Making Hot Process Soap in a Crock Pot

by Daisy on 09/25/2008

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I made famous soap today. Well, my soap isn’t famous, but the recipe is. Sort of. In a soapy kind of way.

It is a Hot Process Crock Pot, Oatmeal & Honey Castile soap recipe, known interchangeably as Kaleb’s Oatmeal & Honey Castile or Bunny’s Castile.

Soapers (people who make homemade soap) will understand what I just wrote, but for those normal folks out there who still haven’t nodded off, allow me to translate into English:

In (extreme) brief, there are two basic ways to make soap at home–cold process and hot process:

Cold Process: Combine oil(s) with a solution of water and sodium hydroxide (lye).

Hot Process: Combine oil(s) with a solution of water and sodium hydroxide (lye) and cook.

One method of hot process is the Crock Pot Method. Simply, you do the aforementioned cooking in a crock pot. A crock pot is desirable for this because it cooks slowly and evenly and is less likely to scorch.

Why one method over another? Many people do both, and some are strictly cp’ers only or hp’ers only. Cold process soaps tend to be smoother textured and take the fine details of a mold better than hot process. Hot process is favored by some because the cooking completes the saponification process and allows for a shorter cure time than cp soap. Some prefer the hp texture–rustic and handmade.

Finally, Castile soap is olive oil soap. That was easy. Well, not so fast. Castile also sometimes refers to soap made with vegetable oil only and no animal fat, especially if a high percentage of that oil is olive. Castile soap is mild, conditioning, and non-comedogenic. It takes a long time to cure (4-12 months), but once it is cured it makes a very hard, durable, and, in my opinion, superior bar.

Okay, back to the famous soap recipe. You can read all about it on the Latherings Forum, including the recipe itself and several soapers’ experiences with making it, including a few problems along the way. Suffice it to say that the word on soap street is that it’s great, and I had to try it. I am not quoting the recipe here because I think going to the forum with all its tips and caveats and anecdotal information is the best place to be when trying it out.

Here follows my first experience with this recipe:

These are the ingredients all spread out–olive oil, a little bit of castor oil, sodium hydroxide, water, oatmeal flour, & honey. That’s all it takes.

Gloves and Goggles! Don’t hurt yourself. Soap making is not rocket science, but it can be tricky and it has its safety issues. Here is one place to get up to speed on how to be safe. Here’s another.

I put the olive oil in the crock pot and added the castor oil to it.

The lye goes into the water, not the other way around or you may get a volcano/explosion. Visualize snow falling on a lake to remember. Stir to dissolve the lye completely.

Then the lye/water goes into the oils.

As I gave it a stir, the oil went from clear to opaque. The saponification process had begun.

I used an immersion blender to bring the mixture to trace. “Trace” is the point at which the mixture goes from liquid to pudding-y and a trace of the mixture will remain on the surface of the pudding for a bit when drizzled on the top. It took about 15 minutes. (Side note: If this were Cold Process, this would be the final step before adding the honey and oatmeal and pouring into the mold(s). But we are hot processing today, and so the story continues. . . )

I put on the cover and stirred occasionally.

After about 15-20 minutes it began to look like this:

I kept stirring periodically. It eventually went from foam on the edges to completely foamed-over:I stirred it back down and observed the separation phase. It looked like an oily, curdled soup. I let it
cook just a wee bit longer before turning off the heat and adding my honey and oatmeal.

In goes a slurry of 3 tablespoons of oat flour blended with a couple of tablespoons water (stir with fingers to make sure no lumps) and 3 tablespoons honey.

The mixture darkens a bit an thickens a little.

Now it was supposedly ready to mold. Never having HP’d before, I molded it up while it was still very liquidy. I am not sure how long I should have cooked it. Perhaps it was undercooked, perhaps it was overcooked. Perhaps the oil/lye ratio needed tweaking. Possibly the soap fairies were working a bit of mischief. All I know it was an oily, separated soup.

This wouldn’t do. I spooned it back out of the mold into the crock pot and did the only thing I could think of: I re-blended it with the immersion blender. And what do you know? The stuff set up immediately. A few short bursts with the blender and a bit of stirring to make sure it was homogenized and it went back in the mold.

Next day, it was solid enough to cut. I put it in my homemade Soap Guillotine:

It made 11 very thick, big bars. They will lighten up in color somewhat as they dry, but they are still probably darker than the perfect Bunny’s Castile, though I have never seen a photo of anyone else’s. If you have tried this and have a pic, I would love to see it and hear your comments on what I did wrong.

The soap was still oilier than I am used to in cold process. I would use this recipe again with caution. I think it is going to cure out very nicely, but it may take a while. Some people use their hot process soaps almost immediately, especially if they are not using olive oil, but I think this castile is going to need a good few months to reach its full potential. I can tell that it is already much milder than my cold process soaps at this point (day two)–the cold process soaps can be mildly caustic to the skin for weeks–this soap isn’t. For anyone trying out hot process (or cold process for that matter) for the first time, I would recommend starting with a recipe with no additives such as the honey and oatmeal in this case. They tend to complicate matters.
I must say, though, that this soap smells good enough to eat. It makes my mouth water every time I go near it.

This site has an excellent tutorial on how to line your soap molds. Basically, make a cardboard box the size of the inside of your mold and cover that with freezer paper. Voila, practically perfect mold liner.

This is also where I got the plan for the wooden log soap mold seen here. I like it a lot. It is the easiest thing in the world to unmold. Just take off the removable ends and lower the hinged sides.

Here are a couple of can’t miss hot process tutorials: Hot Process Soap Making by Gracefruit & Zensoaps Hot Process Double-Boiler method. And of course, my favorite spot for soapmaking in general is always Kathy Miller’s site.

One more thing. I picked up a crock pot at a thrift store for soap making only. If you get a second-hand one you want to plug it in at the store to make sure it’s in working order.

{ 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. ๐Ÿ™‚

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!) ๐Ÿ™‚

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. ๐Ÿ™‚ 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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