Super Easy, Super Soap From Your Slow Cooker




Introduction: Super Easy, Super Soap From Your Slow Cooker

About: Mechanical Engineer, full time tinkerer and knowledge junkie.

As my culinary hero, Alton Brown would say, "The kitchen is no place for Unitaskers". While I would agree that the slow cooker is an amazingly flexible kitchen tool, making a great meal is the least of its tricks. I hope you will come along with me as I show you how this amazing tool can also make simple, top quality homemade soap!

Now with soap being readily available and relatively low cost at most all retail outlets, one would have to ask why make your own. Well, for starters the majority of soap available is mass produced with the lowest cost materials that can be globally obtained. Then the soap base has most all of the naturally occurring Glycerol extracted and sold as the main ingredient in skin moisturizers. Dyes, additives, and tons of perfumes are then crow barred into the product to make it look and smell appealing enough for you to use. What is even scarier is that the majority of what you think is soap has to be labeled and sold as Bath Bar, because there is no soap in it at all, just a chemically stabilized detergent "Frankenbar". Just look at the label....... Yeah, lots of big words.

My son helped me to learn all about soap when we found out very early in his life that he was allergic to the perfumes and additives in most all of the commercially available "soaps". I did my homework and found that old fashioned recipes for soap work perfect in the Slow Cooker, and produce a high quality soap with no reaction on my son's skin at all. The soap has a perfect balance of cleaning power, skin moisturizing, and lathering properties that we all love. Best of all, it takes only three ingredients, basic kitchen tools, and a little heat.

Step 1: Be Safe

I need to mention that safety should be first and foremost in any project. This recipe uses Sodium Hydroxide Lye as one of the ingredients. Lye is a strong alkaline and will damage eyes and skin on contact, so PLEASE use goggles. You should also keep a spray bottle of vinegar handy to neutralize the lye in the event of a splash.

Step 2: Ingedients

THE INGREDIENTS........ yep just three (OK, four if you count the water)!

1) 2 3/4 Cups Water... just good clean water. If you have a lot of chlorine or other chemicals in your water, just use some bottled.

2) 3/4 Cup Sodium Hydroxide (Lye).... We use 100% lye drain cleaner available at the hardware store. Please make sure it is 100% lye. It should be small granules to keep the volume correct.

3) 5 Cups Canola Oil

2 3/4 Cups Coconut Oil

We use a mix of Canola cooking oil and Coconut oil. Don't get fancy. Your Slow Cooker will not care if they are name brand. The Canola helps moisturize while the Coconut cranks up the cleaning power.

Please visit for a one stop shop knowledge extravaganza on soap. Their recipe calculator is just flat out amazing!!

Step 3: Hardware

1) Measuring cups... 1, 1/2, and 1/4 cup will do.

2) Mixer... We use a cheap stick blender, compliments of Black Friday at Walmart. A hand mixer will work great, as well.

3) 5 Quart Slow Cooker... Nothing fancy, low and high level is fine.

4) A couple of large plastic cups... Cheap and simple is the key.

5) Silicon soap mold... Optional I got this one from Ebay for a couple bucks but a bread or cupcake pan lined with plastic wrap will be fine. Heck, I once used a Pringles can and it worked fine.

Step 4: Mix the Water and Lye

Measure out:

3/4 Cup Lye in one cup

2 3/4 Cups Water in another large plastic cup

Slowly mix the lye into the water, stirring until all is dissolved. The solution will heat up, so let it cool while you prepare the oils. Never add the water to the lye cup.

Caution:Always add the Lye to the water slowly, stirring constantly until all is dissolved.

Never add the Water to the Lye.

The solution will heat up from the reaction (like hot tap water)

The solution will fume a little so always do this step in a well ventilated area and don't breathe the vapor.

