Rebatching, also known as milling, is a process by which existing soap can be shredded, melted down, and turned into fun new soaps. There are several applications for this technique. One is for soapmakers to salvage a batch that’s not gone quite right; it affords the opportunity to tweak proportions of things a little and try to bring a soap back into the fold when it’s gone a bit wrong. Another is the ability to incorporate scents or embedded items which are too delicate to withstand the harsh alkaline environment of raw soap.
Perhaps the best advantage of rebatching, though, is that it allows a remarkable degree of customization, and affords those who would prefer not to work with lye the ability to exercise their creativity in the realm of soap. Rebatching is fun, easy, quick, and at its simplest requires no tools or ingredients not found in the average kitchen, with the exception of the soap itself.
Any bar soap can technically be reworked and reformed in this fashion, but handmade cold- or hot-process soap works best, and the younger (less-cured) the better. Once you have obtained the soap you wish to use, you’ll want to shred it (or buy our pre-shredded rebatching base) to reduce the amount of time it will take to melt, and also help ensure even melting. For the sorts of quantities we’re dealing with here, this can be done quickly and easily with a regular box grater.
How much soap you start with depends on how much you want to make! This tutorial is structured around the idea of making a single bar, so it starts with about four ounces of soap, which is then placed in a quart size freezer bag (freezer bags are best for this method because they’re made of sturdier plastic than regular storage bags, and it’s going to get hot later).
Add a tablespoon or so of water or other liquid. This is one area in which you can be creative – use milk, chamomile tea, beer, whatever you like! The amount of liquid needed will vary based on how cured (dry) the soap you start with is, so you may need to tinker with it a bit. Err on the side of less liquid rather than more, though; you can always add more later and then repeat the next few steps, but once you’ve added too much your only options are adding more shredded soap to the mix or ending up having to wait for WEEKS for your soap to be ready to use when you’re done. If you’d wanted to wait that long you could have made soap from scratch instead!
Press out as much air as you can from the top of the bag, seal it, and gently work the soap inside the bag such that the liquid you added is distributed over all the soap. Don’t get too vigorous about it, though; any suds you work up in the soap in there now will almost certainly still be in your finished soap and make it feel spongy. (Note: Creating this effect on purpose is one way to end up with Floating Soap!)
Now it’s time to bring on the heat! There are multiple schools of thought on this, but over time I’ve come around to the oven method. I simply set the oven on “warm”, place the bag o’ soap on a pan or dish to keep it from direct contact with the oven rack (if your oven runs hot, you can fill the dish half-full with water before adding the bag of soap as an extra protection against melting the plastic), and into the oven it goes, for . . . well, for as long as it takes. Sometimes it takes a couple of hours…
…but this time, not so much. Back into the oven for another hour!
This soap was a bit drier/older than is really ideal for rebatching with, so it took a bit longer than it might have otherwise, but one thing is just as true about rebatching as it is about all other things in soaping: You can’t rush it! It’ll be ready for the next step when it’s ready, and not before. So keep checking your soap, and when it’s all translucent and sort of gloopy (about the consistency of oatmeal), then it’s ready to go. If it is persistently failing to reach that point, you may need to add a bit more liquid. Don’t be afraid to experiment a little. After all, it’s just soap, and there’s not much you can do that will ruin it completely. Be careful, though, it’s hot!
Right. Now that the soap is all gloopy and gloppy, it’s ready for the next step. (If you don’t want to add fragrance and/or color, you can skip either or both of the next two steps and go straight to the into-the-mold stage.)
It’s time to add the smell-good stuff! Any skin-safe fragrance can be used here (don’t use potpourri fragrances, diffuser oils, or most candle fragrances). Most people don’t have a soap supply store in their hometown (not that I do, either, more’s the pity), so the easiest place to find scents you can use for this may be the essential oils counter at a health food store. Some of these are very expensive, but if you look a bit, you shouldn’t need to break the bank to be able to find something you’d be willing to smell like after a shower.
