Soap Tutorial Part III: The Process

oil combo meltingIn Part I: The Components, we covered necessary and optional ingredients of soap. In Part II: The Recipe, we covered how to create a recipe and calculate the measurements. In this Part III, we cover the supplies needed, the technique and how to put it all together.

We’ve reached the part where you’re actually going to make soap!


In addition to the ingredients (castor oil, cocoa butter, olive oil, palm kernel oil, shea butter, distilled water, sodium hydroxide, salt or sodium lactate, sugar and essential oils), you will also need:

Long sleeved-shirt
Rubber gloves
Safety goggles
Crock pot
Kitchen scale
Plastic or wooden mixing spoons/spatulas
Containers for measuring things into (preferably heavy duty plastic)
Measuring cup to hold the liquid (stainless steel or heavy duty plastic)
Microwavable container for small amount of liquid to mix the sugar
Stick/Immersion blender with plastic guard (so it doesn’t scrape the enamel off the crock pot)
Small condiment container for mixing EOs with arrowroot powder
Mixing bowl to blend cooked soap with EOs
Soap mold(s)

The Process

The best way to explain hot processing (HP) is to compare it with cold processing (CP) and a hybrid called cold process oven processing (CPOP). I have done both HP and CP, with great results, but have not yet tried CPOP.

Cold Processing (CP). In cold processing, you bring your mixture to trace (the point of emulsification, explained below). Then pour it into the mold and wrap it in a blanket or towel to keep it warm. Saponification completes while the soap is in the mold. You unwrap and remove it from the mold the following day, cutting it into individual bars (if the mold didn’t already make individual bars). Then the bars cure until they are ready to be used. Methods of testing for readiness include pH strips, phenolphthalein or, literally, touching your tongue to the soap to see if it “zaps” (kid you not).

Things to note about cold processing:

  • There seems to be a greater need with this method to control for and correlate the temperatures of the oils and lye-liquid to each other at the time they are added together. I think the issue is that you are trying to keep all the ingredients as cool as possible so that the soap doesn’t get too far along the cooking process before you get it into the mold. As soap cooks, it goes through different stages and for cold processing you don’t necessarily want it reaching some of those stages before it’s in the mold.
  • Cold processed soap is generally in a fluid, liquid state when it is poured into a mold. Therefore, it is easier to mold and allows for more detailed, elaborate molds than can successfully be used with hot processing.
  • Any additives (EOs, clays, powders, colors, etc.) have to be added before the mixture is poured into the mold—which means before saponification is complete—which means they are going to be subject to that process. That can affect the scent, color or characteristics of some additives.
  • Even after being removed from the mold/cut into bars, the soap has to “cure” until it is safe to use.
  • If there is a problem with your lye ratio, you won’t know it right away. You won’t know it until your soap bars fail to reach the point of being safe to use (using one of these tests).

Hot Process (HP). With hot processing, there seems to be somewhat less need to correlate the temperatures of the oils and lye-liquid to each other before adding them together. You are going to be cooking them anyway.

You do still need to cool the lye-liquid. This is to prevent the mixture from getting so hot it overflows when you pour the lye-liquid into the oils. I cool the lye-liquid until the container feels cool to my touch. If you want something more scientific, aim for under 100 degrees Fahrenheit.

I also cool the melted oils before pouring the lye-liquid into them, but this is because I include sugar in the recipe. Sugar can increase the natural heat generated by the chemical processes. I don’t measure the temperature. I simply cool the crock containing the melted oils  in the same ice-water bath as the lye-liquid until the lye-liquid container feels cool to my touch.

Then I put the crock back into the crock pot base and add the cooled lye-liquid. Bring the mixture to trace (emulsification). Rather than pouring into the mold at that point, you stop stirring and let the mixture cook. It’s done cooking when the saponification process is complete at which point the soap is safe to use.

Again, you can use pH test strips or phenolphthalein for this. I always use the tongue test. I use a toothpick to remove a little bit of the mixture. Then (blowing on it first to cool it off a little), I rub it onto my finger until it forms a coating like warm wax. Then I touch that two my tongue. If it “zaps” like licking a battery, it’s not done cooking. If it doesn’t zap, but just tastes like soap, it’s done cooking.

Once it’s done, remove it from heat and mix in any additives. Then mold it. You don’t have to wrap the mold. The next day, remove the mold and cut the soap (if necessary). It is safe to use immediately, but it will get harder the longer it cures.

Things to consider about hot processing:

  • Once you’ve reached trace and stopped stirring, you still have to monitor this mixture closely. It can overheat and volcano out of your pot. If this starts to happen, don’t panic. Lower the heat setting or turn it off altogether. Use your blender to release some of the heat and blend it back down.
  • Sometimes, depending on ingredients, the mixture can be so hot it doesn’t need any heat applied and can just cook itself. (It’ll cool off when it’s done).
  • Even if it doesn’t volcano, the mixture will expand. Use a pot that is plenty big for your batch so that it has room to do this without overflowing.
  • You can’t really overcook it, so don’t worry about that.
  • When you remove the mixture from heat after the cook, it is going to be very hot. Some of the additives “take” better if the mixture is cooler—but the longer it cools, the more it hardens, making it harder to blend and harder to mold.
  • By the time you are putting it into the mold, it may well be the consistence of clumpy mashed potatoes. It does not pour into and accept the form of a mold as beautifully as cold processed soap. It has an entirely different look.

