How to transform soap scraps, old soap, and failed recipes into beautiful new soap using the partial rebatch method. It involves grating old soap bars and adding them in a certain ratio and method to new soap recipes. It’s an easy way to rebatch soap without a crockpot and will make your old soap new again!
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Every soapmaker has a stash of old soap that they’re reluctant to get rid of. It’s still good soap, but the color might be off, the scent faded, or the bars have dents or imperfections that make them unsaleable and un-giftable. Some soapmakers also bevel the edges of their soap bars or tidy up the sides with a cheese grater. Each batch creates a lot of soap scraps and chunks that are perfectly good soap but too small to use on their own. Fortunately, there are ways to transform old bars and soap scraps into new soap! The main way is to rebatch soap, but the old method that uses a crockpot is now being set aside for a new way – the partial rebatch soap method.
These easy instructions involve grating old soap with a cheese grater and incorporating it into a new batch of cold-process soap. The resulting bars are smooth to slightly textured in feel and have a gorgeous granite-like pattern, especially if you blend darker soap scraps into a light-colored batch of soap. I’ve also found that the design and look of the bars is far more professional than any other rebatch soap method you’ll find. So good that it looks planned from the start!
Explanation of Partial Rebatch Soap
The partial rebatch technique is what it says it is. Instead of making a new batch of soap completely of old soap, you instead make a batch that combines old soap with new! It uses the cold-process soap making method and soap shavings from previously made bars. Shavings from soap made with either the cold-process or hot-process methods are suitable for this project but avoid melt-and-pour. This is a soap making technique best suited for the immediate to advanced soapmaker. Beginners may struggle on some aspects but if you have a good grasp of cold process soap making then feel free to give it a try.
The first step is to grate up the old soap with a cheese grater or food processor. Next, you’ll make a new batch of cold-process soap and add the soap gratings to the mix. Then you’ll mold, cure, and use the soap as you would any other new batch of cold-process. This is a simple explanation of the process, and more detail is to follow.
Partial rebatch soap is an easy soap recipe, though, and there’s a lot of freedom to be creative! Read on to see how it all comes together with recommendations for amounts, technique, and colors.
Using Soap Shavings of the Same Color
One of the best ways to use the partial rebatch method is to transform old soap into a new batch of the same recipe. I did this recently with some old bars from my eco-friendly cold-process soap recipe that were a little banged up. By adding the shavings to a new batch of the same recipe, the pieces matched the new soap in color.
This works for soap batches of any shade or color, including those with natural soap colorants. If you had a few bars made from my pumpkin soap recipe, then you’d shave them and add them into a new batch of pumpkin soap. In most cases, the soap shavings will be seen as a fine speckling throughout the bars but be very close in color.
Colored Soap Shavings in a Light Colored Soap Base
The fun in partial rebatching begins when you start playing with different colors. I’ll go through a few different ways to use and add color, beginning with the easiest.
Soap shavings can have their own color, which can affect the final batch’s shade. That’s because the method involves stick blending soap shavings into a new batch of soap. If the shavings are darker than the new soap base then some of the color from the shavings can color the new soap.
For example, I made quite a few bars when I developed the indigo soap recipe. They were unscented because I was demonstrating how to use the natural blue color and I didn’t want to use conflicting ingredients. I prefer using scented soap, though! So I grated some of the blue bars up and added them to a batch of plain, uncolored soap along with chamomile essential oil and rose absolute for scent. The result was light blue bars of soap with darker blue speckles. I love how they look! It also shows exactly how the soap shavings pulse up and disperse in the rebatch soap bars.
Using Soap Shavings of Different Colors
One of the best ways to make partial rebatch soap is to use a mix of different colored soap shavings. That’s excellent news for those who have lots of soap scraps in different colors! Mixing multi-colored soap shavings into a new batch of soap shows up as colored speckles throughout the new soap bars. Effectively a sophisticated type of confetti soap since the pieces are small and better dispersed. If you have a good mix of colors — pink, blue, green — it can look like rainbow chip cake! Do be aware though that the darker and more vivid the colors are, the more likely that they’ll affect the color of the new soap base. Too much and it could lean towards gray in shade.
