Want to Build Your Own Successful soap Biz?

A Hot Process Soap Tutorial: How to Hot Process Soap in a Crockpot

When I first started making hot process soap, I searched high and low for a definitive set of steps, like a recipe, that would ensure my hot process soap came out perfectly every time. However, once I understood saponification (the chemical reaction that happens when making soap) and was able to identify the stages of saponification, I became a lot more relaxed about hot process soapmaking.

The main concept of hot process soap is that you are actively cooking the soap (instead of letting it saponify on its own which you do with cold process). Today, we’re going to take a tour of hot process soapmaking using a crockpot, focusing on the stages of saponification. I intentionally named this post “a hot process tutorial” instead of “the hot process tutorial” because using a crockpot to make hot process soap is one of many ways to cook soap.

How to Make Hot Process Soap in a Crock Pot
How to Make Hot Process Soap in a Crock Pot

Making hot process soap is a lot like cooking a chicken. You can cook the chicken really fast over high heat, or you could cook it low and slow like BBQ.  Both methods will yield a cooked chicken, and both can result in a tasty meal. However, as a cook, you will likely develop a preference for how you like to cook chicken and probably stick with one method after you have tried a few. Cooking hot process soap is a lot like that!

You can cook soap in a crockpot like we are going to do here, or in a pot on the stove, or in the oven, or even without any additional heat sources. And they will all result in great soap if you are able to identify when the soap is done, and if you manage the heat and water levels properly. In other words, there is no best method for hot process: what matters is that you choose a method you like and you learn how to identify the stages.

My Only Rule for Hot Process Soapmaking

I only have one rule when it comes to hot process soapmaking: never leave your hot process soap while it is cooking. (I have broken this rule a few times and greatly regretted it!) Don’t go in the other room to change the laundry or go outside to get the mail. Unattended hot process soap can grow in size (creating a soap volcano), making a huge mess and resulting in a failed batch of soap. If you follow this one rule, you will always be there when your soap starts to volcano, and you can save it, but if you are in the other room on the phone, it can be a messy disaster!

Making Hot Process Soap in a Crockpot

Let’s get started on making soap in a crockpot! I like to make my hot process soap in the crockpot on the “low” setting.  When you cook hot process soap at a lower heat, there is a lower risk of a volcano.

Like cold process soapmaking, I make my lye solution and allow it to cool for a while (about 15 to 20 minutes).  Again, I do this to keep my temperatures low and minimize any chances for soapy volcano.

For this batch of hot process soap, I heated my oils to 150° F (65° C) and added my lye solution after the solution cooled for a good half hour.  I like to make my lye solution in a stainless steel pitcher (you can see it in the photo below).

Getting ready to hot process soap in a crockpot: melting & heating the oils
Getting ready to hot process soap in a crockpot: melting & heating the oils

If you don’t want to wait or your lye solution to cool or you want to heat your oils to a higher temperature, don’t worry! As long as you don’t leave your soap unattended, you will be able to stir the soap volcano down with a large whisk.

You do not want your oils hotter than 180° F (82° C). Warning: If you add hot lye solution to really hot oils in a heated crockpot you will have a huge, super hot mess on your hands.  If you are making hot process soap in a crockpot for the first time, I definitely recommend keep your oils and lye solution on the cooler side (below 150° F/65° C).

To check your temperatures without ending up with a messy thermometer coated with caustic material, get yourself an infrared thermometer. An infrared thermometer is probably the only soaping gadget I cannot live without! You have to know your temperatures when you hot process, not just to avoid soapy volcanoes but also to check when the soap is cooked and you want to add your post-cook goodies.

After adding my cooled lye solution to the warmed oils in the crock pot, I stick blend to emulsion. (Not sure what emulsion is? This post about controlling trace in cold process soapmaking will help!)  You definitely want the mixture to thicken, but once it is blended, you are done with your stick blender!

After mixing your oils and lye solution together, cover the crock pot to retain moisture and avoid dry spots.  I like to cover mine crock pot with plastic wrap (much thanks to Sharon Johnson for teaching me this super cool trick!).

Getting ready to hot process soap in a crockpot: combining the lye solution and oils, starting the cook!
Getting ready to hot process soap in a crockpot: combining the lye solution and oils, starting the cook!

I always use Stretch-Tite plastic wrap, because it is thicker, holds up to heat, and does not cling to itself.  I have tried many brands, and none compare to this one. You can get it at many grocery stores (Publix carries it) as well as Costco. Costco sells huge rolls if you have room to store one that big!

Stretch-Tite plastic food wrap is my favorite brand of plastic wrap to use when hot processing soap in a crockpot.
Stretch-Tite plastic food wrap is my favorite brand of plastic wrap to use when hot processing soap in a crockpot.

The purpose of the plastic wrap is to seal the crockpot to prevent moisture from escaping.  If you want to have a fluid soap that you can swirl when hot processing, retaining water is important vital.  Some soapmakers use a damp towel and place it under the lid, which helps retain water. However, you need to open the lid to check on your hot process soap during the cook, and doing so with a damp towel will allow the water/steam to escape.  That is why the plastic wrap is great: you can watch the soap cook, and even check the temperature with an infrared thermometer without letting any water escape!

For these photos, I opened the plastic wrap to get clearer shots, but normally I would leave it alone until it is done cooking!  Some soapers like to stir their hot process soap as it cooks, but I don’t because of the evaporation issue. This batch of hot process soap was remarkably less fluid than my normal batches due to taking the plastic wrap off, confirming that one should keep that lid on tight!!

Making hot process soap in a crock pot: The edges gelling!
Making hot process soap in a crock pot: The edges gelling!

Now, the fun part: waiting! 

After your blend your oils and lye solution to an emulsion, the raw soap mixture will be opaque (meaning you cannot see through it). It is usually a cream color (like butter!), but the color can vary depending on the oils used.

As the soap cooks in the crock pot, it will start to gel along the sides of the crock pot, because that is where the soap is hottest.  You can tell the soap is gelling because it becomes translucent (which means you can kind of see through it and it looks like jelly).  Once the soap is fully gelled, it is done cooking!

Using the chicken example before: you know you want to cook chicken to an internal temp of 170° F (76° C) so you can remove it from the heat slightly before and the residual heat will continue cooking the chicken. With hot process soap, you can also remove the soap from the heat before it is fully cooked, knowing that the residual heat from the crockpot will finish cooking the soap!