I add fragrance in small amounts with a pipette, visible in the photo above. Most people don’t have those, so I’ll translate to other terms. My default fragrance percentage for soap is about 1%, which means this 4 oz batch got about 0.05 oz of scent. If you have a sensitive kitchen scale and a delicate hand with the pouring, you can stop there and use that measurement, but if you’d rather not risk a momentary hand-twitch upending the entire bottle of fragrance into your hapless soap batch, we can translate it into volumes, and you can use a quarter-teaspoon. It’s an approximation, but for these purposes it will do. This amount is only a starting recommendation, of course – this is your soap, it should smell like you want. Use more, use less, use however much you like! Once you have added the scent, close the bag back up tight. Either wearing heat-proof gloves or after wrapping the bag in a towel, squeeze and squish the bag until the fragrance is thoroughly mixed in to the soap. If it cools off and starts to set up around the edges, toss it back into the oven for a bit to re-melt.
I also added some color to this batch, in the form of LabColors, which are a bit on the pricy side for tinkering/hobby purposes. You can use food coloring if you like; just experiment and see what sort of results you get. Or, when you go to the health food store to get the essential oils, take a look in their bulk section and see if they have any dried flowers or other fun things you might want to mix into or sprinkle onto your soap for some visual appeal. Lavender buds, calendula petals, lemongrass – there are all sorts of possibilities! If you’re mixing in color, you can do it at the same time as you’re mixing the fragrance, but I like to do it separately afterward – it’s hard to see the fragrance to be sure it’s all mixed in, and if you think it’s all mixed in, then add color and mix that until you can see it definitely is all mixed in, then you can be pretty confident in assuming the fragrance is completely and totally mixed by that point. If you’re using flowers as mix-ins, add them at this point, too. And don’t forget the gloves/towel, because the soap is still hot!
OK, once you’ve got everything all mixed in, it’s time to put it in the mold. What’s that? You don’t have a mold? Well, neither did I the first dozen or so times I did this. I’ve used washed-out yogurt cups, muffin tins (with liners), ramekins, and just about anything else I could find in the kitchen that was more or less the right size. If you happen to have one of those silicone individual-brownie pans, those are just about perfect. Things that are flexible are best, because it’s easier to get the soap out of them afterward – and if you do happen to want to use a meant-for-soap mold, try to pick one without large amounts of detail. Rebatched soap is not liquid when it goes into the mold, like melt-and-pour or original cold process, so it doesn’t take up detail well, and indeed can get hung up on the little finicky bits of the mold and tear when you try to take it back out.
This being just a single-bar batch, you can get it out of the bag the easy way: Cut off a corner of the bag and squish it out into the mold you’ve chosen, then lay the bag down over the surface of the mold and use it to help you smooth the top of the soap flattish – but take it back off pretty quickly, before the soap tries to set onto it. If you’re adding flowers/etc. to the top, add them now and press them in gently so they will bind to the soap.
See how it doesn’t fill the mold quite to the corners, even though it’s a simple square? I could have squished it a bit more tightly into the mold, but I’ve learned to embrace the rustic and organically-shaped nature of rebatch – and, in fact, I let this one keep some unmelted bits of soap specifically because I wanted the speckled look they produce in a colored milled soap.
And voila, a bar of soap. It was ready to unmold the day after I made it, which is not necessarily usual; sometimes they need a few days if you use more liquid or the soap was newer or any number of other variables. But it’s pretty much ready to use as soon as you finish it, though if you leave it to dry a while longer it will probably last better once you start using it, and if it still feels soft to the touch it definitely should stay on a shelf a while.
And there you have it! Rebatching is fun and easy, and if you find you like it, you might just end up giving everyone you know gifts that you made yourself!
Many people prefer to put the freezer bag into a pot of boiling water rather than into the oven. This has the advantage of being a constant and known temperature, whereas the oven can fluctuate, but I’m not fond of steaming up the kitchen and having to keep topping up the boiling pot. It does certainly work, though, if you’d rather do things this way.
If you get the rebatching bug in earnest and want to make batches larger than can readily be done in even a series of freezer bags, there are several methods for doing that as well. Melting the soap in a double boiler, in a crockpot on low or warm, or in a bowl in the oven at low temperatures are the main contenders. Try them all and see what works for you!