Step 5: Prepare the Oils

Measure out: (directly into the Slow Cooker)

5 Cups Canola Oil

2 3/4 Cups Coconut Oil

The Coconut Oil may need warmed up to pour easily. Just set the oil in the sun for a while and it will melt just fine. Use your mixer to break up any chunks until the oils are mixed and smooth. Do not turn the Slow Cooker on yet, just keep the oils at room temperature.

Step 6: Add the Lye/Water to the Oils and Blend

Now that your oils are ready and your Lye water is mixed and cooled, it is time to mix them in the pot. Get your mixer ready and pour the lye water slowly into the oil.

Use your mixer to blend it all together. The mix will go from clear to something that looks like watery vanilla pudding. Just keep blending and the mix will slowly start to firm up and thicken to something like a nice creamy pudding. This point in soap making is called Trace and it shows that the Lye water is breaking the oils down in a reaction called Saponification. In short, the lye is breaking the triglycerides in the oil into soap and glycerol.

Step 7: Cook the Soap to Finish the Chemical Reaction.

All you have to do now is let the heat from the Slow Cooker finish the chemical reaction and fully convert the oils and use up all of the Lye.

Turn the pot to high until it starts bubbling around the edges. Give it a good stir, making sure to mix the clear glycerol that comes to the surface back into the mix. The glycerol is the good stuff that keeps your skin moist and protected. Keep stirring every 10-15 minutes to work the heat around and keep everything mixed. The soap will bubble and cook while slowly getting thicker. After 2 1/2 to 3 hours, the soap will have thickened up and look waxy. Your soap is now finished. All that is left is to form it and cool it.

Step 8: Form, Cool, and Cut the Soap.

While the soap is hot, spoon it into your mold. When you have all of the soap in the mold, give it a couple of good smacks flat on the floor to work any air bubbles out and even everything out. Let the mold cool overnight to set the soap solid.

When cooled, all you need to do to finish the job is pop the soap loaf out of the mold and cut to size. We use a rectangular silicon mold from Ebay and cut the loaf into 1 inch bars. (about $13 shipped)

Your soap is now ready for whatever mess you have to clean. This base recipe has no scents or oils added but the sky is the limit to what you can add. Additives can be stirred in to the cooked soap just before it is spooned into the mold. Most major grocery, pharmacies, and health stores have essential oils that you can add for scents. Keep it simple with these oils. They pack a punch, so less is best when exploring them. Usually 1 ounce or less of these essential oils will give the desired effect.

Here are a few additives we have tried with great success.

  • Finely ground coffee grounds - This adds a little scrubbing action for dirty hands or skin exfoliation.
  • Lemon oil - A bright clean scent
  • Spearmint oil - Sweet and fresh smelling
  • Peppermint oil - A cool, eye opener for a morning shower
  • Jewelweed - Poison Ivy soap, and yes, it works GREAT
  • Citronella oil - Bugs-be-Gone!

Step 9: Enjoy!

So, there you have it. Homemade high quality soap that you stewed up in your Slow Cooker. The bars are good to use immediately but as they dry out you will find that they last longer. Pop them into a paper bag for storage.

You will also notice that each batch makes a bunch of soap for the little money you have invested. Knowing that, you can now make really great Christmas gifts for very little cash that everyone will love.

I hope you learned something that will enrich your lives.

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28 Discussions

Can this soap be used straight away or does it need to sit for a few weeks to cure?

1 more answer

I let mine sit a few days and then use it. Doesn't take long.

Hello Drew,

I have made two batches of soap from your instructions. I've been wanting to make soap for years and you made it possible, and everyone who has tried it loves it! Thank you. My question though is in the cooking. You state that once you put the lye water into the oil to turn the crockpot heat to 'high'. However you make no further instruction as to how long one should leave the heat on other than until it's boiling. In my case I turned it to low once boiling however both batches were seemingly 'done' after an hour of starting with the lye water. It had the waxy appearance you specify and was very 'firm'. The soap turned out fine, but how did you manage to get your to go for two and a half to three hours?