Once the majority of the soap is gelled, I take the crockpot out of the base, remove the plastic wrap and give it a stir. After mixing the hot process soap, I will check the temperature with my infrared thermometer.  In most cases, the soap will temp between 200° F (93° C) and 220° F (104° C).

If you wanted to put the soap in the mold at this point, you can. Even if the soap is not fully gelled, it will finish saponifying in the mold which is why I don’t stress about confirming if the soap is fully cooked via a zap test or pheno. It does not matter: it will finish itself off in the mold!

Making hot process soap in a crock pot: gelled soap!
Making hot process soap in a crock pot: gelled soap!

Wait, what is a zap test?  A zap test is an old-fashioned way to check a soap mixture for the presence of lye by touching it to your tongue. If it feels zappy or sharp, like touching a battery to your tongue, it’s not done yet. While I have done a zap test, I don’t recommend it at all!  Not only does soap taste bad, but it is dangerous and can give you a chemical burn or thermal burn if the soap has too much lye present or is too hot. (The zap test is also a safety, liability, and GMP nightmare for soap business owners, with or without employees.) I much prefer to go by temperature and look rather than risking my tongue!

If you want to add any fragrance or additives like honey or goat milk, you will want to let the soap cool down before adding them.  Adding honey or goat milk to really hot soap can cause the sugars to scorch, and the soap will turn brown.  If you add a fragrance to soap that it is too hot, it can vaporize and your soap won’t have as much scent. Your soap room will be heavily scented though! Ask me why my husband made me promise to never make patchouli soap again early on in my hot process days. 😉

Okay, I know what you are thinking: flashpoints. I’m sure you have heard or seen it before: I have to add my fragrance when the soap temp is lower than the flashpoint.  Let’s clear this up!

I went through a phase last year where I was determined to understand the relationship between soap temperature and flashpoints. I will jump to the end of this exciting story: flashpoints are solely for the safe storage and shipping of fragrances.  (Kenna also mentioned this in a previous article about common questions about using essential oils in soapmaking!) A flashpoint refers to the temperature at which the fragrance will combust from an open flame.  In my experiences making hundreds of batches of making hot process soaps, there is no relationship between the specific flashpoint of a fragrance and when to add to soap.

However, fragrance oil and essential oil will both vaporize a bit (or a lot) if you add them when the soap is too hot (200° F or 93° C and higher) so if you want your scent to stick, let the soap cool to less than 180° F (82° C).  This can take some time, so cover your soap back up with plastic wrap and wait. (And yes, it is okay at this point to leave your soap unattended for a bit if you need to!)

Hot process soap with all my goodies added in!
Hot process soap with all my goodies added in!

Once the soap cools, add your superfat, goat’s milk or whatever other post cook goodies you want to add. We will talk more about swirling and additives in future articles, but this is also the point where you would divide your hot process soap for coloring.

If I want a fluid hot process soap, I will add yogurt after the cook (at the rate of 1 tablespoon per pound of oil). I have used greek yogurt and regular full-fat yogurt, and prefer the regular yogurt because it is more fluid and easier to blend in.  You should discount your total amount of water for your lye solution to account for the yogurt, just like you would in cold process soapmaking. For example, if your recipe calls for 10 oz of water and you want to add 1 ounce of yogurt, you will only use 9 ounces of water for your lye solution. Be careful here though: you must have as much water as you do lye for the lye to fully dissolve in your solution! After adding the yogurt, I cover the crock pot again with plastic wrap and let it rest for a minute. You will be amazed at how much more fluid it is after the yogurt does its thing!

Here’s my top tips if you are getting ready to make your first batch of hot process soap:

  1. Keep it simple.  Use only one color, or no color, so you can focus on the process itself.  Add your superfat after the cook, but avoid honey and milk for now.
  2. Use a loaf mold or a slab mold for your first batch! Using a loaf or slab mold rather than individual cavity molds will give you more room to mold the hot process soap.
  3. Use a recipe that you have tried in cold process soap before and liked. You may even want to compare the soap recipe made the two different ways!
  4. Keep your eyes on your soap! Watching the soap gel along the outside of the crockpot will really help you with hot process soapmaking by being able to identify the stages.
  5. Don’t stress about whether the soap is completely cooked before taking out of the crock!  It will finish cooking in the mold and overcooked soap is a lot like overcooked chicken. No bueno!
  6. Don’t leave the soap alone until it is done cooking and you are waiting for it to cool down.

I hope this helps you rock your first hot process soap in a crock pot! Next time, we will dive into swirling hot process soap!  Feel free to leave a comment below with any questions you have regarding hot process soapmaking so that I can cover it in the future!

Share this post

Share on pinterest
Share on facebook
Share on reddit
Share on twitter
Share on linkedin
Share on print
Share on email

Remember to keep it clean (oh, so punny). We moderate comments for keyboard warriors and spam, read our comment policy for more information. If you need a little extra TLC, please reach out so we can best serve you!

141 Responses

    1. Thank you for answering the many questions that I couldn’t find answers for anywhere else! Your commonsense approach was very much appreciated! Thanks!

    2. Such great information. I had to rebatch soap today and found your information. Only thing i would add 8s this can be done in a crock pot bag liner so cleanup is a breeze.

  1. Thanks, Molly. I’ve been prepping to move into hot process, and this puts some concerns to rest. I can’t wait for your next article!

  2. Molly, if you don’t stir the soap while it is cooking will it stick to the bottom of your crock pot and burn? Are chunks of soap an issue if you don’t stir? Also just to make sure I understand (sorry new to soaping) Do I stop cooking the soap when the gel starts around the edges or when the whole batch has a gel look. Thanks for the great post and help

    1. Hi Ruby,

      I actually find stirring to be a bigger cause of white soap chunks in soap – as you stir, it gets soap on the sides of the pot higher than the level of the soap and those bits dry out. when i dont stir during the cook, that happens to me less. I tend to stop cooking the soap when it is about 2/3rd done gelling. the rest of the soap will gel while I wait for it to cool down so that I can add my post cook additives.

  3. What size crock pot are you using? I have been doing cold process for 11 years and Sometimes I cold process/oven process but crock pot hot process interests me. I usually make 4.5 lb oil batches. How full would you let the crock pot be at the start? How much does it creep up the sides? Your tutorial is great and I am excited to try this process! Really looking forward to your next tutorial about swirling!!

