Rebatching Methods For Hot or Cold Process Soap

Wise soapmakers have learnt that handmade soap is never wasted, That is what rebatching and hand-milling is for, even your worst soap experiments can be reclaimed with some heat and patience.

What’s the difference between hand-milling and rebatching you ask?

To be honest not much. Hand-milling is usually done by soapmakers who don't want to use active lye, or who want to use a fragrance oil or essential oils that won't stand up to the heat created from the saponification reaction.

Rebatching is used by soapmakers to reclaim or recycle and reuse their Cold process or hot process soap scraps, off cuts, failed soap batches and soaps that are no longer suitable as is.

Rebatching Methods

Your Cold or Hot process soap has turned out too caustic from following a recipe with the wrong saponification values or you forgot to add the superfatting oil or forgot an oil altogether. Don't panic, this soap can be rebatched. The sooner you get rebatching your fail soaps, the smoother and easier it will be to remold them, if you can’t rebatch right away keep your soap in an air tight container until you can.

Too caustic

Please use the step by step instructions for Hand-milling natural soap bases for this rebatch method

If the soap base that you are rebatching is too caustic, you can add the missing oils either at the beginning or at the end of cooking, or half and half depending on the amount of oil that was missing.

Too much oil

If the soap you are rebatching has too much oil and not enough lye, you can add this soap shredded or grated to a new batch of appropriately underfatted fresh soap base, which you will then cook following one of the Hot Process methods (instructions coming soon).

To calculate the amount of lye to use in this batch of fresh soap, you will need to add up all the fats/oils in both batches of soap (the new batch and the failed batch). Then subtract from the total amount of lye needed for your superfatted ratio chosen in you new batch of soap, your amount of lye used in the failed batch.

New batch fats oils + Old batch fats oils = total fats and oils used in batch of soap
Total lye needed for the amount of oils for superfatting ratio – lye used in old batch = lye needed to be added in new batch.

Remember however that rebatching soap that has turned out too caustic can only be done in relatively small errors. If you have left out more than 20% of the total oils/fats or have accidentally doubled the amount of lye needed you can’t rebatch but you can still use it. Please read on.

Really Caustic Soaps

Soaps that have more caustic soda than the rebatching can mend should never be used on the skin but can still be used. These soaps make wonderful laundry soap, you can recycle your caustic soap into laundry soap in one of two methods and they are both quite simple.

  1. Simply grate or shred your soap and use as is or
  2. Dilute the soap with water and create a laundry gel (instructions coming soon)

Your soap scraps and rejects

your soap scraps and off cuts, as well as any other soap that is no longer usable as is, maybe the scent is no longer there or you just don’t like the recipe or color anymore can be rebatched according to the hand-milling for natural soap bases.

Rebatching soaps of different colors together can give very visually appealing effects to your new soaps; your colored soap scraps can also be added to your fresh batches of cold process and hot process soaps and make confetti bars.

Your DOS soaps (your soaps that are going rancid) and soaps that have developed mould can also be rebatched into laundry gel, after you have scraped off and cut out the mould and dark spots, and adjusted the amount of lye according to the recipe for laundry gel (instructions coming soon).

Soap from your pots and tools

The soap that is stuck on your pots and tools should always be reused rather than washed away. The best strategy is to let the soap set overnight then add some water to the pot and simmer for a few minutes. Your spoons, paint stirrers and utensils are then washed in this pot of hot soapy water, which can then be used in making laundry gel. If the soap was superfatted to more than 2% and you are planning on using it for laundry gel than you will need to dilute a little bit of extra lye in the water before boiling.