12 Steps to Better Hot Process Soap

For the past few months I have been focused on hot process soapmaking, and have learned a few lessons along the way.  I am still learning, and the suggestions in this post are simply things that have worked for me in my quest to make better and better soaps! What do I mean by a "better" soap?  I want to be able to make swirled designs in my soap, which requires a fluid batter.  I want a hard bar of soap that lasts a long time.  I want a soap that does not crumble ever, especially when taking it out of the mold.  I want a soap that retains its scent.  I want a soap with no bubbles or air pockets.  I want a soap that moisturizes my skin.

Hot process soap made with fluid batter
Hot process soap made with fluid batter

Why don't I make much soap via cold process like I used to?  Because I really like a few things about HP that keep me attached to my crockpot.

1. No worries about fragrance accelerating trace, or heaven forbid, ricing

2. The clean-up is 100 times faster and easier

3. Less morphing of colors and no worries about gelling / not gelling / partial gelling / overheating during saponification

4. Soaps can sometimes be fully cured in 2-4 weeks vs. 4-6 for cold process

5. Control over what oils are the superfat in my soap

6. No ash on the top of my soap

Hot process soap where batter was very fluid
Hot process soap where batter was very fluid

Okay, now onto my tips (they are not in any kind of rank order).  By the way, most of what I am sharing here, I learned from other far more experienced soapers.  Please do not interpret this list as my original ideas at all.  I am just trying to put together a concise list for others to learn from.  My HP experience is based on the crock pot method of making HP soap so these suggestions for the most part apply to that technique.  There are other ways to HP - via oven, microwave and even just using your stick blender with hot oils and lye water.  I have not yet tried any of those methods so I can't speak to them.

1. Don't stir.

I used to stir and I really understand how after a lifetime of cooking food, the temptation to stir your soap is strong.  The reason I don't advise stirring is that it is not necessary and you will let a lot of moisture out which will make a fluid batter more difficult to attain.  I used to think that I had to stir for the soap to cook evenly.  I don't think that anymore, and I wait to stir until my soap is nearly done.  Photos here if you want to learn more about my method and when I stir.

I also like to cook on low.  The few times I tried to rush the process and cooked on high, things did not go well.  The soap cooked too fast, volcano-ed out of the crock and made a huge mess.  I am very careful to not let my soap get over 200F and that is much more challenging when cooking on high.

2. Make a leak-proof seal on your crock pot.

Best way to do this is to use plastic wrap.  I learned this from Sharon Johnson via her method that she calls Ditch the Lid.  One advantage of this method is that you can see the soap as it cooks without having to lift the lid.  Prior to learning Sharon's way, many people suggested putting a wet towel under the lid which helps preserve moisture, however, you still need to lift the lid to see how the cook is progressing.  Because not all soaps will cook at the same rate, being able to watch the cook is a great way to ensure that you don't overcook the soap.  You can also measure the temp using an infrared thermometer through the plastic wrap.  Another of the many great tips I learned from Sharon.

Checking the temp of the soap during the cook
Checking the temp of the soap during the cook

Some people may make a case for adding more water to the batter to compensate for evaporation that occurs when you lift the lid and stir.  That is definitely an option, but it would be so much harder to figure out.  I have no idea how much water escapes via steam when I open the lid.

3. Don't use liquids with sugar for your lye water unless you are OK with the soap turning brown.

This includes goat milk (or other milks), honey, wine and beer.  I make a rustic goat milk and oatmeal soap via HP and cook the soap using only goat milk as my liquid and this is the color (see photo below - no colorant was added to this soap).  It suits this soap but if I wanted a white soap, it would be difficult using this method because the heat caramelizes the sugar in the milk.

Goat Milk & Oatmeal Soap made via HP
Goat Milk & Oatmeal Soap made via HP

With HP you can hold back some of the liquid and add it after the cook.  This means that you don't use all of the liquid in the recipe to cook the soap, and add the remaining liquid when it is done cooking.  Example - recipe calls for 12 oz water.  You could cook the soap with 8 oz water and add the remaining 4 oz after the cook.  I have never tested the limits, but I believe that you should never use less liquid than lye when experimenting with this technique (i.e. if you are using 4 oz of lye, don't use less than 4 oz of liquid to make your lye water).

I made a soap where I added goat milk after the cook (photo below).  I colored the lighter part of this soap with TD (titanium dioxide) but it still is not white.  I think I added the goat milk when the soap was too hot and it still turned the soap a tan color.  Something to think about when adding goat milk to soap.  I will be more careful about the temp next time I do this.  Also - make sure you warm your milk.  Cold milk could make your soap harden up and become impossible to pour.

Soap with goat milk after the cook.  TD could not lighten it up to white.
Soap with goat milk after the cook. TD could not lighten it up to white.

4. Run EVERY recipe you create or find online through soap calc (or another reliable lye calculator).

Never assume that any soap recipe you find on the Internet is correct.  Always run it through a lye calculator.  This applies to all soap making, not just HP.  This tool will help you learn how each oil in contributes to the qualities in a soap (hardness, lather, cleansing, moisturizing).  This tool is your friend.  Do not be intimidated by it because it is a gateway to designing your own soap recipes.

5. Find hard oils that work for you

If you want a hard bar of soap that can be unmolded fairly quickly, hard oils are the way to go.  There are a few and they all bring different things to the party.  I like coconut oil, palm oil, tallow (when I can get it), lard and palm kernel oil.  Each of these have drawbacks for some people so you need to decide for yourself what kind of soap you want to make, and if you are selling, what is important to your market.  I aim for at least 60% hard oils in my soaps.   My favorite recipe has 65% hard oils.