    1. I use a 6 quart crock, and I would never want it to be more than half full. Less than that is ideal in case it volcanos. this is one of the reasons i stopped using the crockpot – mine was not big enough for bigger batches. I will talk about how I make soap now in a future post as it a more advanced technique and believe that it is better and safe to get introduced to HP via a slow cooker.

  4. Hi – I make a lot of HP in a crockpot. I have found I need to stir during cooking or I risk it boiling right up and out of my crockpot. Have you had that happen? Is there a secret to avoiding this every time?

    If you cover with plastic wrap what happens if the soap bubbles up and touches the plastic? Does it melt into the soap?

    Thank you. Enjoyed reading this tutorial.

    1. Hi Terry,

      When soap volcanoes in the crock, it usually means the soap is too hot, or that you have filled the crock too much. If you add your cooled lye water when your oils are around 150, you should not have much volcano-ing. However, i have added my lye when it was too hot to oils that were too hot many times, and that is why you need to be watching it. when that happens, take off the plastic wrap and stir it quickly with a whisk. you will lose some water which is why i recommend avoiding this, but it will prevent the soap from expanding out of your crockpot. happy soaping!

    1. It varies based on how hot your oils were, how hot your crock it, and how much soap you have in there. That is why I tend to avoid times for this type of soaping. It should take between 30 and 60 minutes though. It will go faster if the various elements are hotter, but be careful. Hotter = greater likelihood of a volcano which can make a mess in a crock if unattended.

  5. I found your tutorial very helpful for the hot process crock pot method. I’m definitely going to get an infrared thermometer. I don’t have a crock pot so I’ve been doing the oven process method. I’ve never heard about covering the soap to keep the liquid in before. This sounds great because it always seems to get too dry to add anything to it. What do you recommend to use to cover the soap in the oven? I could use foil and just cook it for 45-60 minutes and then stir and check. I’ve never had oven process soap boil up like crock pot soap apparently does. I will also definitely try the yogurt trick. Any oven process hints would be appreciated! Thanks!!

    1. I have never done oven HP, but lots of soapers do. I sometimes cook my soap on the stove top though so i guess the idea is similar. I see no reason why you could not use a thick saran wrap that is safe for the oven temps you use. I often eat additives in the oven at 170 with stretch tite on them and have never had an issue with the saran melting. but at high temps it could so be careful!

  6. I totally just did this for the first time after reading your series here and on your blog. It is SO HARD to resist the urge to stir! But I did, and it turned out awesome! I used a recipe that I actually have trouble doing CP with. It always seizes on me since it has beeswax and cocoa butter in it, and I always seem to soap at too low a temp for that recipe. It’s a customer favorite though, so I gave this HP method a try. The batter was way more fluid than it is with CP and was way easier to work with. For that particular soap, I am a convert! Thank you so much for sharing all this information! It came at just the right time for me 🙂

    1. That is great to hear Angela! I was reminded again this week why I love HP. I made a batch of CP soaps in detailed molds using a floral FO and the batter riced up instantly after adding the FO. that never happens with HP!

      1. I made hot processed soap years ago and hated it. I’ve been soap making for about five years. Not until this week did I revisit the thought, and found your page. Good Lord you took the sting out of it. The constant stirring I did years ago did not make my soap turn out like it did when I used your method. I’m in love with hot processed soap now thanks to you. It has such a rustic look, and my milk did not sour. The honey looks beautiful in it. Letting that temperature drop was the key, but no one explains it like you. I used pH strips, and my numbers were as good as it can get. Thank you so much for the wonderful and simple instructions.

        1. you could do that – many soapers do it that way. I superfat my soaps at 8% but just add the 5% after the cook so i just put that amount aside. There is no fantastic reason to do it that way, i just started doing it that way early on and it works for me.

  7. Great series on Hot process. Look forward to the next entry. I have made a few batches using double boil stove top. Soaps seem to have come out well but just did not have the shelf life of my cold process soap. After time (3-4 months) they were waxy in feel and smell. To this day probably the only soap I have ever tossed. I would love to make another go at it 🙂

  8. Great Tutorial – Something I have been searching for quite some time!
    I have been hot processing for about a year and a half now. I never cold processed because I wanted to make/duplicate Martin de Candre shaving soap which, I believe is only made via hot process (HP). Besides, I’m way too impatient to wait 4-6-8 weeks to use the soap if made cold process. Then I figured, what-the-heck, let’s make some hand/body soap which I also did HP. All batches went very well. Although, I did go to my kitchen table one time to measure my essential oils (EO) and, I was not there for the volcano. Fortunately, by the time I went back, it only flowed over the rim of the pot and a little dripped down the side to the counter. I used my spatula to mix it down and the batch was saved and, a lesson learned. From my first batch and beyond, I did/do a lot of reading online but, nothing comes close to your tutorial, most of which I was able to figure out along the way by trial and error. I have never used the zap test and, like you, had gone by appearance, which worked quite fine until I read about Phenolphthalein 1% and now use that to determine when the cook is done. I just have a few questions.
    1. Flash Point – I’ve been wrestling with this for a while and can’t find anything definitive online. I have been using only EOs to go with a truly 100% natural soap. You mention to wait until the temp is below 180 degrees to add fragrance oils. What if the flashpoint is 160 or even 140 (or lower) as is the case with some citrus EOs, can I still add it at 180 or should I wait until the batch gets below a particular oil’s flashpoint? As you know, waiting until it gets below 150 makes the batch that much harder to work with.
    2. I once added 25% coconut milk to the lye/water solution and it all worked out fine. I once added beer and it did turn brown and smelled a bit like caramelized sugar. If I do add beer again or goat milk, should I do it at the end of the cook? And, I’m guessing if I do, I should subtract the amount used from the water in the lye solution?
    3. To help with the problem of fluidity at the end of the cook, I have been adding 3-5% extra water than that called for in Soap Calc. I have been having decent results but, it varies. What do you think? But, I will definitely be trying your tip about adding yogurt.
    4. Can adding a little more water also solve the problem of evaporation and just use the crock pot cover instead of plastic wrap?
    Thanks again and Luv Your Site!

