How to Rebatch Soap Using the Partial Rebatch Method
How to transform soap scraps, old soap, and failed recipes into beautiful new soap using the partial rebatch method. This method involves mixing soap shavings into a new batch of soap at a rate of 225 g (7.94 oz) of shavings per 575 g (20.28 oz) of oils in a new soap recipe. Together, they create a blended 800 g (28.22 oz) batch of recycled soap that contains 28% old soap shavings. Because the old soap used in this recipe was unscented, the essential oil rate is calculated for the entire batch at 3%.
Servings 10 bars
Cost 10
Equipment
- cheese grater or food processor
Ingredients
Grated Soap
- 225 g finely grated soap shavings From old fully cured CP/HP soap bars / 7.94 oz
Lye Solution
- 79 g sodium hydroxide 2.79 oz
- 158 g distilled water 5.58 oz
Solid Oils
- 144 g coconut oil (refined) 5.08 oz
- 115 g shea butter (refined) 4.06 oz
Liquid Oils
- 287 g olive oil (light colored or pomace) 10.12 oz
- 29 g castor oil 1.03 oz
Add at Trace
- 6.75 tsp lavender essential oil 30 g / optional
Instructions
Preparing to Rebatch Soap
- This recipe combines fully cured soap shavings from old soap with a new batch of cold process soap. Cold-process soapmaking is chemistry, and this recipe uses lye. Lye is a caustic substance that is completely neutralized during the soapmaking process, but it can be harmful if not handled correctly. Please read this soapmaking safety guidance before proceeding.
Grate the Soap Bars or Scraps Up
- Use the finest grid on a cheese grater to grate the old soap into the smallest pieces possible. If hand-milling soap is challenging, you can also use a food processor.
Make the Lye Solution
- Put on rubber gloves and eye protection (goggles) and set yourself up in a well-ventilated area. Near an open window or outdoors is perfect.
- Pour the sodium hydroxide into the distilled water and stir with a stainless steel spoon or silicone spatula. Be careful not to breathe in the fumes.
- Stir well and leave in a safe place to cool to 100°F (38°C). I usually set the jug containing the lye solution in the sink filled shallowly with cold water.
Preparing the New Soaping Oils
- If your recipe calls for solid oils, begin melting them on low now. I'm using coconut oil and shea butter in the example recipe.
- When melted, take the pan off the heat and cool on a potholder. Stir in the liquid oils from your recipe. Here, I'm pouring in olive oil and castor oil.
Blend in the Soap Shavings
- Add the soap shavings to the pot of warm oils. Stir well, then pulse them with the stick blender until very fine. This can take five to ten minutes, and you should give your stick blender a rest if it starts to feel too hot. You don't want to burn it out. You may get foam on the surface, but you can stir much of it down after you finish blending and before adding the lye solution.
- Keep blending the soap and oils until it cools to 100°F (38°C). You also need to keep an eye on the lye solution, stirring occasionally, and cool it to about the same temperature.
Make the Soap
- Get the soap mold ready, double-check that your goggles and gloves are on, and make sure you won't be disturbed for the next ten minutes.
- When the lye solution and pan of oils/shavings are both about 100°F (38°C), pour the lye solution into the pan of oils and soap pieces.
- Using the stick blender turned off, stir the contents of the pot together. Next, place the head of the stick blender against the bottom of the pot in the center of the pan. Turn it on and pulse for a few seconds, and then turn it off and use the stick blender as a spoon to stir the mix together. When the stick blender is on, it's best to keep it in one stationary place and to always keep the head submerged.
- You'll continue pulsing and stirring until the batter reaches a light-to-medium trace. This is when the soap begins to thicken slightly to the consistency of warm pudding. It can be a little difficult to determine whether the mixture is at trace with the soap shavings in the mix. A medium trace is easier to see because the soap batter will begin holding its form at the surface.
Add optional Soap Additives
- When the soap batter is at trace, stir in any additives such as essential oil or exfoliants. You could also add colorants, such as clay, at this point, but they may only tint the new soap batch and not the soap shavings.
Mold the Partially Rebatched Soap
- When the extras are mixed in, pour the soap into a mold(s). You can use loaf molds or cavity molds. I'm using this soap mold, which fits an 800 g batch pretty well. Insulate it or not, depending on the new soap recipe and preference. Leave to harden and cool for one to two days.
Cut and Cure the New Soap
- Remove the soap from the mold and cut the soap into bars if you've used a loaf mold. Cure the soap bars for four weeks before using them. This recipe makes about ten standard-sized bars and I've found that cutting with a wire gives the bars more of a textured feel than cutting with a knife.
- Once made, your soap will have a best-by date of up to the shelf life of the original soap shavings. It's determined by the best-by date of the original oils and ingredients used to make them.
Video
Notes
This method can be adapted to almost any cold process soap recipe. The ratio of soap shavings to new soap batter can vary, but it's not advisable to exceed 40% soap shavings to 60% new soap recipe oils, by weight.
Lastly, are you a beginner soapmaker looking for more guidance on making handmade soap? Enroll in the Natural Soapmaking for Beginners Online Course to get up to speed quickly. You'll learn all about soap ingredients and equipment and be guided through step-by-step soapmaking videos.