The Pros, Cons & Method For Rebatching Soap

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Rebatching soap, also known as hand-milling soap, is basically the procedure of melting down premade cold process soap. Rebatching is one of those procedures you will love or hate, so let’s take a look at the good points first.

rebatching homemade soap

Positives of Rebatching Soap

  • This process will allow you to add in any extra delicate additives such as herbs, essential oils and other various ingredients that could easily be ruined by alkalinity in the cold soap process.
  • You can also save botched batches that you would normally have to be thrown out. Simply re-melt and add any oils or ingredients you may have forgotten, or just miss-weighed or miss-calculated (have you ever had that sinking feeling when you’ve just realised you’ve forgotten to add in a particular colouring or additive, after you’ve poured them into molds? and it’s all too late, well guess what, You’re not alone!)
  • Rebatching soap also allows you to take one large batch of plain, uncolored or perfumed soap and divide it into an assortment of individual recipes.

Negatives in Rebatching Soap

  • Rebatching soap is quite a lengthy process (it could take 2 to 3 hours just to melt the soap).
  • Rebatched soap doesn’t always have the nice smooth look and feel of freshly made cold process or melt and pour soap. And often has to be trimmed and shaped once its hardened.

Rebatching Process

So having noted the pros and cons of rebatching soap lets get to the process.

For best results, try rebatching soap when it’s still fresh (about 2 to 10 days would be considered fresh). The fresher the soap the more water it will still contain making it much easier to work with.

If your soap is older than 10 days don’t worry, you can still rebatch it but you will need to replace the moisture the soap will have lost. For a vegetable based soap its best to add milk to it when melting, I’ve used cows, goats and buttermilk and all have worked well. For a tallow base soap use distilled water.

What you will need

  • Cold process soap
  • Liquid (distilled water or cold milk) approximately 9 oz per lb of soap; if your soap is very fresh then you’ll need less or even none
  • Large hole grater
  • Double boiler, an electric oven, or a crockpot

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  1. Start by shredding or grating the soap as finely as possible then place it in to a crock pot, ovenproof bowl, or the top half of a double boiler. Add the appropriate amount of liquid remembering to use milk for the vegetable based soap and distilled for the tallow based soap. Give it a good stir until all your soap is completely coated in the liquid, and then leave it to sit and absorb some of the liquid for 2 or 3 hours before melting.
    rebatching soap
  2. Don’t forget that if your soap is still nice and fresh, you shouldn’t need to use any liquids, but if your soap is looking rather dry it’s a good idea to add a little, this will create a layer which will stop the bottom from burning.
  3. If you are using a crock pot turn it on to the lowest setting. Your oven will need to be set at 145F to 150F and the double boiler needs to be kept at a steady boil.
  4. Stir the soap well and then cover it, if your ovenproof bowl doesn’t have a lid cover it with foil. If you are using a double boiler, keep your eye on it giving it a quick check every 10 minutes or so. If you’re using a crock pot or an electric oven, then you will only have to check on it every half an hour or so. Try not to stir the mix whilst it’s melting, just give the sides a scrape down each time you check on it.
    melting soap for rebatching
  5. After 2 to 3 checks, if your soap is still looking fairly solid, and a little dry, add some extra liquid and give it a gentle stir. As the soap becomes smooth (this stage will take a while, up to an hour or more, so try to be patient) don’t add any more liquid at this point but if you are using the double boiler method, keep your eye on it to insure that the bottom is not burning. If you do see your soap starting to burn, then to reduce the temperature by adding a little cold water to the bottom of the boiler to cool it down.
  6. After a while (anywhere between 1 to 2 hours), the soap mix will get to a point where it isn’t going to get any smoother, and it’s consistency will no longer change. This is a good time to add any additives to your soap. Stir in the additives and continue heating and thoroughly stiring every now and then to insure it doesn’t burn. The soap doesn’t always melt to a total liquid so if the texture doesn’t change for a long time, then it’s not going to. Remove the soap from the heat and let it cool for a little while.
  7. Prepare a mold by rubbing it with a little petroleum jelly (I personally prefer to use those flexi silicone muffin trays, mainly because you can easily pop the finished soap out of them without needing to grease them.)
  8. Once the soap has cooled enough, transfer it to a mold by pouring, spooning or pushing depending on how thick the soap mix is. Alternatively you could whip the soap up using an egg beater to produce floating soaps, before carefully spooning into the mold.
  9. Leave the soap to harden (about 24 hours) then remove it from the mold. Trim or shape the soap if needed and allow to dry out (cure) for 3 weeks to make the soap nice and mild before using.

Have you rebatched soap before? What tips can you share with me?

Discussion (23 Comments)

  1. Hello Angela,
    I made my soap about two weeks ago but every time I try to test it I discover it doesn’t foam. What am I going to do now. I used the lye calculator to get the right amount of lye and water.

    • This is very unusual. It doesn’t lather at all? Sometimes, if you have hard water, soap doesn’t lather very well at all. If you have some spring water in a bottle hanging around, try testing with that instead.

