Soap from Glycerin

How to Make soap from your leftover glycerin.

This recipe is for glycerin made from biodiesel with LYE (aka sodium hydroxide or NaOH) and methanol. The creation of soap from the glycerin byproduct of biodiesel made with potassium hydroxide (KOH) is much different then what is described below.

The instructions below are being offered “as is” and the same terms and conditions (on the terms and conditions page) still apply. This recipe is only a guide, and you should use common sense whenever necessary. By reading further, you agree to no hold the owners/employees of for any liabilities from the information on this or any of its pages or within its videos. Always wear protective gear when working with these chemicals (i.e. Protective glasses, gloves, has-mat suit, body armor, etc.)

Sorry about the legal mumbo-jumbo above, we have to make sure that all of our assets are covered.

Well, if you produced nice, quality biodiesel (lean how by purchasing “Home-Brewed Biodiesel”, just click on the buy it now button on the left), then your glycerin should be ready to be made into soap. If you messed up, you might have made a big block of soap already, but hopefully you didn’t.

First, we need to remove any excess methanol as well as any little bits of nasty food or other items we “forgot” to filter out earlier. Start by staining the glycerin (you might need to heat it a little bit). You can use an old pair of pantyhose, a coffee filter (they take a while) or one of your 50 to 100 micron filters.

Next heat the glycerin over a hot plate (NO OPEN FLAMES) outdoors in a clear open area. Use a pot or container that can hold more then double the volume of the glycerin used (we will be adding some water to this later). STAY AWAY FROM THE FUMES. You want to bring the glycerin up to 150-170 degrees F. for a good 20 minutes. DO NOT LET IT SPLASH OVER ONTO THE HOTPLATE, otherwise fire and burns and all sorts of nasty things can occur. You, and you neighbors, don’t want that!

Second, we need to know the total amount of lye you used in the batch that the glycerin came from. If the number is on the lower side (say 3.5 to 5.9) use up to 39 grams of lye per liter. If you used a lot of lye when creating your biodiesel (anything about a 6) use 35 grams or less per liter of glycerin.

For example, let’s say that I used about 5 grams of lye per liter in my biodiesel batch. This means that I want to use about 37 grams of lye per liter of glycerin.

Let’s say that we only want to make 10 liters of our glycerin into soap, that means that we will need an additional 370 grams of lye. By the way, this would make a VERY large batch of soap. You might want to start with a smaller amount for your first batch. Also, if you are unsure of how much lye to use, check the PH of your glycerin. If it is very high, stay on the low side of the 35 to 39 gram scale.

Last, we need to measure out the water needed to create the soap. Measure out 25% of the volume of glycerin you are converting in water. In our example, we need to measure out 2.5 liters of water. Next, on a second hot plate, heat up the water to about 100 degrees F. Once it is up to temperature, CAREFULLY add the measured out lye (370 grams) to the hot water and stir it until all of the lye is dissolved in the water. DO NOT BREATHE IN ANY OF THE FUMES!!!

Next, add the water/lye mixture to your hot glycerin and stir while bringing the total temperature of the mixture back up to 150 degrees F. It might start to bubble a little bit. That’s okay, but if it starts to burn or boil over, crank down the temperature. Continue to mix it and hold it at 150 for about 20 minutes.

Turn off the hot plate. If you want to add any liquid scents, now is a good time to mix them in. Hold off on any “Solid” scents or decoration until you pour the soap.

Now pour the soap into a plastic container (there are some really nice plastic and Teflon coated plastic cake pans that are big and shallow that would work well for this, or if your are making a big batch like this one, use one of those “under the bed” boxes for clothing). Add any “Solid” decorations or fragrances (flower pedals, cinnamon sticks for the holidays, etc.). Allow the mixture to “set” for a day (24 hours), then flip the pan over and give it a gentle nudge. If all worked well, you should have a big block of soap (fit for a giant). Use a knife (carefully) or some piano wire on two posts (like a cheese cutter) to cut the soap into more manageable pieces. Allow the soap 2-4 weeks to cure. This allows the water to evaporate. Do not use the soap until fully cured. It may still be caustic and you should perform a ph test. The soaps ph level should be less then 10.

Making soap can be fun, and it’s a great way to recycle your byproducts. Don’t forget to use some sort of scent, otherwise your soap will smell like whatever was cooked in it (hey John, that new “Deep Fried Soap” scent your wearing is really attracting the ladies). If you want a more gentle soap, add a little bit less lye to the mixture when you are cooking it. If you want to make a more abrasive soap, add a little bit more lye when you are cooking it. Don’t add too much lye, or you might get so abrasive that it can take your skin clear off!! Try starting off small, and work your way up to bigger batches.

Remember to label all of your equipment and supplies “POISON” in order to prevent accidents. You don’t want anyone using your lye measuring spoon in their coffee. It would really ruin someone’s day.

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