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!
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.
- 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
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.
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
- 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.