    1. 1- I also have had a hard time determining if flash points apply to HP soaping, however, since I made a concerted effort to only add my EO or FO after the soap had cooled, i have had a lot more success getting the scent to stick.
      2- I always add my non-water liquids after the cook. I did not used to do that but got tired of funky colored and funky smelling soap. yes, discount that from the total amount of water needed for the recipe
      3- you can add water (make sure it is hot). I add goat milk but the idea is the same in terms of the needed liquid. i don’t formally account for the yogurt i add other than soaping at a somewhat lower water percent (i soap at 35%)
      4. it could in theory but how would you know much water evaporates? i dont have scale that could hold my crockpot so that does not seem like a reliable method for me. I am all about consistency as I want every soap to turn out the same in terms of hardness, etc.
      Thanks for your kind words and let me know if you have more questions!

      1. Hi Molly,

        1- You suggest not to add honey in HP for now. I use a lot honey in my CP soaps and the creamy final color is just a pleasure for my customers.
        When can It be added in HP ( ie. the best temperature)? how much of the total oils to avoid the brown color? Also do I need to reduce the amount of water if I decide to add honey at the end of the process?
        2- I am still confused with the yogourt part. Does the amount of fat in the yogourt have an impact in my soap formulation? Do I need to use a specific type of yogourt?
        3- I use multiple cavity told for my soaps. Is the final texture fluid enough to pour it in ? because when I see the picture It seems that the final texture is not fluid enough.

        I am not sure about HP but I really want to give it a try (too tired of waiting 4 weeks for my soaps). Your tutorial gives me some hope.

        Thanks a lot


        1. Hi Mona,
          1 – I dont use honey often, but when I do, I mix it with a little hot water and add when the temps are below 180
          2 – The yogurt will be providing additional superfat but i dont really worry about it. my fave yogurt right now is dannon full fat plain, regular yogurt. I used greek yogurt for ages and i think the regular yogurt is easier to blend in. but you can use any kind of plain yogurt that you like. if you are worried about the SF, use non-fat
          3 – i have dabbled in this a bit and the soaps came out good, not fantastic. you want to soap with a higher water level (try 38%) and once you get that fluid batter, get them in the molds. I suggest heating the molds in a warm oven and i like to spray with alcohol to break the surface tension in an attempt to prevent bubbles. nice thing about this method is you won’t get ash which I am not a fan of.

          1. For hot process adding yogurt or real fruit at the end of sponifcation. ( along with super fats). I was concerned about trying thinking fresh fruit or yogurt may mold.. How is this done properly?. Will it mold or rot?

  9. Thank you Molly, very well explained your HP method, I’ll give it a try. I just have a question though, about the yogurt, does it have to be used at room temperature? And I have heard about adding syrup at the end of the process to keep the soap fluid, any thoughts?

  10. Hi Molly!
    Can you explain what you mean in your comment #3 to Alan above, where you say you soap at 35%? What does that mean in terms of the amount of lye & water? Can you give an example?
    Thank you so much for you help and your wonderful tutorial.

  11. I have been making hot process for a while, since my best selling fragrance totally seizes in cold process, and I’m also very impatient waiting on cold process. I had read before that I didn’t have to worry about the temperatures when mixing. I have the same crockpot and usually put in my liquid oils while microwaving my palm, then combine them and let them heat up while I mix my lye, then add it and mix it in the oils. I tried your plastic wrap idea, I also like Stretch-Tite, but it started ballooning on me, looking like it was going to explode! I lifted a small corner to let out some steam, but I still didn’t like the plastic idea, between the ballooning and it looking like the sides were melting to the crockpot.
    I also love adding yogurt, between that and my superfat butter, it turns a slimy glob into a fluid batter, but I don’t discount my water, maybe that’s why losing some water through steam has never been an issue.
    One other thing I do is to put it in the freezer, that way I can take it out in a couple of hours and do another batch using the same mold.
    Thanks for your tutorial, I might try the plastic again, maybe at a much lower temperature.

    1. Hi Marjorie – Try again with lower temps – when you combine hot oils and hot lye water you will get a volcano and if you want to avoid that, lower temps are the way to go.

  12. Wish you would of talked about knowing how much essential oil to add to soap. Soap Calc helped me out but it took a long time. Other than that article was PERFECT! Thanks

    1. That is up to you – it depends on how strong you want your soap scented. I tend to use 1 oz EO per pound of oils but that is just my preference.

  13. What do you suggest for vegan soap? the yogurt part I mean, is there anything else that will make the soap more fluid other than yogurt?

  14. Perfect hot process soap!
    I followed these instructions first spotted on the Ridgeway Soapworks website and since then my hot process soap has been smooth and trouble free. Using plastic wrap in place of the crockpot lid makes for a more fluid batter to the point where I can use some of my more intricate molds.

    Great work Molly, many thanks!!

  15. I have begun to focus almost entirely on hp soaps as I’m really getting tired of “feeding the lye” all of the expensive colors and scents in cp.

    I have gotten quite good at making it, but only after I set out on my own mission to figure out why hp always ended up so dry for me. As you mentioned in your article, “leave the lid on!” Is the most important advise to give a soaper struggling with dry hp. Go Sharon Johnson!!
    Last night I had a perfect, textbook cook. I was so excited that I actually took pictures of it. The only difference was that I began my cook at between 170-180 and yes I did have a very remarkable volcano 😉 Once I stirred it down, it progressed nearly perfectly.
    I am just about to cut my vanilla scented, cocoa colored double coffee soap, which nearly caused a stampede when I last sold it.

    I so wish that everyone could read this article before they ruin a batch of hp.

  16. Hello Molly,
    I don’t have a crock pot and want to try making hp soap. Is there a way to do it on the stove?

    1. yes, there are soapers who cook on the stove. I actually don’t make soap in a crock pot anymore because I make batches way bigger than a crock can hold. I will talk more about how I make soap in a future post, but I make soap using Sharon Johnson’s method which she clearly explains in her ebook. Check out the FB group Hot Process Soapmaking with Sharon Johnson if you want more info on how to make HP soap without a crockpot.

  17. Hello Molly,

    I tried your technic on the stove and it was better than I expected: The soap was fully gelled and I left it in the mold to finish the process. However, after adding my coffee ground before molding it ( temperature was around 82C) my soap was incredibly oily and greasy, and I cannot explain why. Every step was respected and I put the right amount of oils (I use the same recipe in CP and the results is very good). Is it something expectable when using the stove? Have you ever experienced it?
    I used in my formulation: 40% shea butter , 40% olive oil and 20% coconut. No SF.
    Maybe I am too impatient, I’ll let them dry for 1 or 2 days and see the final results.

