soap.

Basic Soap Recipe

36 oz. olive oil (emollient and gentle)

6 oz. coconut oil (helps make a good hard bar)

3 oz. castor oil (improves suds)

6 oz. lye

12 oz. water

2-4 oz. essential oil of choice, optional

Follow procedures above. Also good made with the Cold Process Method.

For the Honey and Oatmeal version, add 3 Tablespoons of honey as soon as the soap has passed the zap test (at the point when you would be adding the essential oils). Turn off the crock pot and stir in a mixture of 3 Tablespoons of oatflour and 3 Tablespoons water. Stir well and mold as usual.

brown paper sealed with glue stick makes an easy, biodegradable packaging

brown paper sealed with glue stick makes an easy, biodegradable packaging

I hope you give it a try, you’ll love it!


{ 37 comments… read them below or add one }

Daisy July 24, 2012 at 11:10 am

Katrianna–You could do a small batch. Just make sure there is enough room for the total measure of your ingredients plus room for it to puff up and be easy to stir without going over.

Paget Cosper August 18, 2012 at 12:19 pm

I love your recipe just wondering could I bother you for a more exacact copy of it IE….. X amount of oilver oil…. thanks I will def. make this for christmas

Daisy August 18, 2012 at 8:24 pm
Kim October 15, 2012 at 12:19 pm

I just made the oat n honey Castile crock pot recipe. I notice there are little “spots
Which look like might be spots of honey. I’m wondering if I need to rebatch this.
Thanks, kim

Daisy October 15, 2012 at 2:08 pm

Kim–I don’t know. Maybe give it some more time and then see.

Ruth M. Grant-Couch December 8, 2012 at 5:22 pm

I am enterested in making soap. I just ran on to this today. I am looking for the clear like soap with glycerine in it.

deborah January 12, 2013 at 11:24 am

I made this for the first time today and I had white foam on the bottom and sides. After an hour I still didnt have separation phase. I used a recipe with 80% olive oil, 20% coconut oil and lye/water using the lye calculator. I got a lot of soap flakes also. What did I do wrong?

Daisy January 12, 2013 at 3:22 pm

deborah–I am an admitted newbie in terms of hot process. You may have done nothing wrong and merely caught the soap fairies on a day when they were in the mood for mischief. Try the experts over at and they will probably have some intelligent advice (as opposed to mine)!

Elaine March 9, 2013 at 1:54 pm

Love the tutorial!! I’ve been making hp crock-pot soap for years and won’t use any other soap. I used to use the double boiler and double batch the soap. Now I think cp-hp soap is easier and use different additives before molding.

Thanks, for sharing.

Val March 18, 2013 at 3:36 am

Hi. I am just after hot processing a soap with high olive oil content. I cooked it for nearly 1 hour before moulding because it was very oily. I have moulded it and cut it and it seems to have ‘dried’ some. I think I will let it sit for a few weeks and see if it cures out. I checked my lye content and it was correct. What could have happened?
I love your website.

Daisy March 18, 2013 at 6:07 am

Val–Thank you! I wish I could help, but there are so many variables it could be. I’ve been thinking, lately, about news reports that say a lot of the olive oil sold really isn’t what it says it is, so there’s another variable to think about! Maybe it will reabsorb with time. Fingers crossed!

deborah March 18, 2013 at 4:45 pm

It sounds like she did the same thing I did. Overcooked because I wasn’t getting that jelled look. I did a rebatch (put all back in crockpot and added some water) once it was all melted and clearish, I quickly repoured into the mold and didn’t mess around with it. It came out perfectly! When I sliced it, it was like cheese and didn’t crumble like my first attempt. I think there is a tendency to overcook the first time to make sure the lye has neutralized.

Sherry Giannini November 11, 2013 at 8:43 am

Is there any way to make this without the Lye?

Daisy November 11, 2013 at 9:16 am

Sherry Giannini–Sorry, there is no way to make this without lye. If you want to “make” soap without lye, you will have to go the melt-and-pour route. That is a product which is basically bulk soap which you can melt and then to which you can add smells and other additives and then pour it into molds, sold in hobby stores and online soaping supply stores.

april November 11, 2013 at 9:36 am

This recipe has far too much water for the amount of lye and oils. No wonder it takes so long to cure! Given that amount of lye I would have only used 9 oz water. HP recipes and CP recipes should different in liquid…most lye calculators don’t take that into account, hence I don’t use them!.

Desiree November 11, 2013 at 1:56 pm

Could I use a different oil such as coconut, almond or argan oils. And what exactly is ” melt and pour route” I was thinking the same thing as the other person. I thought lye wasn’t good for your skin?

M November 11, 2013 at 2:02 pm

Why do some soaps have saponified oils as the ingredients? Is this lye already mixed in with the oils?
Is there a place to purchase saponified oils?

Daisy November 12, 2013 at 8:47 am

M–Naw, saponified oils is just a fancy way to say “soap.” If they say that, and don’t say “lye”, they’ve just managed to convey that they used lye without saying the word itself. Does that make sense?

april November 12, 2013 at 8:47 am

Melt and Pour is a glycerin soap that artisans melt first, then pour into various molds for use. Sometimes they add scents, colors, oils, etc…but the M&P product is ready for use when they get it. Cold process or hot process soap making involves taking pure fats, adding lye, allowing for the chemical process of saponification, and voila you have soap. SOAP of any sort has lye in it, that is what makes it soap. And yes, too much lye, lye that hasn’t completed the chemical process, that can hurt your skin (burn)…proper soap making and time makes sure there is no lye left in the batch.

