rebatching

What is rebatching?

Rebatching soap is a way to make a new batch of soap out of existing soap: gently heat the scraps in water until the mixture is homogeneous, make the desired corrections, and let the new mixture cool.

Why do it?

1. To fix soap that sucks

Common reasons:

• Unreacted lye, i.e. way not enough fat (per the “zap test,” because apparently saponification is a science you should sometimes lick)
• Not moisturizing enough; i.e. only a bit not enough fat
• Shape sucks so much you’d rather have a sliced-loaf shape instead of whatever it was before
• Texture sucks so much that you’ll accept the rough-ish texture of hot process over what you had before
• Colour sucks so much you’ll take your chances on whatever comes out of the mixture you’re cooking up
• Fragrance sucks so much you need to dilute it or try some mad science

2. To use ingredients that react poorly with lye

Some colours are pH sensitive, like the purple I tried to make by combining crimson and indigo generic liquid soap colours. In the initial batch, it turned out a gross grey-maroon colour (like hex code 9C6E77). But as the soap cured, it turned a saturated purple closer to 8432C9. I’ve used those colours before on their own and never gotten that kind of result, so I have no idea what happened, but it was pretty cool.

I expect botanicals (e.g. petals, buds, natural colourants) will also degrade in lye, which is why recipes will tell you to add those at trace when using cold process. But during rebatching is probably the safest time to do so.

I’ve read that some fragrances are prone to degrading or turning the batch an unexpected colour when they react with free lye, but haven’t yet run into that myself.

3. To recycle odds and ends

I expect soapmakers who do this as a business would have bits and bobs that aren’t the right shape or size to sell in a standardized way, and rebatching would make a mega-soap batch that’s relatively uniform. Since I’m just a hobbyist, this isn’t really my concern.

Equipment

1. A cooking vessel; one of:
   • A slow cooker or multicooker;
   • A double boiler; OR
   • A non-reactive, oven-safe baking dish
2. Soap that didn’t make the cut
3. Moulds
4. (Optional) Additives (fragrance, colourants, mix-ins)

Procedure

1. Grate or finely chop the soap into the cooking vessel
2. Add enough water to just wet the scraps
   • I’ve heard soapmakers say to think of it like you’re dressing a salad, in that you don’t want your lettuce swimming in liquid
3. Cover mixture and let it cook at very low heat about an hour
4. Uncover mixture and stir well; if it doesn’t look uniform, cover and let cool half an hour longer
5. When mixture is uniform, mix in any additives you want to include
6. Pack mixture into moulds and let harden
7. When mixture is hard enough to unmould, remove from moulds and slice if desired
8. Let cure on racks until dry enough to use