Hot Processing Soap using the Closed-System Method

Do you love making cold processed (CP) soap but hate the wait of weeks before you can use your creation? Hot processed, or HP, soap is a wonderful way to use all the same ingredients you use in your CP to produce a soap that, like Melt and Pour soap, is ready to use as soon as it cools.

There are several different methods for hot processing soap. The oldest is direct-heat HP, which is what most people think of -- it means putting a pot of soap on the stove to boil, stirring it constantly until it gels and all the water is evaporated. This method is relatively easy as long as you can endure stirring for an hour and a half while wearing elbow-length rubber gloves, eye goggles, long sleeves and pants, and an apron. :) If you're like me, however, and aren't so fond of constant stirring, you might like using the closed-system method, abbreviated CSDBHP (closed-system double boiler hot process).

The CSDBHP method is relatively young. Its origins as I know them stem from one soaper adapting Catherine Failor's double-boiler gel acceleration instructions in her book Transparent Soapmaking to straight hot-process soap. If you can make CP, you can make HP using the closed-system method.



Safety equipment: goggles, gloves, apron, vinegar.
Double-boiler setup.

You should have one pot large enough to accommodate a doubled-in-size version of your regular soap batch, as the soap expands during heating. This pot must be stainless steel, glass, or undamaged enamel ware as it will be coming into contact with the lye. You should also have a larger outer pot that can comfortably fit your soap pot inside it with a firmly-fitting lid. There should be an object that the inner pot sits on to keep it from touching the bottom of the outer pan -- glass marbles, forks, small rocks, or tuna cans work well for that. It is important that your pots do not touch on the bottom, because if your inner pot comes into contact with the bottom of the outer pot it can scorch or burn your soap. I use a 20-quart stock pot for the outer pot and an 8-quart stainless steel pot for the inner, both with glass lids to help me resist peeking. :)

Heat source.

I prefer using a gas stove, but electric stoves and hot-plates work just as well.

Heat-resistant spoon or wire whisk.
Thermometer with glass or stainless-steel probe.
Soap ingredients: oils, water, lye, colorants, fragrance, and additives as desired.

The Process:

Stylistic Notes:

Transparent Soapmaking:

If you are comfortable with making CSDBHP, it's a very small step from there to making transparent soap from scratch. I highly recommend Catherine Failor's book Transparent Soapmaking if you are getting ready to branch into this fun variety of soapmaking, because she shares a great deal of information and tips, as well as offers many different recipes, in this book. You can purchase it from or many other booksellers.

To make transparent soap, you add solvents, such as sugar water, glycerin, and ethyl (grain) alcohol, to your soap at the end of the cook. You continue gently heating it until the soap is completely dissolved, and then your pour and mold it as usual. It's easy!

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