The Beginner’s Guide to Soap Making – The Hot Process Method

The hot process of soap making is very similar to the cold process except for the best thing about it is that you won’t need to wait 4-6 weeks for your soap bars to cure! They’ll be ready to use right away! The soap will also result in a different, more coarse texture compared to cold-process soap.

This method is referred to as the “hot” process because you are using heat to actually cook the soap mixture to neutralize it.

It’s considered a more advanced method of soap making so I would only explore it once you have a good grasp of the other methods. You’ll also be using a slow cooker for this process!

You also will be working with lye during the hot process method. Lye can be dangerous and extreme caution is required to work with it.

Lye combines with a fat to form soap — this is called saponification. If you don’t want to work with lye, you can try to rebatch method or the melt and pour method.  In these methods, you’ll work with pre-made soap that has already gone through saponfication.

Want to learn more about soap making or explore other methods? Check out these other guides from our exploration of soap making as January’s hobby of the month:

SUPPLIES NEEDED

The supplies needed for the hot process are listed below. For specific information about these supplies, check out this guide to soap making supplies here.

  • Lye
  • Ventilated space
  • Rubber gloves, goggles, mask
  • Slow cooker
  • Water (distilled and tap)
  • Heat-safe glass containers
  • Stainless steel measuring spoons
  • Digital scale
  • Thermometers (2)
  • Silicone spatulas
  • Electric stick blender
  • Rubbing alcohol
  • Soap mold
  • Litmus paper

HOW TO MAKE SOAP USING THE HOT PROCESS METHOD

The cold process method of soap making will vary based on your recipe but generally you’re going to follow the basic steps I’ve listed below.

Always check with your recipe and always check the amount of lye you have in your recipe with an online calculator. 

If the ratio is off between lye and oil, the soap will not fully saponify and you may have lye leftover in your final product. Leftover lye is NOT good.

  1. Work in a well-ventilated space. Ensure you wear all your protective gear (rubber gloves, goggles, long sleeves, and mask). This is because lye doesn’t like to play nice.
  2. Measure out your ingredients. Remember, only use silicone, stainless steel and glass equipment when handling lye. Never use aluminum, cast iron, nonstick finishes, weak plastic or thin glass. Weigh out using a digital scale to get exact weights. The ratio of the ingredients will definitely make a difference.
  3. Add your oils into the slow cooker. Melt your oils together in the slow cooker. Do NOT overheat your oils so watch them closely.
  4. Fill a heat-safe container with water. Use distilled water when making your own soap. You never know what sort of contaminants you might find in regular water. Since you’re working with lye, you don’t want the risk of it reacting to anything you don’t want it to react to.
  5. Slowly add lye into water. Sprinkle the lye carefully into the water. Remember, water into lye will cause you to die, lye into water will make you smarter. NEVER EVER add water into lye. This can cause a very unwanted, terrible reaction. The lye solution WILL heat up so be careful. Once you have mixed the lye in, set it aside to cool.
  6. Use your thermometers to track the temperatures. Once the mixtures are at 110F, you will slowly pour the lye solution into the slow cooker.
  7. Stir the mixture. Since you are still working with lye, make sure you use only silicone, stainless steel or heavy-duty glass equipment to stir. Stir for about 10 – 20 minutes until you start to notice traces.
  8. Cook for 3 hours on the low setting. Check the soap every 30 minutes. Consistently check the neutrality of the solution with the pH paper.
  9. Add any additional ingredients. If you want to add any extra ingredients, make sure the mixture is neutral.  Also remember that the mixture will be hot so you shouldn’t add anything that might melt. Since glitter is plastic, it will melt when added at high temperatures. If this is something you want to add, make sure it’s mixed in when the mixture starts to cool down a bit.
  10. Pour the mixture into the mold. When everything has been evenly distributed, you can fill the molds.
  11. Let the soap cool before unmolding. If you used a mold that will result in a long log of soap, use a knife to cut it into bars.
  12. Use! Your soap bars are now ready to use! If you want to save it for later, store them in a ventilated container.

SPECIAL TECHNIQUES FOR HOT PROCESS SOAP MAKING

EMBEDDING

You can embed pretty much anything you want inside a bar of soap such as plastic toys, gemstones, or even silk flowers. Remember that certain objects can melt under high temperatures.

  1. Fill your mold halfway with your mixture.
  2. Generously spray your object with rubbing alcohol.
  3. Press your object into the soap mold but don’t press it so hard that it hits the bottom surface of the mold.
  4. Pour the remaining soap mixture to fill up the remainder of the mold.

LAYERING

Layering soap can create some pretty sweet-looking creations. You can get really creative with colors and shapes when you layer.

  1. Pour your first layer of the mixture into the mold. Let this layer cool but not so much where the whole layer is hardened.
  2. Spray the first layer with rubbing alcohol to allow the next layer to stick.
  3. Pour the second layer onto the first layer.
  4. If you want more layers, repeat the above steps.

SWIRLING & MARBLING

Swirling and marbling take a lot of practice! If you really enjoy soap making, you should try exploring this special technique.

Swirling is generally done by controlling the level of trace of the mixture and the way your pour it into your mold.

Since swirling can really only appear if you use different colors, pour at a thin-medium trace for a thinner swirl. Pour when the mixture is heavily traced for thick colors.

Use a toothpick to lightly drag through the mixture to create a marbling effect.

If you want to the whole bar of soap to have this effect, make sure to use a thin, marbling tool that will touch the bottom of the mold. Play around with this special technique to see what you can create!

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