Rebatching Cold Process Soap

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With rebatch, you can reuse remnants of unused cold process soap. And as long as you can get a batch of cold process soap, it’s also a no-lye soap making process!

Rebatching

There is no soap maker in this world that never made errors at making a batch of soap. We all make experiences and we all make some errors at some point. Especially with handmade soaps, where there are a lot of variables we don’t control: ingredients quality and even sometimes composition; ingredients measurements (kitchen scales are not very reliable…); lack of precise instructions; human error.

As long as your soap is not lye heavy – there’s no remedy for that, and in that case, the soap should be discarded -, you can use your failed or old/unused soap batches and literally reshape it. Rebatching is very simple in theory, but requires the knowledge to recognize when the soap mixture is ready (just like “trace” in cold process).

Besides recycling soap, another advantage of rebatching is that this is a no-lye soapmaking process. Your soap is made and lye has already been dealt with. So, with this process, you can use delicate scents, herbs or colorants that otherwise get altered or even completely eliminated with saponification.

To Rebatch or Not To Rebatch

If you read about rebatch on the internet you will probably read about people that defend the rebatching process and people that avoid it at all costs. You can, for example, read a discussion about the theme in Soap Making Forum. I will then explain how the process works, what are their pros and cons so that you understand why there is some debate.

Rebatching process:

  • Grate soap
  • Add water or a liquid (like milk)
  • Heat the soap along with the liquid in low, constant heat while mixing
  • Add fragrances and colors (optional)
  • Pour into molds
  • Unmold/cut and let the soap dry

Pros

As mentioned, rebatching is a great way to reuse soap batches that went wrong (even soap that didn’t saponify completely, although that never happened to me). 

It is also the only way to use some special, delicate scents or herbs inside your soap that wouldn’t survive otherwise (with saponification).

You can personalize soap with herbs, colorants, scents and shapes. You don’t need to use lye as the soap is already made. 

Might not be seen as a pro, but I do like the rustic looks of the resulting soap.

Cons

 Grating soap, especially a high amount, is a pain for your arms – literally. You can use a food processor for that, but then you do need to clean it up…

Rebatched soap looks pretty much like hot process soap: it has a rustic texture, where you can see some “grainy” forms. While I do like that rustic looks, you really can’t reach a uniform and smooth look, only possible with cold process.

There’s nothing like cold process or hot process fresh soap. Some people use this fresh soap to make a rebatch and add more delicate scents. Delicate scents are usually expensive ones. Why would you use expensive essential oils in soap that will no longer be completely fresh, and will have a rough/rustic look? This is just my opinion, and as I said there is debate and both opinions are valid.  

Soap is a wash-off product, so why try to use it for something that was never conceived for: adding scent to your body? More easily, I’d use those expensive delicate fragrances in a special body lotion or cream. There’s no saponification to destroy the essential oils, and the product stays and gets absorbed by your skin.

This is more like a warning that a con about rebatching: DO NOT use commercial soap to rebatch! Commercial soaps are not made of soap salts, but surfactants, see Commercial Soap Ingredients – What are they?. They have other sort of ingredients that may get chemically altered with heat. The resulting substances might do more harm than good – rashes, irritation, or other allergic reactions. 

Rebatch can only be used for handmade soap: cold process or hot process.

Shelf life might also be a problem. In this rebatch tutorial/recipe from Soap Queen, they indicate a shelf life of 1-2 months to use the rebatch soap. Mine still looks good after 2 months and I plan to use it, but rebatch soap might not be a good idea to give or sell – again cold process or hot process soap will last for one year or more, if your ingredients have long shelf lives. 

And Finally, the Recipe!!

As a conclusion, my opinion is that rebatching is a great way to reuse cold process soap, although it doesn’t replace fresh-made soap by cold process. I’ve also liked the rustic, grainy looks. 

The recipe I’ve made was a way to use some single colorful soap bars (some with too much soda ash to look good) and two crumbly batches of castile soap, all made by cold process. My idea was to look like the soap was made of colorful glass 🙂 Most of this soap was several months old. 

I’ve also used an essential oil blend (lavender based) I didn’t like particularly, but the final soap scent was very good! 

The resulting soap was good and very pretty, although a little bit crumbly. I think it’s time to invest in a soap bag to use soap scraps 🙂 I was afraid to give this soap as a gift due to the short shelf life, but looks very good to use it for me.

 Enjoy this recipe! I hope you have as much fun as I had while doing it.

