Hand milling is a process that allows herbs and delicate fragrances to be introduced into the soap without suffering heat damage. That is a longish process which lengthens the production two fold. First we make the soap, which could take more than an hour if the hot processed method is used. Then we mold the soap, wait until the next day and unmold it. This is when the hand mill/French mill process takes place.
We chop the soap up into smallish bits. Put those bits back in the crock pot and melt them down. Why? The heat from the lye is really too strong for the essential oils, herbs and fragrances to keep their properties. It's called flashpoint; the point at which the heat, thermal or chemical, is so high it kills the those sensitive properties. The water and lye mixture reaches above 200F while citrus oils flash at 90F.
It's hard for the Lavender Essential Oil, whose flash point is 118F, to maintain its fragrance at that temperature. But with soap bits melting at 105F and being allowed to cool a bit, I have an another opportunity to increase the usefulness of my soaps by adding fragrance oils, or essential oils, or honey and other other sensitive herbal ingredients.
Then its fragranced, re-molded and unmolded, re-cut and packaged. That process gives you a harder, longer lasting, more fragrant bath bar without the chemicals.