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. Involves mixing soap shavings into a new batch of soap. The soap scrap to new soap ratio is up to 1:2.5 -- that's the weight of soap scraps to the weight of new soaping oils. It can also be calculated as soap scraps being up to a maximum of 40% of the weight of the oils in the new batch. How much liquid you use to make the lye solution is up to you, but I'd advise not to water discount too much. I use a ratio of 1:2 lye to distilled water but you may wish to use more water. The recipe makes an 800 g (28.2 oz) soap batch.
Servings 10 bars
Cost 10
Equipment
- cheese grater or food processor
Ingredients
Grated Soap
- 225 g grated soap shavings From old CP/HP soap bars / 7.94 oz
New Soap Recipe
- 575 g Your choice of a new cold process soap recipe Amount refers to amount in soaping oils / 20.28 oz
Instructions
Choosing a New Cold Process Soap Recipe
- Cold-process soapmaking is chemistry, and this recipe uses lye. Lye is a caustic substance that is completely neutralized in the soapmaking process, but it can be harmful if not handled correctly. Please read this soapmaking safety guidance before proceeding.
- There is no specific soap recipe listed in terms of ingredients because that part is up to you and the soap scraps you're using. Simply scale your chosen recipe up or down so that it is a 575 g soap recipe. I have loads of cold process soap recipes to choose from here if you'd like to use one. Use a soap calculator, such as the SoapCalc to scale recipes up and down.
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. The amount of soap shavings to new soap base I'm using is 1:3.5. The easiest way to calculate that is 40% of the weight of the new soaping oils equals the weight of the soap shavings to use.
Make the Lye Solution
- For full information on soap-making safety and equipment please head over here. It’s important to read it before trying to make soap the first time. Put on your rubber gloves and eye protection (goggles) and set yourself up in an area with good ventilation. Near an open window or outdoors is perfect.
- Pour the sodium hydroxide into the distilled water in your recipe and stir with a stainless steel spoon. Be careful not to breathe in the fumes.
- Stir well and leave someplace safe to cool to 100°F (38°C). I tend to set the jug containing the lye solution in cold water in the sink.
Preparing the New Soaping Oils
- If your recipe calls for solid oils such as coconut oil, cocoa butter, or shea butter, begin melting them on low now.
- When melted, take the pan off the heat and cool on a potholder. Stir in the liquid oils from your recipe such as olive 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 begins feeling too hot. You don't want to burn it out. You may get foam on the top of the surface but you can stir much of it down after you finish blending, and before you add the lye solution.
- Keep blending the soap until the oils have cooled to 100°F (38°C). You also need to keep an eye on the lye solution, stirring occasionally, and cool it to around the same temperature.
Make the Soap
- Get the soap mold prepared and double-check that your goggles and gloves are on and that 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.
- 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 far better to keep it in one stationary place and to always keep the head submerged.
- You'll continue pulsing and stirring until the batter hits a light to medium trace. This is when the soap begins to thicken slightly to the consistency of warm rice pudding. It can be a little difficult to determine if you've hit trace with the soap shavings in the mix. Medium trace is easier to see since the soap batter will begin holding form at the surface.
Add optional Soap Additives
- When the soap batter is at trace, stir in any additives such as essential oil, colorants, or exfoliants. An explanation of how much essential oil to use is in the piece above. Colorants may only affect the new soap batch and not the soap shavings though there is further information on that above too.
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.
Notes
Lastly, are you a beginner soapmaker looking for more guidance on how to make 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 soap recipe videos.