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!


{ 50 comments… read them below or add one }

Jo September 25, 2008 at 11:57 pm

Ohhhh that soap looks really nice. I want! I wish I had the patience to make soap… but admittedly I don’t 🙂

Tomato Lady September 26, 2008 at 1:46 am

If you can cook (and boy can you cook) you can make soap. I do hate waiting for it to cure, though, so I see your point.

Altered-gypsy September 26, 2008 at 3:28 pm

You have won the “I love your blog” award:


Elisabeth October 1, 2008 at 1:19 pm

What a great idea. Thanks for all the links too.

I’ve made several batches of soap in the past but it’s been quite a long while. I still have all the ingredients though and would like to do some more.


Tomato Lady October 1, 2008 at 1:48 pm

Thanks and you are welcome, Elisabeth. I have learned a lot from those sites. Soap making is kinda addictive, isn’t it?

KattyBlackyard June 15, 2009 at 3:29 am

Hi, interest post. I’ll write you later about few questions!

carla moffatt July 17, 2009 at 12:06 am

I was so freaked out to make HP soap, but your instructions were so great, it was easy! I had so much fun that I am about to make another batch right now! Thank you!

Tomato Lady July 17, 2009 at 12:19 am

Awesome, carla! I need to make a batch myself! Running low . . .

Al August 29, 2009 at 12:42 pm

Quick question…. can you make this crockpot soap out of the leftover bacon drippings that you used in another post? And if I can, do I still have to buy other fats?

Tomato Lady August 29, 2009 at 1:52 pm

Hi Al–You can make crockpot soap with bacon fat. Clean the drippings as described in the bacon soap post and use the crockpot method using the resulting fat as your oil. You can also combine the bacon/drippings fat with other oils if you like. Use a lye calculator like this one: and plug in your weights to get the amount of water and lye you will need. If you are just starting to make soap, I recommend using a recipe that doesn’t have add-ins such as oatmeal and which use milk. Add-ins is an issue you can battle after you have a couple unqualified successes under your belt.
I’m not sure I’ve answered your question, so please let me know if I’ve just been confusing. Good luck!

Al September 5, 2009 at 12:36 am

You answered my question. Thank you. Yes I’m a beginner and am wanting to make my first batch soon. At some point I would even like to make my own lye (scary!). Oh, and thanks for the link too… I’m finding it hard to find ratios and recepies. Most tutorials are for “those who are familiar with soap making”. I need all the help I can get! lol.

Al September 5, 2009 at 12:54 am

Ooops! Another question lol! I was just sitting and making a list of things I need for my first batch. Now, I was wondering, do the essential oils count as add ins? Should I make my first batch unscented just to keep it simple?

Angela October 11, 2009 at 10:44 pm

Made my first batch of HP soap today, not sure if it will turn out-that is how I ran into your website. The soap did look like your pics. I thought there was way too much oil separating from the soap so I kept turning the crock pot on and off 15-20 min at a time for about an hour. The final result resembled vaseline when I poured it. I also noted some liquid at the bottom of the crock while I was pouring it. Guess I’ll find out in the morning if it will turn out.

Angela from Missouri

Tomato Lady October 13, 2009 at 7:20 am

Angela–Hope it ends up ok. I think I’m going to stick with cp for the most part. Although hp has some nice advantages. . .

Cindy October 21, 2009 at 5:31 am

Thank you for the excellent tutorial and the links for the molds and guillotine!!! My sweety took the picture out to the shop and came back with a mold and a guillotine, so I was prepared. I am hooked on crockpot soaping!! I made my first batch on Monday. It just all came together so easy! It cooked for 1/2 hour — I was expecting more. Glopped it out (very nice mashed potatoes), unmolded the next morning and sliced. 17 bars of wonderful soap!!

However, I made another batch last night. This time I used goat’s milk for the water. Hmmm, after 4 hours of cooking, I had to go to bed (12:15 a.m. at this point)!!!!! It’s still tingy to the tongue. I have to go out of town for today, so I’m hoping I can chunk up and rebatch when I get home. I’ll try it, it can’t hurt!

Jenny August 24, 2011 at 2:12 pm

I have done this recipe when you first posted this and loved the ease and quickness of it. My question is how to get more lather. I read somewhere to put sugar in. Would you put it in with the oils or with the oat flour? I love your blog. I have gained a lot of info from you, thank you so much for all you do.

Tomato Lady August 25, 2011 at 6:01 am

Jenny–Thank you!
Here’s an answer with different methods. Hope it helps:

Deb September 11, 2011 at 7:33 am

Hi. I have a few questions and a comment. I’ll start with the comment. Adding castor oil to your mix will make nice suds.

Now the questions: Can you use any recipe for hot process that you do for cold process? And does anyone have a basic recipe for a milk soap using lard only? All I have to get online with is my phone and it won’t run the soap calculator right. Thank you.