    Washing the dishes in the soap I just made with them.
    Washing soap making dishes in the soap I just made with them.

I prefer hot processing to cold processing for the following reasons. I like being able to blend in the additives after “the cook” (the saponification process) is complete on the theory that their beneficial qualities (for me, it is mainly the scent) survive better that way. I like knowing the recipe has “worked” and having soap that is ready to be used safely that day. I like being able to wash all my utensils in the lovely, warm, safe-to-use soap that I just made.

NOTE: I use a crock pot to cook my soap, but you could hot process soap in a double boiler or even a regular pot. I have never done either, so please do additional research before attempting.

Cold Process Oven Process (CPOP). I have never tried this one, but I will soon. In this technique, you bring the mixture to trace, mix in any additives, and pour into the mold(s), just like with cold processing. But instead of wrapping the mold in a blanket, you put it in a heated oven and let it cook in the mold for awhile. I guess you would need to make sure your mold is designed to withstand whatever heat you are using.

It is very much an individual preference. You will want to read about and try both. Also, there are other methods of hot processing that don’t involve a crock pot. But mine does, and this is how you do it:

Putting It All Together

This is before trace.
This is before trace.

Before starting, let’s talk about “trace.” Trace is the point when the oils, the lye and the liquid are emulsified. It’s an important “before and after” point in soap-making so you need to know what it looks like. Before trace, if you pull the blender out of the mixture, there is a smooth, unbroken surface. After trace, if you pull the blender out, it leaves indents behind in the mixture. Before trace, if you shake drops of the mixture off the bottom of the blender, they disappear immediately into the liquid. After trace, they will be visible on the surface for at least a little while before sinking back in. With that in mind:

  1. Measure your liquid into a container and put it in the freezer. It’s better not to let it actually freeze, but rather get right to the brink of freezing. Trying to mix lye into frozen water can be a pain. Remember to reserve (put into a separate container) a couple of ounces to use for the sugar water.
  2. Measure the oils/fats/butters into your crock pot. Turn the heat on and let them melt. I usually use the high setting.
  3. Fill the sink or a plastic tub with ice water. Add some vinegar and keep the jug of vinegar nearby for any emergencies.
  4. Measure the lye into a suitable container. Wear long sleeves, rubber gloves and safety goggles. Review lye safety rules here.
  5. When the lye water is on the brink of freezing, take it outside. Bring a plastic tub of ice water and vinegar or use a snow bank if one is available. Also bring a spoon or spatula (made of stainless steel, wood or plastic) for stirring. Take a separate trip for the lye so you can carry it with both (gloved) hands.
  6. Sprinkle the lye into the water—never the other way around—while stirring. You’re wearing your long sleeves, rubber gloves and safety goggles, right? Fumes will be emitted. Avoid breathing them in as you stir. Once the fumes are released and the lye is fully dissolved, you can bring the container back inside the house if you want or just let it continue cooling outside. Either way, it should sit in the ice-water bath or the snow bank as it cools.
  7. Keep one eye on the lye liquid as it cools. It is capable of creating a little, miniature volcano. This is most likely to occur when the lye is first added to the liquid and/or if you are using a liquid other than water. But it pays to be vigilant. Have it near a place where it can be dealt with quickly if necessary (i.e., poured down the drain or into the ground or tipped into your vinegar and ice water).
  8. Make the sugar water. While the lye is cooling and the oils are melting, use the microwave to heat the small amount of distilled water reserved for this purpose. Stir in the sugar until it is dissolved.
  9. Add the salt or sodium lactate. Once your lye-liquid container is cool to the touch, add your salt or sodium lactate and mix until dissolved.
  10. Pour lye-liquid into the oils. Once your oils are melted and your lye-liquid container (with the salt/sodium lactate stirred in) is cool to the touch, turn off the heat on the crock pot and pour the lye-liquid into the oils. Wear long sleeves, rubber gloves and safety goggles.

    This is after trace.
    This is after trace.
  11. Mix with the stick blender.  Some people do this in short pulses. I think this is to preserve the motor on the stick blender. I just go for it. Keep mixing until you reach “trace.” As explained above, you have reached trace when the blender leaves visible trails or tracks in the mixture and/or drops remain visible on the surface rather than immediately disappearing into the mix.Whether you turn the heat back on while you are mixing depends on a couple of factors. If the mixture is getting too hot (wanting to creep up and over the sides of the crock pot), leave it off. If the mixture is taking too long to reach trace, you might turn it back on to help speed up the process.
  12. Pour in the sugar water. Once you have reached trace, pour in your sugar water and mix well.
  13.  Let it cook. Stop mixing and set the blender down. (The mixture on the blender is probably still caustic, so set it on a paper towel or plate or plastic container.) Put the lid on the crock pot and turn the heat on low (unless the mixture seemed to get too hot when you added the sugar, in which case give it a little while to see how it goes before turning on the heat).
  14. EOs and Arrowroot. While it’s cooking, measure your EOs into a little condiment or sauce container. Blend in the arrowroot powder in an amount that feels Maybe…a couple tablespoons for this 5-pound batch…?

