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Hot-Process Soap Making Adventures (With Recipes)

Rachel is a soap-making, wine-brewing homesteader and gardener in Minnesota.

Adventures in hot-process soap making

Adventures in hot-process soap making

Pros and Cons of Hot-Process Soap Making


Faster cure time

Limited ability to make affects such as swirls, shapes, etc.

Harder, longer-lasting bars

Process takes longer due to cook time

If you sell soap, you can make product available for sale sooner

More essential oil needed, sometimes

Making Soap

To make soap, regardless of the process you're using, you need three basic ingredients; leave out one of these ingredients, and you don't have soap:

  • Oil or fat
  • Lye
  • Something to dissolve the lye in, usually water

There are a few different ways to make soap: Full-boil (the most "old-fashioned" method, and also the common commercial method), cold process, and hot process. I've been making cold process soap for a while now, but recently, I learned to make hot-process soap.

In any process, a couple of things happen in order to make the soap. Lye is dissolved in water. Oils and/or fats are melted and heated up. When the lye solution and the oils are around the same temperature, they are mixed. The raw soap mixture must be stirred and tended to until it reaches a state called trace, which describes a pudding-like consistency and indicates that the ingredients are mixed properly.

The major difference between the methods is that in cold-process soap making, the soap is poured into the mold after the raw soap mixture reaches a state called trace. And that's it for cold process soap—you're pretty much done! The raw soap "cooks" in the mold, continues saponifying (turning into soap), and 24–48 hours later, you can cut it into bars.

But you can't use your cold process soap yet; you have to let it cure. Curing cold process soap can take three weeks to two months.

Kind of anti-climatic, don't you think?

In hot-process soap making, rather than pouring the soap mixture into the mold at trace, the soap is instead poured into a cooking dish (not metal!) and cooked in the oven at 180–200 degrees Fahrenheit for up to four hours.

Soap that is made using the hot-process method is fully saponified (totally soap!) after it hardens in the mold, and you only need to let it cure for a few days, just long enough for it to mellow out a bit and for what's left of the water to leave.

What to Do if You Get Lye on Your Skin

Don't panic! You'll probably first notice a slight itching sensation. You will not suddenly have a gaping hole in your skin! This has been my experience every time I've gotten lye or raw soap on myself. Here's what you do:

  • Douse the affected area with vinegar. This will neutralize the lye and turn it into a harmless salt.
  • Rinse the affected area under cold running water.
  • Wash the affected area with soap.

Soap Making Safety Precautions

Lye is sodium hydroxide, sometimes called caustic soda. It's the base agent in the soap-making process that turns oil or fat into soap. When all's said and done, your bar of soap won't have any lye left in it, which is why it's safe to wash with soap.

Historically, lye was produced for soap-making by leaching it out of the ashes of burned-up hardwood firewood. Some people still do this today. The rest of us probably know lye as a popular drain cleaner and opener. You can purchase lye at any hardware store and just about any grocery store. When making soap, you have to make sure that your lye product is 100% lye.

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CAUTION: Lye is a chemical that will burn you if it comes in contact with your skin, blind you if it gets in your eyes, and likely kill you if you ingest it.

However, people handle lye literally every day without killing or maiming themselves. They achieve this feat by wearing goggles, gloves, and long pants and sleeves, or other protective clothing like an apron. When working with lye, the trick is to avoid allowing your skin to come in contact with it. It's also not a bad idea to work with lye in a well-ventilated area, as the fumes that are released when lye is dissolved in water can smell bad and probably aren't something you want to breathe a lot of.

A great source for calculating soap recipes, including lye amounts.

"Another Lard-Based Soap"

  • Lard, 32 ounces
  • Coconut oil, 8 ounces
  • Crisco, 8 ounces
  • Castor oil, 3.2 ounces
  • Lye, 7 ounces
  • Water, 17 ounces
  • (3.2 pounds of oils)

"Vegan Soap (No Lard)"

  • Crisco, 16 ounces
  • Olive oil, 12 ounces
  • Coconut oil, 12 ounces
  • Castor oil, 2.4 ounces
  • Lye, 6 ounces
  • Water, 14 ounces

Now, on to the Recipes

The recipes! Here are three basic and very good soap recipes. I've used them all myself and continue to use them or some slight variation of them. For each recipe, you should follow the intructions for cold process soap making. Once the soap has reached trace, you will cook the soap in the oven at 180–200 degrees.

Check on the soap and stir it regularly, every 20 minutes or so. When the soap has reached a state that is like mashed potatoes, where you can see that portions of it are beginning to become translucent, and the whole mass of soap is very thick and stiff, you should stir it thoroughly again. It usually takes my soap 1 to 2 hours to cook. You can now press it down into the mold and let it cool (I let it cool overnight). Once cool, the soap is ready to cut and cure for a few days, then it's ready to be used!

(All measurements are by weight, not fluid ounces.)

"Simple Soap"

  • Coconut Oil, 12 ounces
  • Lard, 36 ounces
  • Lye, 6.8 ounces
  • Water, 16 ounces
  • (3 pounds of oils)