What are the drawbacks to hard oils?  Well, some people don't want animal fat in their soap even though it makes a hard bar, is fairly inexpensive and in some cases, uses oil that would be discarded by meat processors.  Palm oil harvesting has caused widespread damage to the Indonesian rainforest and has had horrific consequences on the orangutan population, however, there are sustainable palm options.  Palm kernel comes from the fruit so it is more likely to be sustainable but I have no idea if similar damage has still occurred from this hard oil.  Coconut oil is a great oil for hardness and cleansing power, but it is expensive.  I have learned that a lot of palm kernel and coconut in the same recipe may lead to a drying soap (note the cleansing score).  You will learn this type of thing for yourself once you become friends with soap calc.

Can you make a great soap with primarily softer oils?  Yes, definitely.  But it will likely take longer to harden.

6. Get all of your additives together and ready to go before the cook is done


You don't want to risk your soap getting too cold because you are mixing up micas, weightng out your fragrance or searching your fridge for yogurt.  I am also much more likely to forget to add fragrance if it is not sitting right there with all of my other additives.  This will save time and make the molding process more efficient.

I get the following ready: colorants (I use both natural colorants such as clay and herbs as well as micas), yogurt / coconut milk / sodium lactate (I mix these together in a slurry to avoid clumps), fragrance and the warmed oils for my superfat

7. Add additives at the end of the cook to harden your soap, anchor your scent and increase fluidity

Harden Soap:

Sodium lactate is an easy way to make a harder bar of soap.  I add 1 teaspoon per pound of oil.  Some people add SL to their lye water.  I usually forget to do this so I add it with my yogurt slurry.

Anchor Scent:

I also use 1/2T ppo of kaolin clay to help anchor my scent.  This means that is helps prevent the scent from fading.  This can be especially important with some essential oils, like citrus eos, that fade quickly in soap.


Add yogurt.  This is another tip learned from Sharon Johnson.  This makes the batter considerably more creamy and fluid for pouring.  Check out my post on my soaping process for photos on the effect of adding yogurt.  I add 1T per pound of oil of full fat greek yogurt.  I also add 1T of coconut milk per pound of oil too but this is not needed for the creamy batter (aka a nice to have, not a need to have).  I also whisk my additives to a very smooth consistency because here is what happened the one time I did not.  I think this happened because the yogurt I like to use is quite thick.

note the brown specks
note the brown specks

I add the yogurt blend to the soap, put the lid back on and wait 3-5 minutes.  After that time (which I call the second mini cook), the batter is smooth and fluid.  I probably should discounts these additives from my total liquid, but I don't.  This is one of the reasons I use 38% liquid instead of the 40% that many other HP-ers use.

8. Warm your mold and mixing bowls

This helps with fluidity because if the batter gets too cold, it will thicken and be harder to pour.  I put my mold and bowls in the oven at 170F.

Note: tell other people in your family when you put soap stuff in the oven.  Last week, I put my mixing bowls and mold in the oven (it was off), left to run an errand and my husband decided to cook a frozen pizza at 11 am.  I will let you figure out the tragic death happened to the mixing bowls.  Amazingly, my silicone mold survived a visit in the 450F oven.

9. Let the soap cool before adding fragrance

I do not know if the ideal temperature is connected to the flashpoint of the fragrance, but some of the scents I have used burned off when the batter was very hot.  I believe the ideal temp for adding fragrance batter is somewhere around 150-160F.  I think that if your house reeks of the fragrance after you make the soap, the batter was too hot.  This happened the first time I made patchouli soap via HP and my husband made me promise to never make patchouli soap again.

If you would like to add honey, or even goat milk, let the soap cool or the sugars in those additives will caramelize and the soap will turn brown.  Premix honey with hot water to facilitate an even dispersal in your soap. Liz Ardlady advises to not add honey until the temp is <180F.

Even though the soap is cooling, and when it cools, it hardens, you have time to allow the batter to cool.  I used to worry that if I did not get the soap into the mold ASAP I could not be able to pour it or do swirls.  You have time to let it cool slightly and still swirl.  Don't leave the soap to do something else though.  I mix each soap to cool it down until I get to the desired temp.

10. Premix titanium dioxide to avoid white spots

If you only have time to premix one colorant, this is the one.  TD has a hard time dissolving evenly in oil (some people use water which I have not tried but you need to be sure your TD is water soluble).  If you premix in a bottle that you can shake, you are much more likely to avoid those dreaded white spots.  Some people put marbles in the bottle.  I did not have any marbles, but I had those glass bead things that you put in the bottom of a flower vase to help the stems stand up, so I used a few of those.  This is another suggestion that applies to all soap making and not just HP.  Feel free to premix micas too - this will save time and ensure that there are no lumps or clumps.

11. Don't expect the tops to be like CP

The texture is different and that is ok.  Embrace HP for its rustic awesomeness.  But the cake frosting like swirls that are on the top of CP - I have yet to figure out how to get there using HP.  I learned from Jami Summer to spray the tops with rubbing alcohol and it allows for more fluid swirling with a chopstick or wooden skewer.

12. Put the soap in the freezer before unmolding

Some soapers put their soap in the freezer right after it goes in the mold.  I can't do this because I use silicone molds that don't have a wood frame.  In the past, when I put hot soap in the freezer, it expanded on the bottom making it curved.  With my molds, it is best for me to let the soap cool and harden to room temp, and once it is a solid, put it in the freezer for an hour or two before unmolding.  For me, this leads to sharp corners on my soap.  I get very sad when the sharp corners from my soap stay in the mold after the rest of the soap has left the mold.

silicone mold
silicone mold

Please let me know if you have any tips that I can add to this list!  I am trying to give back to the incredibly generous soaping community that taught me most of what I know about HP.


Happy soaping!