Hot Process Soap Stages

How to Make Hot Process Soap

Hot Process Soap Stages

Reading Time: 6 minutes

Learning how to make hot process soap can be very rewarding, and it does have benefits lacking in cold process soap making. Hot process soapmaking creates a fully saponified soap before you pour it into the mold. No need to wait a day or so for the soap to fully saponify before cutting — as soon as the soap is cool, it is ready to unmold and slice. In this article, we will examine the hot process soap stages that you can expect to see as your soap cooks. Hot process soap stages are a good indicator of where in the process your soap is currently as far as completion. As you learn how to make hot process soap, you will come to recognize these stages in order to know when your soap is ready to pour.  

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Hot process soap has been fully cooked to saponify the oils before pouring into the mold. It produces hard bars of soap that require far less fragrance or essential oil than cold process soap. In addition, soda ash almost never occurs with hot process, even though full water is used. It may seem complicated with the many different stages the soap can go through, but it is really quite simple.  

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Hot process soap has a rustic appearance. This is normal. Photo by Melanie Teegarden.

Hot process soap stages include concepts such as “champagne bubbles,” “applesauce stage,” “wet mashed potatoes,” and “dry mashed potatoes.” Every batch is a little different, depending on your recipe, batch size, the heat of your crockpot and a host of other factors. You may notice some of these stages in your batch, but not see others. It is no cause for alarm. The most important things to remember about hot process soap making are to stick blend all the way to medium trace, then allow the soap to cook, stirring occasionally until the soap becomes consistently soft and fluid-like mashed potatoes. As for whether the “mashed potatoes” need to be wet or dry, the choice is yours. The soap is usually fully saponified by the time it is at the wet mashed potato phase. You can use pH testing strips to check if you like, but even if there is residual lye at this point, it will be used up by the time the soap is cooled and hardened. At the “wet mashed potato” stage, the soap is rather fluid and easy to mix and pour. The resulting soap is generally smoother and more similar in appearance to gelled cold processed soap. If you prefer, you can continue cooking the soap to the “dry mashed potato” stage, which will cook out some extra water and allow the soap to harden faster. The drawback is that this texture is harder to glop into the mold. There are often small air bubbles in the batter — bang the mold on the tabletop to remove as many as possible — and the tops are often rustic in appearance. One trick for how to make hot process soap smooth is to cook the soap all the way to the “dry mashed potatoes” stage, then remove from heat, add some yogurt (one ounce per pound of base oils) and stir until smooth before adding fragrance, color, and spooning into the mold.  

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Applesauce stage. Photo by Melanie Teegarden.
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Wet mashed potato stage. Soap is finished. Photo by Melanie Teegarden.

Hot Process Soap Troubleshooting 

One thing that can happen when working with soap at high temperatures is the “soap volcano.” When this happens, the soap begins to boil up and may even come out of the soap pot if not supervised and stirred down from time to time. A simple solution prevents a mess: place your crockpot into the basin of your sink before cooking your soap. Another problem, especially with a high olive oil content recipe, can be soap that is slow to trace. Since you will want a medium trace for this soap, sometimes the stick blender can overheat before the job is done. Simply alternate one minute of stick blending with five minutes of resting until the desired thickness is achieved. Finally, because hot process soap can be harder coming out of the mold, sometimes after 24 hours it is so hard that it must be cut with a knife instead of a wire slicer.  

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Stick blending to medium trace before the cook. Photo by Melanie Teegarden.

Other Hot Process Considerations 

You will need half as much essential or fragrance oil for hot process soap as you need for cold process soap. Each essential and fragrance oil has a different usage rate. Be sure to look this information up before you start. If you are used to working with a water discount, you will want to refrain from discounting water in hot process soap making.  

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Finished hot process soap. Photo by Melanie Teegarden.

Hot Process Soap Recipe with Yogurt 

  • 4.25 oz sodium hydroxide 
  • 7.55 oz water 
  • 2 oz plain, unflavored, sugar-free yogurt 
  • 20 oz olive oil 
  • 9 oz coconut oil 
  • 3 oz castor oil 

Wear your eye protection and gloves before you begin. Set a crockpot into the basin of a sink and turn on Low. Weigh the oils and add to the crockpot. Meanwhile, in a dry container, weigh the sodium hydroxide. In a separate, heatproof and lye-safe container, weigh the water. In a well-ventilated area, slowly pour the sodium hydroxide into the water, stirring to completely dissolve. Be careful not to breathe the steam that arises from the lye solution, which will dissipate quickly.  

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Melt oils in crock pot on low heat. Photo by Melanie Teegarden.

Pour the hot lye solution into the crockpot. There is no need to let the lye cool because it is going to get cooked, anyway. Mix well by hand until the solid oils are fully melted, and then begin stick blending until medium trace is achieved. Cover the crockpot. Check every 15 minutes to see if it needs stirring. You may see a stage called Champagne Bubbles, where the soap seems to separate and there are bubbles simmering in clear liquid. From this stage, it can move into the Applesauce stage, where the soap batter develops a grainy appearance, much like applesauce. This stage does not last long and you may miss it completely, which is fine. What you are looking for is a soft mashed potato consistency with a translucent quality to the soap. It generally takes between 1 and 1.5 hours for this to happen, but it can vary.  

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Adding mica mixed with oil to cooked soap. Photo by Melanie Teegarden.

When the consistency has reached that of soft mashed potatoes, the soap is technically cooked. Remove from heat, uncover, and let sit for five minutes to cool slightly. Add the yogurt and mix well. Add fragrance, if using (remember to use HALF of the recommended usage rate for cold process soap!) and colors, if using. Use a large spoon to scoop up the soap and glop it into the mold, banging the mold on the tabletop between layers to remove as many air bubbles as possible. Soap is ready to slice as soon as it has completely cooled. For best results, hot process soap still needs a curing period, just like cold process soap. While technically you can use your soap right away, it will be longer-lasting, have better lather, and have a gentler pH level if you allow it to cure for at least four weeks.  

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Finished hot process soap. Photo by Melanie Teegarden.

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