Rebatching. This is sometimes a dirty word. What is it and why do people do it?
Rebatching is sometimes confused with milling, or French milling. Rebatching is when a batch of soap is melted and additional items are added or a failed batch is reworked. Rebatching is done to make small, custom batches of soap from a large initial batch. The resulting bar of soap has a shorter shelf life than a properly prepared, handmade batch of soap. Rebatching is also a soap that is more likely to be cosmetically challenged (ugly).
Milling is when excess lye, fat and glycerin are removed from the soap and the resulting soap is shredded into flakes, pressed through a series of rollers and then molded. Milling makes a hard bar of soap that can last a long time. It is also not as skin friendly as a properly prepared, handmade batch of soap. Milled soaps are generally beautifully molded bars. These soaps are also more likely to be brittle.
Rebatching, when done to save a batch, is the only time MMS recommends doing this labor intensive work. Our favorite method of rebatching is the oven method. While still time consuming, the oven method is not a constant attention process.
To rebatch, using the oven method we use, shred or grate all of the soap and put it in an oven proof, lye resistant container (glass or stainless steel please!). Set the oven to 200 degrees F. Pour a bit of boiling water over the soap gratings and mash with a potato masher. I allow 1/2 hour for each pound of fat in the original batch. I mash and stir each 1/2 hour until the mixture appears fully melted and smooth in consistency. The mixture will probably be thick but it shouldn’t have major chunks. Small bits are OK to leave, but do expect color differences in the final bar of soap if you leave any small bits unmelted.
Add boiling water anytime you get a mixture that is too thick or dry. Do not add a lot of boiling water, just a little. If too much boiling water is added, then the soap will expand and probably float. Very wet soap is a problem because as it dries the sides will become concave.
To avoid the work of rebatching, try making each batch correctly the first time. The idea of making a very large batch of soap, then intentionally rebatching 1 lb at a time, seems to be wasteful of life’s precious minutes. No bar of soap that has been rebatched is an improvement over a properly made batch of handmade soap. Rebatching is for prevention of ingredient loss. It is a “waste not, want not” activity.