Tomato Lady September 11, 2011 at 3:32 pm

Deb–I believe, in theory, cp and hp recipes are similar proportions. You may choose, especially in the beginning, to use some “tried and true” hp recipes while you are becoming comfortable with it, i.e., recipes that go along with particular tutorials, especially as they are often designed around certain batch sizes for, say, X-capacity crock pots or certain size pans for oven or direct heat or double boilers.

I found this recipe:, authored by “Wendy,” (props to Wendy : ) ) and ran it through the mms lye calculator. In the “green” range (5%-8% excess fat range–the recommended range) the lye suggested is from 9.12 to 8.83 oz., so the recipe’s 8.5 oz. lye is nicely within that range. The liquid suggested for those oils (1 # coconut and 3 # lard) is 16-24 oz. also within the recipe’s 24 oz. goat milk. So, sounds like a winner. If you want to use all lard for that same size batch, i.e. 64 oz. lard, the lye calculator for the green range suggests from 8.43-8.17 oz. lye and again, 16-24 oz. liquid.

Hope this helps, Deb.

Deb September 11, 2011 at 3:59 pm

Thank you so much. I forgot to mention that my crock pot comfortably makes a batch of soap using 32oz. of fat, and my mold is a 2 lb. mold. I use a basic soap recipe that calls for 30oz. lard, 2oz. castor oil, 10oz. water, and 4.5oz. lye. It makes great soap, and takes fragrances well. I don’t use dyes. Do I just divide the recipe that you gave me, or will it need to be recalculated? Thank you.

Tomato Lady September 11, 2011 at 7:59 pm

Deb–Do you want to do 100% lard or part coconut oil? If you tell me the recipe you’ve decided on I’ll run it through the calculator for you.

Deb September 12, 2011 at 6:51 am

Good morning! Thank you for taking the time to do this. I want to do the 30 oz. lard and 2 oz. castor oil recipe. Coconut oil is too pricey for me right now.

I have customers requesting milk soap, so the other day, I tried to make milk and honey soap, but I think I scorched the milk. (I didn’t freeze it.) But I did sit it the container I mixed the lye into it with down in a bowl of ice. It turned brown and curdled. I added it to my oils anyway, and it smelled just awful. Then, at trace, I added the honey. it started turning a really neat orange color, then it just got darker and darker, and smelled so AWFUL! I had to pitch it. YUCK

Deb September 12, 2011 at 7:03 am

Me again. Did I add the honey at the right time?

Also, for any basic soap recipe, can you use milk for the liquid, and still use the same amount of lye and oils? I am very amateur at this.

I’m also wondering if you can use coffee for the liquid without needing to adjust the lye.

Finally, does anybody know of a book that I can get that is about soapmaking for absolute dummies? Thanks!

Tomato Lady September 12, 2011 at 7:42 am

Deb–The lye calc says: 8-12 oz. liquid, 4.20-4.07 oz. lye (within the green range).
As for the milk, everything I’ve ever read says freezing the milk is key. The honey does need to be added at trace. Sounds like things were headed downhill already and the honey was just the final straw at that point. I would make sure the lye/water mixture has cooled sufficiently (patience patience–so hard when you’re in soap mode! : ) then definitely use frozen milk, omitting the honey at least until the milk-only version wants to behave, then once that issue is squared away, trying a little honey in a small batch.

Deb September 12, 2011 at 10:10 am

Working on it right now! This is SO addictive. I already had my milk in the freezer. I also turned down my crock pot a hair. I think it’s gonna work this time. My 9 mo. old decides to get fussy at this time. Geesh! By the way, your site is awesome.

Tomato Lady September 12, 2011 at 10:18 am

Deb–Thank you! Let me know how it turns out!

Deb September 12, 2011 at 10:56 am

Well, it’s in the mold! I have a confession. I snuck about an ounce of honey in it at thick trace a little bit at a time. I wasn’t brave enough to add more. Anyway, when it was done, I blopped it into the mold. I tested a cooled blob as usual, and oh, what lather! It smells nutty, and such a nice color! Can’t wait to make some more and add some yummy scents. Thanks! Gotta make new labels now.

Deb September 12, 2011 at 3:48 pm

And now my bars are cut. Smells just like Bit-O-Honey candy.

Tomato Lady September 12, 2011 at 7:01 pm

Deb–Sounds delicious!

Kim B. September 16, 2011 at 2:18 pm

when doing HP soap in the crockpot you have to let it bubble up like it did and fold into itself 2 times. After the 1st time scrap it down and stir it then let it bubble up and fold into itself one more time. Stir it…it should be the consistency of weird looking vasaline then add FO, EO..any other additives. Stir and then it is ready for the mold.

Melissa October 13, 2011 at 5:59 pm

Thank you so much for the pictures and tutorial. I referred to it many times as I made my own crock pot soap. This is my first time to try hp soap. Can’t wait to see how it turns out.