    Thanks again


    1. Hi Mouna,
      I don’t add coffee grounds to soap very often, however, one time I had a very similar experience to you. I would suggest trying that same recipe and technique again but without the coffee to see if that is the issue.

  18. I am eager to try this method, but have always been unsure of the water amount, when I make CP I use 28%, so for this method should I go to 38
    Thanks Kerrie

  19. So much great information! I’ve been looking for info on keeping a bit more fluidity. I actually love the rustic look of the only HP recipe I make, so lumpy doesn’t bug me, but getting it from crock to mold can be almost anxiety producing! And I want to avoid air pockets I sometimes get because the batter gets a little too lumpy and unruly. Is there an order to adding the yogurt and EO? I need to crank up my production significantly, (problems of abundance) and thought about moving up to a big electric roaster, or something. I need to go from 6# batches to 12 or 18# , maybe (fingers crossed) even larger. Any suggestions for what type of cooking vessels I can use?
    Thank you so much for sharing your knowledge and experience.

    1. Hi Kerry! After my soap is cooked and cooled to <180F, I add my superfat, let it sit for a minute, then add my yogurt / sodium lactate. Then I split my batter for coloring and add any fragrance last. I cook my soap in large stainless steel pots. Happy soaping!

  20. Just wondering about orange/yellow spots and what causes them! I had cured my hp soap for about 4 weeks or more, I then put them in a plastic bag that seals and put my label on. Thinking sealing the soap made the spots that did not appear at first but later, a few weeks or more, did appear on a few then more bars! I cannot find much info on this except one soap group said Olive oil! I am wondering Your thoughts on this!? Thanks and I have just joined and the Reading so far has been most helpful! I have been soaping for over 1.5 years and love the hp process! Not that often because of time!

  21. Hi. Great article. When do you recommend I add dry add-ins to my hot process soap? I need it to be fluid enough to add in the dry stuff and still be able to stir it. HP can be so darn thick . Any recommendations? Also, thank you for your great website. I really do appreciate the helpful information.

  22. I have made 5 batches of soap they have ALL turned out to badly. In other words they all turned out to soft to take out of the mold. I did use beeswax the first time i made soap so i had to heat up the oils a lot hotter than i would have had to if i hadn’t used beeswax. But in my latest batches I didn’t use beeswax and the same thing happened. every time i add the lye it ether immediately gets so thick I cant use the stick blender or it take FOREVER to trace and instead of tracing it separates there’s always this weird grainy stuff on the top and melted oils underneath after what seems like eternity its will start to thicken up but its like mashed potatoes except is smooth and instead of cooling down is heating up with out me doing anything to it except stirring! I then transition to a wooden spoon and after continuing to stir it turns shiny and more fluffy which is usually when i put it in the mold because it looks like extremely thick patrolium jelly so i assumed it was ready. I have researched this but i cant find anybody who has had this problem. I have tried different recipes i have done hot process but when i try cold process it never traces it just immediately gets to thick to work with. I have researched on how to re-batch but I’m not sure whats wrong with my soap. I did read that if your soap is soft you ether didn’t add enough lye or you didn’t add enough water. I REALLY REALLY REALLY need some help so if you have any tips or advice i would love to hear from you!

  23. Ok…so I tried this and then as soon as I added the lye it seized. It seems to have gone straight to the Vaseline stage. Can I salvage it? And what do you think I did wrong?

    1. HHmm, the only time that happened to me was when I tried to do too big of a water discount. if you try soaping at 38% water, you should be fine. good luck!

  24. HI Molly, (wanting to do HP from the start) I came to your site after a failing first time try at soap making from another site. The other site did not mention anything about the temp of the oil before adding the lye. My first batch seemed to be seizing, like the lye was leaving the fats after over two hours in the crock. This was a tallow/coconut soap. Granted, I may have mismeasured the coconut. A handbook I have said seizing was a result of too much lye, or high temp of oil. The latter is what brought me to you. You are more thorough in directions, yet one more thing: Using the same recipe as the first one I tried being very careful of weight, and following your temp/saran wrap directions, I went 50 minutes without stirring (had a small volcano 10 minutes in, knocked it down). 1) Things looked better at 50 minutes, but there seems to still be a touch of oiliness bubbling. When I stir it it mixes in, but still some “seeps out” is this normal? 2) my Low on my crock puts the oil above 180…I ended up cooking on the “warm” setting. I think this is why my first batch failed…this ismore of a statement than a question. No websites seem to address crock pot temps…

    1. Hi Barb – Separation can happen in HP and the best thing to do is stir back to emulsion. I actually make batches these days that are way too big for a crockpot so I have not used a crock much in the past year or so. I do monitor my temps though, and soap cooks quite well in the 180-190 range. After a point my soap does go above 200 which is fine. One issue with crocks is that they don’t heat evenly which is why some people feel the need to stir. However, your soap (provided you used a good soap calculator and measured correctly) will cook eventually, so don’t stress about the exact time. Just try to avoid it getting dried out. Hope this helps!