  2. I made a batch of hp soap and didn’t calculate my lye solution right. My soap came out super soft. Can I rebatch it or should I just toss it?

    • Hi Kirsten,

      You could try to rebatch it but you might struggle with how much lye to use. So I would say it is probably easier to start again. You can still use the soft soap though so no need to throw that batch away. Perhaps leave it to cure a few weeks longer and it might continue to harden.

  3. I made a batch of melt and pour olive oil soap with dried herbs. I did not use enough of the soap and now it looks like a bar of herbs. I wanted a floaty herbal olive oil soap. Can I rebatch and add more olive oil soap? Or should I try something else – like throw it away. Any suggestions?

    • Hi Wanda,

      If you’re not too worried about throwing it away, I absolutely would try to melt it down and add more soap. Although keep in mind that this can ruin the lovely scent you’ve added to your soap, so you may with to add more.

      • Thank you Angela. I will give it a go. Got nothing to lose at this point, except more soap LOL

  4. Hi Angela,

    Can you rebatch old soap? We made our soap a year ago (well the daughter did!) and we have forgotten about it. It is a plain soap, no fragrances and I’m pretty sure tallow based but would have to check with said daughter. Do you think it would be fine to do as we would like to add fragrance or is it best do use as is?
    Thanks Christine

    • I like to stick to rebatching just the once. While technically you can rebatch as many times as you like, and it will still be soap, the more you do it the more complicated it gets. Just stick to the one or two times if you ask me.

      Hope this helps!

  5. My soap bars going to coverd with white layer as it is drying with time please tell me what can I do

    • Hi Dinesh!

      Yes, you’ve encountered a problem that can plague many a soapmaker! So don’t worry, it’s not just you. The problem you’ve found is called ‘soda ash’ in the industry. This is a thin layer/film of sodium carbonate on the surface of your soap. While this is completely harmless, it can look rather unsightly.

      There are a few ways you can try to prevent this build up. The first is making sure your soap is well protected during the saponification stage. Ensure you’re popping your soap mixture somewhere warm while it hardens in the mold. Wrap it with an old towel (make sure not to use the towel for anything else going forward) and pop it in a warm cupboard. You could also try placing the mold in a large, air tight, sealed tupperware (again, do not use the tupperware for any other purpose once you’ve used it for soapmaking) so that the air cannot get to it.

      If you’re still having problems, take a look at the temperatures of your lye and oils when you come to mix them and ensure they are properly balanced and within the guide lines I’ve stated. I would also make sure your soap has reached a good trace before you pour into your molds as I’ve found a very thin trace can build soda ash more readily.

      I hope this helps!

  6. Hey
    I did my coconut Shea bar(cold process) but the soap is still soft and it has been a week plus. I think the lye is less and I want to rebatch it. Is it OK to add lye to it when rebatching?

    • Hi Johnette,

      The short answer is yes, it totally is possible to add the extra lye that was left out during the first process. However, it’s kind of important to know how much lye you’ll need. Do you have a rough idea of how much extra oil/butter/FO/EO went into the recipe? If you don’t know what the mistake actually was, you run the risk of adding too much lye and ending up with very caustic bars. So I would say be cautious, adding a bit at a time unless you’ve got a pretty good idea of what went wrong.

      Good luck!

  7. Hi there,
    I am rebatching coconut oil soap I made about 9 weeks ago but am not happy with the shape. How long should I cure it for after I rebatch? Or is it okay to use as soon as it hardens?

    • Hi Ella!

      Sorry to hear you didn’t like the shape of your coconut oil soap. When you come to rebatch it, you shouldn’t have to cure it as such. Like you say, just wait until it hardens. Hopefully you’ll like the shape better this time!

  8. can I add layers of cold process soap to existing batch of cold process soap 3 days later? Trying to make a pie soap and need a few more layers to my existing batch. will the layers seperate or am I ok to add a few days later?

  9. Hello Angela,

    I made a soap where I missed an oil and thus ended up with a 42% castor oil soap 🙁 The soap looks great and good until I use it! Then, as expected, it gets very sticky and “wetty”. What can I do with it?
    Re-batching would be a good idea, or I’ll end up with the same sticky mass?

    • Hi Anamaria
      First, if you are not happy with the results of any soap make sure you always test it using a ph strip before using, make sure it is somewhere between 7-10. It’s difficult for me to say 100% without knowing what recipe you followed, but generally you can rebatch soap and add the solid oil that you forgot. If the soap is not usable as it is, you have nothing to loose 😉

  10. Hey I did my first attempt at soap on Sunday and it’s now Thursday and the soap has not hardened as of yet? Should I re batch it and add more lye?

    • Hi Mae

      The last soap I made took a week and half to harden and still wasn’t completely solid. I then removed it from the mold and that helped it solidify more.

      I’m not sure what soap you have made but some are softer than others and as long as you measured your ingredients and followed the cold process it should work, my guess is it just needs more time 😉

      • Plus, If its too soft to get out of the mold I sometimes put it in the freezer for a while.

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