Daisy November 12, 2013 at 8:51 am

Desiree–You can use different oils, just put them in a lye calculator like this one: MMS to get your adjusted lye and water amounts. Lye is certainly caustic on it’s own, but once it is blended with water and mixed into oils in the right proportions and allowed to cure, it is, simply, just soap, and is what we’ve always known and experienced as soap. It’s the only way to do it!

Daisy November 12, 2013 at 9:13 am

april–Yes, I’m much more of a cold process gal. Good to know to adjust the water down.

Annette December 1, 2013 at 6:50 pm

I made this soap several months ago. While it was very easy and straightforward, my skin did not like it. I gave lots of it away, and everyone I gave it to LOVED it. Fast forward about 2 or 3 months…I was out of soap. I grabbed a bar, and lo and behold, it was fine. Lesson learned: if it isn’t working, let it age. I will be making another batch to age for a while this week.

Thank you for a great link!

Rere December 8, 2013 at 2:15 pm

Great recipe! But to me kind of complicated.

Sherie January 5, 2014 at 5:12 pm

where do you buy lye?

Daisy January 6, 2014 at 6:22 am

Sherie–You can get it online from soaping suppliers, but I usually find Roebic drain cleaner at Lowe’s (check that the package says 100% sodium hydroxide).

D February 1, 2014 at 1:51 pm

castile is just olive oil. Bastile is the combined oils version. 🙂

Nicole H May 13, 2014 at 10:42 pm

Deanna I have enjoyed reading your post!! I have dibbled in soap making off and on for 3 years. I enjoy the process. I also own a small business (Global Spice Exchange) specializing in natural products for artisans who make their own products. I am contemplating adding a blog to my website and would love your permission to include this post for novice soap makers. I invite you to browse my site at your leisure if needed to base your decision.

Daisy May 14, 2014 at 6:12 am

Nicole–Thank you. Sure, we welcome folks to put brief intros with a link to one of our posts on their site. Obviously the post in its entirety with no attribution isn’t cool, which I’m sure you know (but you wouldn’t believe what happens sometimes!) 🙂

gail schwartz July 25, 2014 at 4:18 pm

Hi, I need help! I made a triple batch of hot process soap yesterday. I have used the same recipe with success prior but holy cow something has gone horribly wrong. I looks like curdled cheese and it has oil sitting on top. What did I do? Can it be fixed???

Jester August 1, 2014 at 7:50 pm

Sorry but Castille is ONLY olive oil, please stop spreading misinformation so the real soapers out there will no longer have to keep straightening out this crap. Pure oil soaps are NOT Castille, 100% olive ONLY as this is the recipe originally from Castille.

Christy August 8, 2014 at 11:00 am

I am excited to add honey to my crock pot soap. Great job! You can check if it is done by touching the soap to the tip of your tongue. If it tingles it is not ready. 🙂 mine usually takes 14 hourish. I have left it for 24 out of laziness and it was fine. Seemed to lather better. COuld have just been that batch. Who knows. Where does everyone buy their lye? It is expensive here and I have to search it out at farm stores. I am in Columbus Ga.

dana December 25, 2014 at 9:05 am

looks great, but it isn’t “castile”. 100% olive oil is castile.

daniel boza March 1, 2015 at 3:20 pm

Hi thanks for sharing, i can translate it to spanish and post in my blog or in youtube channel, ill say u are a author or original font.. bye

Jackie March 19, 2015 at 6:07 pm

Hey Gals–
Been making soap for 17 years. Been earning my living for 15 years with my soaps.

That separation phase only happens every once in a great while. The soap is not done at this point, it is only starting to cook. If this happens, you should put the stick blender back in and get it back to trace. (BTW and plastic things that come into contact with the lye are contaminated and should not be used for food again. The soap will rise up several times–the process takes about 45 minutes for an average size batch. When the soap is done cooking, it looks like really thick mashed Yukon Gold potatoes, it starts sticking to the sides and it quits rising up out of the crock.

The soap at the point you showed first going into the mold is not soap at all–just a blend of oils and lye…in other words…not safe to use and it will burn and scar you if you are not careful. If you cook to the point that the soap is “done”, you then let it cool down to about 140 degrees and then add you scent and other additives. I let mine cure about two weeks to harden up. But once it is done, you can take a small dot of the soap out and try it. Castile soaps (100% olive oil) do not lather, they have a small foamy lather and are VERY moisturizing. On my skin that means almost slimy. But in this recipe with the addition of the castor you should have a bit of lather. Also, while the bar of soap is very hard, that does not mean it won’t melt away if you leave it sit in a puddle of water.

Here is the best hot process link with pictures I have seen:
I pretty much learned how to do it from that page!

If any of you have other questions on soapmaking, you can reach my email link on my website. Great pictures and blog–just wanted to make sure you end up with a safe product that won’t remove three layers of skin or blind you.

Daisy March 20, 2015 at 6:05 pm

Jackie–Thanks so much for all the great information! I will definitely follow your advice next time I try this. I usually do CP, but I’d love to have a good HP.

Patti Anderson June 13, 2016 at 5:15 pm

If you could give me the measurements that would be great . And also can you use other types of molds? And I didn’t see any of the ways to make it in the cold process . Would like to see them too. Thank you for your time

Daisy June 13, 2016 at 8:23 pm

Patti Anderson–This was a recipe from here: You can make it in any mold you prefer. If you want, you can also make it according to the cold process method.

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