      1. I have a few ???? https://www.modernsoapmaking.com/hot-process-soap-in-a-crockpot-tutorial/Hello I got through trace just fine, then when the 15-20 min on low crock cooking after trace my room got full of fumes. I had to go 2 times 2 the ER due to inhalation of fumes my nose, face ,throat burning diahrrea nausea my lungs felt they gonna explod. I had to stop the process . I put my crock pot still with the soap in it on the balcony and its cold outside here in Pa. My room been with the window open n I still smell the residue of the lye. can I save the batch unfinish hp soap its hard cuz its cold outside. Can I remelt it n just make it cold process to salvage it or can I continue to make it HP even tho I stopped the process 2 days ago?. it was a huge batch but Im concerned what went wrong . No 1 every said on videos it would fume up during hp cooking. Its only been mentioned it would fume during the mixing of lye with the water and it never fumed when I mixed lye to the water. I did that with no problem I did it outside with distilled ice chips and ice water in a basin under the bowl of lye water temp never went pass 89f. so I heated water in microwave I put the water in the basin to heat lye water to 112F n the oils was 138 was taking to long to come down so took some oil out of the crockpot put it in the freezer to bring to 114F then went on to make trace after the trace cooking it bot 20- 25 min stirred it and the horrendous smell of fumes in my bedroom. open my window but I has to go in n out my room to pick up n clean stuff I used to make the soap. while constantly breathing in fumes. I had to clean it up before going to ER cuz I have many grandkids come on daily basis . so I making the soap from 10:30 pm it was now 1:30 am went to er cuz I felt like I was dying. can this be saved and remade continue to try n cook it to hp or remelt it n try to finish it as cold process? n what did i do wrong cuz no1 ever stated it would fumeup during crock pot cooking n at that point I didn’t have on face mask or goggles help me I spent $400 in supplies to make soap . Options plz as Im very sick and cant afford to buy soap already made from suppliers I been buyn everythg for months to make my own soaps now I’m scared to turn the crockpot back on to see if i can finsih it after two days on the balcony in low temps. If not how do I dispose of it and is it still dangerous looked intot he pot today n it hard with some oils still there I touch it n smelled it . Then I got scared cuz I touched it with bare 2 fingers praying lye doesn’t get anymore into my body… Can I give you mu phone number or is there a phone number I can call you recipe used wasdouble it 4 oz castor oil 16 oz coconut oil 44 olive o oz 8.82 lye 21.12 oz water from I doubled it double it 4 oz castor oil 16 oz coconut oil 44 olive o oz 8.82 lye 21.12 oz water https://www.youtube.com/watch?v=scokYOkLcQo thank you Nancy

        1. Nancy,
          It really isn’t possible for us to thoroughly troubleshoot a recipe from another site with the limited info you gave, but I do see a lot of red flags in your process. I’d encourage you to read up on safe soaping before you think about making another trip to the soap pot: https://www.modernsoapmaking.com/make-handmade-soap-safely/

          These tips may help for the future:
          -Don’t forgo wearing a respirator
          -Don’t make soap in an unventilated area (It sounds like you were in a closed bedroom without any exhaust system.)
          -Be sure to calibrate your scale regularly. It’s possible your measurements were off, causing some issues.
          -Be aware that fragrances and other ingredients can cause negative reactions, especially without protective gear.
          -Use a check list/batch record to insure you add every ingredient correctly and don’t double up or leave anything out.
          -Use a reputable lye calculator to double check any recipe from any source.
          -Purchase supplies from a reputable supplier and check them against a spec sheet. Some lye has additives that aren’t safe for soapmaking and suppliers can make mistakes in filling and labeling products. A spec sheet will help you recognize mistakes.

          While we believe that just about any batch of soap can be saved, sometimes it just isn’t worth the investment of more time, money, energy, and, in your case risk. That sounds like the case in this situation. If you have no idea what went wrong, it is going to be hard to fix.

          Hope that helps, Nancy.

  25. Hi Molly: This is the most informative info I have seen and I have seen quite a long time. Everything you say about the soap finishing its cooking is right on. The internet is loaded with instructions that are not necessary and only confuse the beginner. Thanks a lot for sharing your wisdom and taking the time to set things straight. Lord knows we need more instructions like this !! Sometimes I believe incomplete directions are intentional. Not everyone wants to share their secrets !

    1. Bette I think you hit the nail right on the head when you said incomplete instructions are intentional! I am learning a lot from everyone posting here.
      Thanks very much!

  26. hello Molly?your soap making lesson is very interested to me.very along time i was searching on google,”how to make soap?”now you resolved my problem(question)about soap making.but i have an other question about soap creating.my question is this”what quantity of water,oils and lye inorder to have a complete soap done well?” thank you ver much for sharing with us your wisdom.

  27. Hi

    My name is Mona. I am a newbie to the hot process of making soap.
    I followed the steps you mentioned but my soap batch turned dark brown while it was being cooked. Have I overcooked it? Is it because I used a stainless steel pot? I didn’t take off the plastic wrap but still it turned dark brown.
    I also made liquid Castile soap in this stainless steel pot before and it turned dark brown . I don’t know where I went wrong.

    1. The only thing i know of that causes soap to turn brown is sugar added at too high of a temp (this includes honey & goat milk) or using a vanilla fragrance (but that does not usually happen right away). I make all of my soaps in SS pots. however, if there is a chance that your pot is actually aluminum, that could be the problem. good luck!

  28. Hi molly I did HP my liquids & oils were blended at like Trace at room temp and then added to a cold crock pot and I turned it on, when finished cooking letbit cool down to 180 and added cold extra’s and it all turned out fine 😊

  29. Do you have a recipe for HP soap with Coconut oil (about 50%), shea butter, olive oil, & sweet almond oil, or jojoba oil, with the lye & water, all in cup measures instead of weights? I find it difficult to get my head round weights for liquids (water & oils). My niece has made some with great success, but I have only ever made one batch of CP soap & I sailed into it without researching it all properly to start with. I did make soap, but it was rock soap! Made with just coconut oil, & used too much lye, so it was a bit lye heavy, but lathers beautifully & was lovely & white! I have bought a slow cooker too try doing it HP, like my niece did, but I am very nervous about getting my quantities right & I can’t use the lye calculator I found on google. Too long in the tooth & old in the head probably, I need it all spelled out for me.
    Thanks, Jocelyn

    1. Hi Jocelyn, I never make any products by volume – i do everything by weight. Volume measurements are not nearly as accurate, and with a product like soap, measurements are extremely important.

  30. Great website! I’ve used a recipe with olive, castor, sunflower, and coconut oil. It was a cold process recipe I got off another site that worked great. When I’ve used it for hot process the soap is a bit oily the next day. It eventually seems to dry out but is it ok to be oily for the first few days? It’s not covered in oil, it’s in spots. I’ve rebatched it and that gets rid of the oil, but I don’t want to do that every time. Does it just need a few days to cure?

    1. I would be very careful about recipes you find on online. I always run a recipe through a soap calculator to ensure that my formula is correct, and to my desired superfat level. I suggest you do that first and see if you have too much oil in your recipe. If you do not, you may have not cooked the soap for long enough. that is the only time i ever had a separation issue like the one you described. good luck!

      1. Thanks for the quick reply! I did check the recipe. And I cooked it to the Vaseline stage. But the rebatching would indicate that maybe I’m not cooking it long enough because it’s always dry once I’ve done that. Once it looks like the Vaseline stage I usually stop because I was afraid it would dry out if I overlooked it. But now I’m confused because you say you don’t worry if you haven’t cooked it enough because it will keep cooking once in the mold. I’ll check my numbers again too. It’s fun and I really want to get it right. I love the smell of the cooking soap! I could just do cold process but that’s not as much fun I think.