We tried this yesterday and everything seemed to go great. Love that the soap did not have to mature weeks afterward before we could use it. Letting soap harden for a while befoore we cut it but I have gathered some crumbs together and washed my hands with them. Did a good job cleaning my hands. One thing we tried with I am a little worries about is that we tried to add some essential oils to the soap mixture at the end just before putting soap into molds. The fragrance doesn't seem very strong at all. How much essential oil should we put in a batch of this?

1 reply

I usually start with one ounce of oil per batch and adjust on the next batch. The oils are VERY potent and if you add to much you'll be bleeding out of the eyes for a while. If the oils are for therapeutic purposes, they will still do a fine job at lower levels. Go get'em!

It would be safer to use a solution of baking soda instead of vinegar to clean up a caustic spill. Mixing acid and caustic generates a lot of heat and could actually splatter.

2 replies

The idea of using vinegar (aka acetic acid) is to neutralise the sodium hydroxide

Sodium hydroxide + acetic acid = sodium acetate + water (both of which are non hazardous).

As a chemist, this would be my choice of acid for neutralising sodium hydroxide in this environment. It is, however, important to was the area with lots of water afterwards.

You would use baking soda (sodium hydrogen carbonate ) - a base - to neutralise an acid.

Stick with food grade vinegar and you will be fine.

Nice Instructible! One thing to note is that your slow cooker insert may become etched. We now have two slow cookers in my house as my wife did not take kindly to the state of ours after a few batches of soap.

I love making soap, however I'd hate to have anyone be hurt! In the MATTER OF SAFETY a splash of lye can burn right through skin and permanently damage an eye (as it is strong enough to dissolve human tissue) Gloves should be worn, arms covered and goggles to protect eyes. It's very easy to have the immersion blender sputter out sometimes - ouch. The lye will heat the water to extremely high temperatures so make sure the mixing container is high heat safe.

1 reply

Dilute NaOH is dangerous, but it isn't Lava. A splash on the skin will not even leave a mark if sprayed with vinegar as stated (I have plenty of personal experience in this area). The NaOH will damage eyes, so making sure that goggles are on is a must. Also, if the Lye is mixed in the quantities listed, the reactive heat will get to the area of 150-180 degF. Any plastic cup that is dishwasher safe will be fine in this situation. Don't get me wrong, I am all for Safety. I just want to avoid scaring potential Makers. Hope this helps.


2 months ago

This will be in my todo's a pretty long list :-D

1 reply

Go ahead and move this one to the top. It's high return factor on the time spent. Go get'um!

Thank ewe for this really helpful recipe. I would like to roy it with our goats milk. Dumb idea or do i do things differently? We have finished with all the bummer (extra lambs on bottles) so have lots of extra milk.....even the dogs leave a cup or 2 in Thier bowls after I pour in a gallon for the 5 of them!

So, is there a way to make this in slow cooker using goats milk & if so what is recipe



2 more answers

Goat's milk is my most favourite thing to add to soap! But you will need to change how things are done. It is similar to this but since the goat's milk has a lot of natural sugars in it it will need to be kept cooler when mixing or the lye will actually burn it (it will turn brown) I have a tutorial here:

Soap making is a wonderful thing and the possibilities are endless

Gotta love making soap! There is a world of oils to make soap with and although canola has some nice feel it tends to not last long due to the rancidity factor. 'DOS', (dreaded orange spots) will tell you that it has turned rancid. Olive is a wonderful alternative but should be put through the calculator on 'soapcalc'


2 months ago

Very nicely presented and documented instructible, with good photos throughout.

Most soapmakers use and measure all their ingredients by WEIGHT, not volume, so as to avoid a caustic soap that's harmful to the skin (by purposely "overfatting"). Would love to see how your recipe compares when computed by weight.

1 reply

Yes, making soap by weight is recommended as the calculator gives weight to the decimal point. Double check by doing the 'zap test'. I like to superfat my soap as much as 10% (see soap calc)


2 months ago

I suggest you use oatmeal instead of coffee grounds to add a bit of grit, it is a common ingredient is artisan soap.