We have run into questions on different soap making processes a few times so I thought it would be nice to put a post together about the differences.Cold process soap is soap made without adding much additional heat in order to reach saponification. Once the soap goes through saponification and cools off (24-48 hours) it is ready to be cut and then cure for anywhere from 3-6 weeks depending on the recipe and climate in which it is curing. Before I get ahead of myself saponification is the chemical reaction in which oils (acids) and sodium hydroxide or lye (the base) mix together into an emulsion to become soap. The soap making process creates its own heat in an exothermic chemical reaction. It's really neat to put a fresh batch of soap into a mold and check on it a little later, sometimes it gets REALLY hot and sometimes not so much, again it all depends on the recipe and other variables. I really enjoy watching a creation incubate into the final product.
Milled, French milled or hand-milled soap is something different. We have all most likely seen milled soap before, it is generally a very shiny hard bar. Milled soaps are not the same as a basic cold process soap. The maker takes fresh cold process soap and the natural glycerine is removed from it and it is processed through a large machine in which rollers flatten the soap into paper thin pieces. Next it is shredded and put through the rollers multiple times so that all the shredded pieces are ground back together. This mixture finally goes through an extruding machine which finally spits out a bar of compacted soap flakes. If you are looking for a natural product, this is not for you. Milled soaps are made primarily with beef tallow as many commercial soaps are as well as added synthetic ingredients which helps to give it the pretty shiny appearance. The synthetics also give it flexibility so that it can survive the rolling machines. The glycerine, which is a natural by product of soap making, is removed because it would gum up the equipment too much. On it's best day hand milled "soap" is nothing more than a laboratory imitation of the real and good thing.
Rebatched soap it sort of a marriage between cold process soap and milled soap. Rebatched soap is made when a soap maker takes a cold processed soap and shreds it up. There are no rollers or glycerine removal involved in this process. The soap is simply shredded, re-melted and remolded. There are various reasons why a soap maker would re batch a soap, sometimes the fragrance that they wanted to use is too fragile to with stand the soap making process or they want to use an expensive oil whose benefits would not be able to withstand saponification so they make their recipe then shred it down to add the extras.
So there you have it, three slight variations on the bar soap making process. Here at Soapsmiths we make cold process soaps from high quality oils, butters, essential & fragrance oils and other great skin loving additives, it's our favorite way to make a good quality product.
Toodles for now
~ Your Soapsmith
Resources: The Natural Soap Book, making herbal and vegetable soaps by: Susan Miller Cavitch