Rebatching Cold Process Soap

Sofia Matias
Rebatching is a technique to re-use cold process soap. As long as the issue with the soap is not excess of lye, you can redo any soap into a new one, adding colorants or scents that cannot survive the saponification process. This is a way to make soap without lye!
Prep Time3 hours
Cook Time30 minutes
Total Time3 hours 30 minutes
MethodRebatch
ProductSoap Bar
Servings10 soap bars
CostNo cost – Soap recycling

Ingredients
 

Instructions

  • Grate the white soap into a bowl. This might be the longest operation of this recipe.
  • Chop the colored soap into tiny cubes (1 cm approx.). Pour your grated soap and the minimum quantity of water (80 to 100ml) into the slow cooker or your pan
  • Turn on the slow cook into high heat and have some water at the ready
  • Be patient now. Let the mix warm up and mix it with a spoon every now and then. This operation might take 20 to 30 minutes until the soap starts to look like a consistent mixture. The grated soap needs to "melt" into the water.
  • Add the soap cubes around 20-25 minutes and mix some more. Let the cubes get some heat so they incorporate in the mixture as well.
  • When the mixture looks like mashed potatoes and the grated soap bits look fully incorporated it's time to add the essential oils. Mix well and now the soap is ready to be poured.
  • You need to be quick to pour the soap into the mold. As soon as the soap mixture leaves the heat, it starts to harden… Bump the soap mold hard against the countertop several times, to remove any bubbles. Be careful with spilling 🙂
  • Let the soap harden for 24 hours, then unmold and cut. Let the soap fully dry for 7 days.
Tried this recipe?Let us know how it was!

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6 thoughts on “Rebatching Cold Process Soap”

  1. This article gives helpful information about what best to do with the leftover pieces of handmade soaps. You have listed out pros and cons of the process, and that is a great resource. I liked your view about whether to use fragrances or not in these recycles soaps.

    At the same time, I feel one can get creative with shapes and colors. I don’t have any experience in rebatching soaps. So with your experience, you can answer this better.

    It would be great to have a video showing the complete process of this method of soap making.

    Reply
    • Hello Deepshikha, thanks for your comment and interest on this post.

      Handling rebatched soap is not that easy as it looks, because the soap tends to harden as soon as it cools down a bit. It’s also not a liquid, it’s more like a paste, so you need time to spoon it over silicone molds for example. It’s not impossible, but it’s for someone with some experience. I myself pour it over a loaf soap mold, it’s easier 🙂 Of course, you can always give it a try. Just remember that this rebatch process is valid only for natural, handmade soap, do not try it with commercial soap bars.

      About the video, I will make one, but I am indeed a bit delayed on making videos for many of my posts, as videos require more work than writing content 🙂 But thanks for the suggestion.

      Cheers,

      Sofia

      Reply
  2. Lovely clear post on how to re-batch cold process soap.

    I like the way you can save a faulty batch and re fragrance and re-mould it into something different.

    The instructions or recipe is clear and concise and the images are excellent.

    You have created good links to other related topics and the fact you can use regular kitchen utensils rather than needing specialist equipment is also a really positive point.

    Very interesting and educational post.

    Thank you.

    Reply
    • Hello David, and thanks a lot for such nice and encoraging comment!

      Yes, soapmaking is indeed much more accessible to all of us than we might think. 

      Rebatching is indeed a great way to turn soap scrapes, faulty soap (as long as it’s not lye heavy) or old soap into something new. Without any experience or guiding material it might be difficult to get a good result, as soap takes more or less half an hour under heat to properly blend with water. But apart from that it’s a very easy recipe.

      Remember, you can only do this safely with natural, handmade soap.

      Commercial soaps, which are actually detergents (made with surfactants), are different from handmade soap, and therefore may be chemically altered with temperature into… unknown substances, maybe some toxic, as this detergent bars are not made to be reheated. You may know the difference after reading this article.

      Come back to my website to read more about soap making and how is it made 🙂

      Cheers,

      Sofia

      Reply
  3. Thank you Sofia for an informative post. I myself have not tried soap making yet, but its been on my to-do list for years, and I’m finally considering having a go at it. Really liking the idea of rebatching (especially to fix a beginners mistakes), for I hate letting anything go to waist. I’m not real big on the idea of grating it though. Lol

    What tools/equipment do you recommend a beginner to get who is just starting out?

    Reply
    • Hello Brandy, thanks for your comment.

      To start out with soapmaking, cold process (make soap from scratch) or melt and pour (use premade soap base) are the best ways. Choose what you prefer. They have more or less the same sort of equipment, you just don’t need an immersion blender for melt and pour, and you also don’t need to deal with lye. Check my article How To Make Soap For Beginners. Rebatching is more for people who have dome soap and it went wrong 😀 And yes the grating is a pain, lol. And I DO NOT recommend to use used soap or commercial soap bars: they have a different chemical composition from natural soap, and the heating might change their composition creating potential toxic substances.

      Most of your equipment to make soap is actually in your kitchen!! I’ve bought some when I started simply because I had no pyrex at home 🙂 You can also use recycled yogurt cups or carton milk boxes, but to be honest, I personally preferred and always used silicone molds (it can be the ones for small cakes or chocolates if you have them!). Check out my article How To Make Soap From Scratch to learn it all. Then, each recipe list exactly what equipment is required.

      Cheers,

      Sofia

      Reply

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