Beth Shaffer November 13, 2011 at 9:08 pm

I have been making CP soap for a couple of years. I tried HP today and oh boy did I have a huge mess! My brother & I could not stop laughing at the way it was growing out of the crockpot!!! We still had enough, ok more then enough to make an 8# loaf of soap! It smells so wonderful and I am so excited that I don’t have to wait 3 to 4 weeks for it to cure! Thanks for the great info! We have all of our CP on our website and soon we will have the HP!

joss November 13, 2011 at 11:33 pm

Was there a post on this blog about using a slow cooker to rebatch soap? Not necessarily in such a way as to fix a problem (like too much lye or whatnot), but just to be able to add delicate ingredients (flower petals, essential oils) that would be mostly fried by the initial chemical reaction? I thought there was but now I can’t find it. Thank you!

Tomato Lady November 14, 2011 at 8:29 am

joss–There’s this:, and perhaps this:

I’m not sure if either is what you remembered, but I think that’s as close as we come. Try also for rebatching tips.

joss November 14, 2011 at 10:05 pm

That’s it! Thank you!

Deanne Likkel Guthrie December 9, 2011 at 10:02 am

Where would I find the actual recipe for the Oatmeal & Honey Castile soap that you used in the crockpot tutorial? For some reason I can’t find it listed here, but I want to make sure that I have the right amounts before jumping in. Thank you for your detailed instructions!

Tomato Lady December 9, 2011 at 10:10 am

Deanne–Here’s the recipe I refer to in this post:
Thank you!

Jenn December 9, 2011 at 1:24 pm

I think I know what went wrong with the setting to begin with, I have watched a lot of different HP soap videos and in many of them they let it bubble over 2 or 3 times until it’s thick like mashed potatoes. Other than that I love you steps best of all I’ve seen. Could you share a recipe? Thanks, Jenn

Tomato Lady December 9, 2011 at 3:48 pm

Jenn–Good advice, thanks. The recipe I used was here:
We have other soap recipes under our “crafts” then “lye soaping” categories under our header.

Lee February 6, 2012 at 5:25 pm

I just ordered the lye for this project. Next is to get the castor oil. I’ll have to make a box of some kind. Also, I have a soap stamp I got made in Canada. You press it into the soap. At what point could I do this? Will the soap be soft enough to do that after cutting it into slices? Thanks. Sure looking forward to this.

Tomato Lady February 6, 2012 at 6:20 pm

Lee–Yes, you’ve got the idea. It should be soft enough at that point. Happy soaping!

Debbie April 18, 2012 at 11:11 pm

If your HP wasn’t a thick glop, it hadn’t cooked long enough. It takes quite awhile and just be thick like cottage cheese. Actually a bit thicker. It won’t pour and has to be spooned into the mold and then pressed down firmly or you’ll have air pockets. I would like to know what your recipe is for CP, that you think this is milder than your CP is. What I find with HP is that you are really cooking out most of the benefits. HP should really cure for the same amount of time as CP, even though there are those saying it doesn’t. Aged soap is a better product. I saw a seller that claimed that because they use the HP method there soap is fresh. Made me laugh! A long lasting mild bar comes with age, there is just no way around it. I grew up making soap on our family farm, many moons ago and have been making soap for over 20 years (not including the time growing up). 🙂

Debbie April 18, 2012 at 11:18 pm

Oh, I forgot! When using milk, use a frozen slush of milk and the key is to very slowing add your lye, only a little at a time. Constantly watching your temp, if it gets to hot you scorch the milk. Then instead of a golden beautiful color from goat milk, you will get a brown.

Jennifer P May 11, 2012 at 8:15 pm

Do you know how to make the soap smell like leather?

Daisy May 11, 2012 at 8:44 pm

Jennifer P–You can probably find a fragrance oil that smells like leather. I don’t know what you’d have to blend in terms of essential oils to get a leather smell. Good luck!

Beth May 22, 2012 at 3:13 pm

When do you turn on the crock pot?
I have been blending the oils and lye for twenty minutes and can’t get it to trace, so finally I turned on the crock pot to cook…I’m thinking maybe you cook while you are blending yours?
I had a really hard time with cp getting it to trace as well…though the lye calculator and I agree on the recipe.
I really enjoy your blog!

Daisy May 22, 2012 at 4:38 pm

Beth–This is the link for the original recipe:
It has you turn on the crock pot to preheat when you add the oils, and up to high after you reach trace.
Glad you enjoy the blog! Thank you!

Sue June 13, 2012 at 12:33 pm

Hi, I have made many batches of soap with no issues. Right now I am trying a new recipe that is a bit different and used soy oil. The soap has traced but will not go into that next step, in fact the oil is separating a bit. I know that the lye is still very strong. It’s been on low in the crock pot for 4 hours. Is there any way to save this?
I never made CP soap before…can I put this in a mold and let it cure for 4 weeks?
Really don’t want to waste the batch. Thanks!

Daisy June 13, 2012 at 2:42 pm

Sue–I wish I had the answer for you! I guess you can just mold it and hope for the best. I think I may have cooked mine to death, so I’m not sure I’m the best one to ask!

Katrianna@pretty chaotic July 24, 2012 at 9:51 am

Hi I was wondering how big is the crockpot you use in this tutorial? I’m wondering if a 1.5quart size crockpot is big enough to make batches.

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