An elegant way to make partial rebatch soap is a technique that results in a granite-like effect. I learned it from soapmaker Sveta Dayan and to best achieve it, choose two or three colors of soap shavings. Use the ratio of 25% mix of shavings to a new soap base. Then stir them into a new batch of soap of any color — light to dark — to create a granite effect. Using light to medium colored shavings in a charcoal soap recipe looks like dark granite. Use a mix of light, medium, and dark tones in a light soap base, and the bars will look like lighter-colored granite. I especially love it in the pink base that is just below. Sveta achieved the pink colors by using zinc oxide throughout each batch. The colored layers use paprika-infused olive oil and turmeric-infused olive oil. Beautiful! Thanks for sharing your images with us, Sveta True Soap :)
Coloring Partial Rebatch Soap
The color effects so far tend to result in bars with speckles. Even mixing soap shavings of the same color as the new recipe will leave subtle speckles. But what if you want to recolor your rebatch soap?
So far, I’ve explained that the color of the shavings can affect the color of the new soap base if they’re dark enough. So dark blue shavings can turn the new soap a light blue. However, you can add a soap colorant to the rebatched soap, and it will color the part of the batch that’s new soap. It’s a little tricky to color the shavings, but it is possible.
There’s a point when you stick blend the soap shavings into warmed oil in the instructions. If you do this step well before making soap, you can keep the soap shavings and oil warm over an extended period. The warmth, and regular stick blending of the shavings, make the pieces very small. With perseverance, small enough that you can’t see them in your end bars. It also softens those pieces helping them almost dissolve. When they get to that stage, they too can take on the new colorant you add to the batch.
Scenting Partial Rebatch Soap
If you’re making a partial rebatch soap batch with unscented soap shavings, adding fragrances is simple. Simply calculate how much essential oil to add to soap for the new soap in the batch and the soap shavings.
Let’s use the below soap recipe, for example. If your partial rebatch recipe includes 575 g (20.28 oz) new soaping oils plus 225 g (7.94 oz) unscented soap shavings, you’ll have a new 800 g (28.22 oz) loaf of soap. Lavender essential oil typically has a 3% usage rate (depending on the manufacturer). Three percent of 800 g would be 24 g (0.85 oz) of lavender essential oil for the batch.
One of the main reasons for rebatching soap is that it’s a batch you’re not happy with. It could be a new batch that didn’t turn out as you’d planned regarding design or color. It could also be a batch that’s lost its scent. If you used essential oil or fragrance to make the old soap, it will also be in the shavings and make its way into the rebatched soap. That pertains to soap that’s lost its scent, too. Even though you can’t smell much, the restricted allergens from the EOs/FOs are still there. So refer back to your fragrance notes on the old soap batch(es) and/or calculate fragrance for the new part of the soap only.
Using Failed Soap Batches
Our old and ugly soap stashes are the best material to start with for the partial rebatch method. Fully cured soap that is still good — meaning that it doesn’t have Dreaded Orange Spot (DOS) or any signs of rancidity. I’m very sorry, but if it does, there’s no saving it. If not, grate away and remake those old bars into new ones!
You could have made a big boo-boo in making a batch of soap and are wondering if you can fix it. Maybe the soap is too soft, or you forgot to add an oil, and the bars are lye heavy. Yes, you can use this method to fix them with some caveats. Softer soap bars create shavings that melt down a bit easier than harder/cured soap. To make a better batch of soap, though, mix the shavings into a new recipe that’s on the hard side. So a decent amount of oils like coconut oil, shea butter, or cocoa butter.
Lye heavy soap comes from making soap with too much lye. It can have a pretty high pH that would be uncomfortable on your skin but fine as a solid dish soap recipe. You can rebatch it into gentler soap, though, too, providing that it doesn’t have air bubbles that could contain granules of lye. First, you should work out just how lye-heavy it is by referring to your notes on omitted oils and testing the pH. That way, you can better compensate for the difference when increasing the superfat in the new recipe. If the soap has any suspicious leaking or features, I don’t recommend attempting to rebatch it.
How to Rebatch Soap Using the Partial Rebatch Method
- Stainless steel pan
- A bowl for measuring the liquid oils into
- Cheese grater or food processor
- 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)
Choosing a New Cold Process Soap Recipe
- 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.
More Soap Inspiration for you to Try!
- 7 Ways to Make Handmade Soap (easiest method to most advanced)
- Simple Soap Recipe from Start to Finish
- How to Make Salt Water Soap
- How to Make Coconut Oil Soap