All Time Best #5: Making Hot Process Soap in a Crock Pot

by Ivory Soap on 12/01/2014

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In honor of our 1000th post in October 2014, we are counting down our most popular posts of all time. Each has received over 100K hits, and some as high as 500K! This week, at #5, is Making Hot Process Soap in a Crock Pot!


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 might want to do this to make sure it is in working order.

Tags: castile soap, hot process soap, , soap molds, soap cutters


{ 16 comments… read them below or add one }

Cinnamon Vogue December 2, 2014 at 5:59 am

Oh this is brilliant information. Just what we were looking for. We are thinking of making an exotic all natural organic Ceylon Cinnamon Soap. Apparently cinnamon oil is good for the hair, so we figured we could do a hair only soap. Still researching on soap consumer regulations if any and trying to find a World class small manufacturer, so thank you for this post. The information and photos are fantastic.

Sallie December 2, 2014 at 8:53 am

Thanks for the tip about the crock pot…..I was worried.

Interesting process. It gives me courage to try on my own….once I find a used crock pot at a thrift store!!

Rhoda Edwards December 2, 2014 at 6:42 pm

Cool! I always wanted to make soap but for some reason I keep putting it off. You made this seem so easy that I think I want to try this recipe. Thank you.

sarah December 27, 2014 at 9:29 pm

For those looking for lye, look for roebic crystal drain opener. It is confirmed 100% lye and often used by soap makers.
It is sold at a great deal of small town hardware stores and larger chains as well. I’m not certain of the price but the last time I checked I remembered it was cheap

Trishalana Helsley Morrison December 28, 2014 at 9:03 am

Might I suggest crock pot liners?

Jerry Y. December 29, 2014 at 2:54 am

most crock pots have a hi and low setting, which did you use or does it matter?

Daisy December 29, 2014 at 11:22 am

Jerry Y.–While pots vary, low is generally recommended.

b December 30, 2014 at 7:41 pm

great article, but left me asking myself what setting for the crockpot? and how long the whole process took? measurements for the oils and additives?

Daisy December 30, 2014 at 8:31 pm

b–I use the crockpot on low, and here’s the link to the recipe: http://www.latheringsforum.com/bb/viewtopic.php?t=5612&highlight=bunnys+castile. Lots of comments about the process on the Latherings forum, links are in the post.

Perla January 4, 2015 at 7:41 pm

where is the actual recipe? I see the ingridients but no amounts. ????

Sarah January 5, 2015 at 12:15 am

Can crock pot liners be used in this process to preserve the crock pot??

Daisy January 5, 2015 at 1:42 am

Perla–The link to the recipe is in the post itself, Bunny’s Castile. This is more of a photo exploration than a recipe since it isn’t my unique creation but another person’s, just my experience of making it.

Daisy January 5, 2015 at 8:57 am

Sarah–I’ve never done it myself, but I don’t see why not. If you’re concerned the liner would leak, you could use the unlined pot for soap and the liner when you cook in it. Personally, I have a thrift store crock pot for soaping, melting paraffin for mushroom log inoculation, and dyeing. It was cheap and I don’t worry about it getting trashed. Many people use the same pot for soaping and cooking, and while that’s controversial, if you clean every nook and cranny, I don’t see the problem.

Teresa D Campbell August 2, 2015 at 3:54 pm

I love goat milk soap. Can you use that in this hot recipe or will it not work?

Catrina August 3, 2015 at 10:26 am

I had a question. I made soap a little while ago in the crock pot. I measured everything out then after it was done and supposed to be hardening for a cpl days it was still really soft. I realized I messed up on the lye. I did grams instead of oz. Can I do the conversion difference and put it back in the crock pot?

Daisy August 3, 2015 at 11:13 am

Catrina–If the soap is basically unusable at this point, I suppose it wouldn’t hurt, provided you can get it to melt back up. I’ve never tried it myself, so I can’t speak from experience. Good luck!

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