    This is the "mashed potato" phase of cooking soap.
    This is the “mashed potato” phase of cooking soap.
  15. Don’t stop watching it. If you stop watching it, is guaranteed to do this thing where it creeps up the side of the crock pot and spills out from under the lid and over the sides and all over your kitchen. If this starts happening, you will do any combination of the following to get the heat back down: 1) blend the mixture back down with the stick blender to release heat; 2) keep the lid off the pot; 3) turn the heat back off.
  16. Cooking stages. I have seen two different approaches to letting the soap cook. They are both fun in different ways. I have done them both. Both work. I’m not sure there’s any meaningful difference.
    This is the glossy mashed potato phase. I would start testing for doneness after this point.
    This is the glossy mashed potato phase. I would start testing for doneness after this point.

    The first involves setting a timer for say 50 minutes and watching for three phases. In the first, the mixture keeps wanting to separate. You will see clear liquid or clear oils separating from the rest. When you see that, use the blender to blend it back in. Keep doing that until it stops separating. Second, it stops separating and become a cohesive, mashed-potato-like mixture. Now it’s going to start expanding and getting fluffier as it cooks. Just make sure it doesn’t go over the edges. Third, it will being to look more like vaseline or like glossy, translucent mashed potatoes. When you hit the 50 minute mark AND reached the vaseline phase, test for doneness.

    It may be hard to tell, but there is a layer of clear liquid or oil on the top of this mixture. This is the "separation" phase. You can see how one side has started climbing the wall and falling back in on itself. If I had let it go, it would have eventually created an island around the separated liquid until it was swamped over, at which point you would blend and test. In this batch, I blended back together each time the mixture separated.
    It may be hard to tell, but there is a layer of clear liquid or oil on the top of this mixture. This is the “separation” phase that preceded the mashed potato and glossy phases in the two photos above. You can see how one side has started climbing the wall and falling back in on itself. If I had let it go, it would have eventually created an island around the separated liquid until it was swamped over, at which point you would blend and test. In this batch, I blended back together each time the mixture separated.

    In the other approach to the stages of cooking, you don’t worry about doing any blending during the separation phase or using a timer. Just leave the lid on and watch. The separated liquids will begin to move toward the center. Unseparated, cooking soap will rise up the walls of the crock pot and fold over onto themselves, thus surrounding the clear, separated liquids, which will become an increasingly smaller island in the middle. When that island is gone, blend the mixture for a little bit, recover and let it cook for another 5-10 minutes. Then test for doneness.

    Using either method, I am usually to the point of testing for doneness by the 50 minute mark, but it varies from batch to batch and this is just a guideline.

  1. Tongue-test. Check for doneness by using a toothpick to remove some of the mixture. Blow on it to cool it off. Spread it over a fingertip. Touch that fingertip to your tongue. If it gives you an electric zap like licking a battery, it’s not done. Cook for another 15 minutes and check again. Keep cooking until it stops zapping.

NOTE: If the zap freaks you out, keep a glass of milk at the ready. The milk will neutralize the lye. You can rinse your mouth out with it.

NOTE: If you’ve been cooking for over an hour with these ingredients and you’re still getting zapped, there’s a chance something has gone wrong. You may be lye-heavy. If it’s been two hours, it’s time to pack it in. Turn off the heat and Google for creative options to deal with a soap mess-up. You have my heartfelt sympathy.

In the mold.
In the mold.
  1. Remove from heat. Once it’s done zapping, remove from heat. Pour into a mixing bowl and let it cool for awhile (keeping in mind it will get progressively harder to mix and mold as it cools).
  1. Add the EOs. Sometimes I stick a thermometer down into the mixture so that I know exactly when the temperature falls below the flashpoint of my EOs. Remix the solution of EO and arrowroot to make sure it is well combined. Then pour it over the soap and mix in with a blender (probably a traditional blender; the stick blender won’t work well at this point due to the consistency).
  2. Pour into the mold(s). With hot processed soap, “pour” can mean more like scoop it up with a spoon and plunk it into the mold as best you can.
  3. Cool overnight. Have some wine. You deserve it.

    Remove from the mold the next day, slice and let cure to harden.
    Remove from the mold the next day, slice and let cure to harden.
  4. Remove from mold. The following day, remove it from the mold and cut it into bars (if necessary, some molds already have dividers). The longer you let the soap sit (cure), the harder it will get. But this soap is safe to use immediately.
  1. Enjoy. You just made your first batch of soap! Now start planning your next; it’s called a soap addiction.

For Part I: The Components, click here.
For Part II: The Recipe, click here.

2 thoughts on “Soap Tutorial Part III: The Process

  1. Pingback: Soap Tutorial Part I: The Fundamental Components | Hashtag Sarah

  2. Pingback: Soap Tutorial Part II: The Recipe | Hashtag Sarah

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