  31. Wow finally someone gets to the point and does not try to act as if they are trying to impress or write a book. Thank you for this post. Very good information. I have only done 4 batches of HP soap. They have came out good. I always wait to see vaseline look. Then I assumed it to be done. This made me feel more sure of my soap. I always wanted to ask just to be sure about – When it is done, flash point, and how hot is too hot. So discounting water doesn’t make it lye heavy? I have been lately adding a couple of ounces of water at the end to try and make it more fluid and cooler to add EO. but I see you said as long as it is 180 or cooler is good, sounds good to me.
    Thank you!

  32. If you don’t want to wait or your lye solution to cool or you want to heat your oils to a higher temperature, don’t worry!

    Can you spot the typo?

  33. Hello! Thank you so much for this helpful tutorial. I was wondering if the temperature you indicated for the completed soap (200 to 220) is an absolute. My first batch is reading 190 with my infrared and looks exactly like lumpy applesauce. I think I’m done, but when I did a zap test (yuck) I think I got zapped. 🙂 Any advice? I know you said it will continue to cook in the mold, but is that still the case if you don’t get to the 200 degree mark?

  34. hi, well, my first batches of hp soap was a disaster, lol. the soap never got “fluid”, when I put it in the mold, it was very chunky, had weird pieces of light colored hardened soap in it. after waiting overnight in molds, I took the soap out of molds and it crumbled. I have no idea what went wrong. I followed a recipe exactly. ??? I’m super bummed!

    1. oh no! that does not sound fun. your best bet is to take a bunch of photos and post in one of the hot process soapmaking groups. they are very helpful at troubleshooting.

  35. Hi, what is the typical shelf life of hot process soap with yogurt and/or milk additives? And can just about any cold process recipe be used in hot process soap? Thanks!

    1. because the ph of the soap is high, i have never had any issues with the goat milk or yogurt added to the soap. I believe any CP soap can be made HP (however, i certainly have not tested every CP recipe!). My suggestion is to make a small batch and see how it goes.

  36. Hi, I’ve only made melt and process and am completely new to any other soap methods. When you say you reserve the superfat (let’s say 5%) to add after the cook, do you mean: if I had 40oz of oil, then 40oz minus 5% equals 38oz, which is used for the actual cook. And then I calculate how much lye/water I need using 38oz with 0% super fat. The 2% of oil that I had reserved is then my superfat that I add after the cook? Sorry for the elementary question. Your tutorial is fantastic by the way!

  37. Hello! New here, great article! I have a question regarding adding the superfat once the soap is cooked. Say I wanted to add Mango Butter or Aloe Vera at the end, would I put it in the Soap calculator as a part of the recipe? Also how would that affect the superfat percentage in the calculator? I read another article where she had a very basic soap recipie (olive oil, coconut oil, water, lye – which is what I am going for) a 0% superfat and then added her superfat at the end but should I put that in the recipie calculator?

    1. I have only done a soap with a superfat that was additional oil over 0%. In other words, a 5% superfat where I add that additional 5% after the cook. I have made a 0% superfat soap however, i don’t add any additional oils after the cook. My concern with what you are trying to do is that there would not be enough oils for the lye to fully saponify. If you want to get the benefits of adding mango butter, i would suggest that you make a soap with all of your other oils in a recipe set to 0% superfat, and then add an additional 3% or so of the mango butter after the cook. hope this helps!

  38. dear molly thanks for the advise, the first time i tried the hot process was yesterday and it was not what i expected at all, as my soap came out all too foamy and did not thicken at all. my pot was filled and pouring over.
    i am used to the cold process so i just decided to try the hot process but it was a big mess.
    Please what could be wrong.

  39. Thank you! You answeres the exact question I was searching for; and you did it effectively and concisely! Thank you for this post!!!

  40. Hi Molly, thanks for a great tutorial. I just graduated from making melt and pour soaps and I am trying HP. I’m making shaving soap and I tried your tutorial today with my own recipe. My soap has the consistency of mousse rather than soap. I don’t think I cooked it long enough maybe? Other tutorials I have looked at says to cook the soap for 1 to 2 hours. I think I cooked it for like half an hour. I also didn’t keep any of the oil to ad in at the end. I didn’t realize the super fat refers to that. You see you have answered that question previously. I also ad activated charcoal to my soaps. When do you recommend to ad that in?

    1. I usually mix my activated charcoal with water, or if the entire soap is colored with AC, I will mix with goat milk & yogurt (or whatever you add after the soap is cooked). you could also mix it with your superfat.

      1. Great thanks, and then ad it after the cook when the oils have cooled a bit? Why do you think my soap came out looking like mousse, was it the cooking time? I bought a crock pot today so hopefully it would go better with the next batch 🙂

  41. Hi

    thanks for the very informative post.
    I don’t have a crock pot and I’d like to make hot process soap. Would you please do a tutorial on making hot process on the stove top.
    I have been trying but failing dismally. I just don’t know where I’m going wrong.


    1. Your best bet is to join the facebook group “hot process soapmaking with Sharon Johnson”. I use the method that she outlines in her book so that is really the best resource to learn how to make HP soap using a stock pot. good luck!

  42. Thank you for this tutorial. I wish I found it before I made my batch of HP. My questions are: at low my crockpot cooks at 125 and high at 185. Do I melt my melt my butters on low, then add my oils and allow it reach 125. After that add my lye water, stir to trace and continue to cook, covered on that low temperature. I find the temp number to be confusing. I wasn’t sure whether to turn it up after trace or to leave on low. I have seen so many tutorials and everyone has their own method. I just want to do it right. Thank you for your help.

    1. Never mind . I reread the article and realize the cooking process takes place on low, but you heat oils at a higher degree and add lye to that. I got it!

  43. Thanks Molly for your awesome tutorial 🙂
    I have always made CP but finally took a leap into HP. I made my first batch this morning and it went ok, not great but ok then I found your tutorial so I just did a second batch using the cling film and no stir method then added the yogurt and WOW what a difference! After warming all my utensils and essential oils the batter was so fluid it was super easy to work with and color. I used orange mica as I had a lot of orange EO to use up and threw in some poppy seeds just because I could 🙂 I used a basic OO, coconut, palm and castor oil recipe and it was lovely to use and gave great lather and conditioning while I was cleaning the utensils etc I can’t wait to get it out of the mold to see what it looks like 🙂 thank you again your tutorial really helped a lot 🙂

    1. Hey, Joan,
      Molly is actually teaching us a technique here rather than a specific recipe, which is awesome, because you can adapt it to the recipe of your choice!

      If you need help formulating your own recipe, here is a great post: https://www.modernsoapmaking.com/secret-to-the-best-soap-recipe/

      If you want to learn more about hot process in general, you can take a look at Molly’s other posts: https://www.modernsoapmaking.com/author/mollyelmore/

      1. I’m completely new to soap making and I mean I haven’t even made my first batch! Was thinking about using this process for my first time. So, that means that I just execute this process with any Cold Process recipe I find correct?

  44. So, I cold process soap all the time, however, I have had one problem that I’m hoping to correct. Maybe you can help.
    In one of my recipes I made the soap – thinking something seemed wrong – but went ahead and poured it in the mold. It never hardened – never. I made the recipe again – and again the same results. I couldn’t figure out what happened until I realized that I must have transposed the numbers when measuring out my lye, so never had enough lye.
    Not wanting to waste all of the product (of course, it was big batch) someone told me that it could be hot processed, yet no one can direct me.

    1. Hey, Teresa,
      I’m not a hot process pro, but, if you are confident you know how much lye you left out you may be able to create a lye solution (adding more water might cause some shrinkage during cure, but there is not way around it), mix that into your existing ‘soap’ batter (carefully!), and then hot process it.

      That said, you have to weigh the value of your time against the value of your ingredients, especially with such an uncertain outcome. And, of course, since you varied from your standard operating procedures, this won’t be a batch you can feel confident selling (if you are in business).

      Whatever you choose, I hope you have found your issue so you can get back to biz as usual making awesome soap!

    2. you could potentially rebatch, however, you would need to add more water to mix with the lye and that presents its own challenges. I suggest you chalk this one up as a learning experience and get your recipe perfected in small (1 lb) batches. good luck!

  45. I have been making CP soaps since 1989 and wanted to try my hand at HP. So, I bought a crock pot and did! Pretty sure I made some errors, crock pot on high, for example. Stirred it like crazy and let it sit a bit before putting the goat milk, superfats and fragrance in it. by then, the soap was hard where air touched it! I also discounted the water by 20% ( read somewhere else that would help it harden faster) So, maybe that was an error as well! NOW I need to go get some yogurt and try this again! Of course, NOW I have read thru your information here and want to try again.

  46. Hi Molly , I am extremely joyful to read about it.. I m an amateur trying hot process soap.. and I personally like it as it’s available to use at much shorter time . But I find a difficulty in this. I have tried two batches of soap. Each with 300grams .. but the issue is that fragrance doesn’t stay for long and I m determined to used only essential oil. I m worried to let it cool for a while as the batter gets harder. I do not know how to overcome this situation . And if I want to bring fragrance only through essential oils then what is the percentage that I should add to the batter which gives little more than the mild fragrance ?

  47. Thank you so much for this tutorial. Its really helpful. I did my first barch today and I did not have ph strips or a thermometer… so I did it until it looked a lot like the pictures you posted and everything seemed to be just fine. My question is, when do I know if I overcooked my soap?
    When I was putting it into my mold I felt it was very much … foaming? bubbly? is this normal?
    Thank you so much!

  48. Hi Molly,
    I really liked the information on website about HP soap making- I have tried CP and I have enjoyed the results. I have been reading up on the HP from several sites and when I was reading your advice on you site I was looking for information on making HP soap with used cooking oil. Is this possible to do ? Wanted to know if you or anyone who may have commented on your site had ever tried it. Was looking for HP way of using the used cooking oil.

  49. Hello,

    Thank you so much for your tutorial! I will try HP soap soon as I have a lot of soda ash with my CP recipe, and my soaps are not translucent. Do you think HP soap could fix my ash problem? Also, will the soaps be more translucent? Thank you!

    1. It’s possible that it will help with soda ash, yes.

      If you aren’t gelling your CP soaps, you will notice a difference in translucency. If you are, the difference likely won’t be dramatic, Julie

  50. This is far and away the single most useful and relevant article I have read on hot process soaping. As a professional cook of ten years’ experience, the quality indicators you describe here are invaluable knowledge for me, and have given me much more confidence to dive into hot processing. Thank you!

  51. Hi Molly,

    Thanks so much for this fabulous article. I am quite new to soap-making in general and have yet to try the hot-process method. After reading all the comments posted over the past two years, I’m definitely going to follow your method!

    Stretch-tite is unfortunately not readily available here in South Africa. Have you ever tried using one of the reusable silicone food wraps available these days? Do you think it might work in place of the stretch-tite?

    Thanks again for such a great article!

  52. Molly this was the best article I have read about HO soap. The plastic wrap makes 100% difference!!! I picked up one of those 3 crock pot buffet things at goodwill and am able to make 3 loaves at the same time! So cool! Thank you!

  53. Great article! You answered a lot of the questions I had after my one and only HP effort.
    Have you ever made soap in an instant pot? I have the ultra model and am able to custom set my temperature. Sous vide testers say the temps are very accurate and stable. This seems perfect for hp soaping. The pot is 6qt and stainless steel. What do you think?

  54. What a helpful post! The only thing I don’t understand is the part about ‘adding your superfat.’ I thought I understood this in my cold process methods but now I am second guessing everything! What does this mean in hot process soap?

    Secondly, can I take a cold process recipe and simply make it with a hot process approach or do some recipes only do well with one approach and vice versa?

    Thank you so much!

    1. With hot process, the soap mixture is near complete saponification before you pour it into the mold. So, many soapmakers like to add a specific oil after cook as their superfat. With CP, the saponification has just started when you pour it into the mold, so holding back a specific oil makes little difference.

      You can convert your CP recipes to hot process, Rhiannon.

  55. Pingback: Everything you need to prepare your own soap and the steps to make it at home | Web24 News
  56. Hi I am new to hotsoap process and i dont have a Crockpot
    May i ask if it is possible if I use a hotbath or a pan ontop of a stove
    If it is not possible i will buy a crockpot

  57. I have so much more confidence now after reading this article. I’ve made a few HP test batches but they weren’t the best. I think this next batch will be better based on what I just learned.
    Thank you!!!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.