Many times I get asked in classes, “What is the difference between Hot Process Soapmaking and Cold Process Soapmaking?” Here is the answer:
Hot processing is a technique where a soap base is cooked at low temperatures between 180 – 200°F for 2-3 hours. During this process fatty acids are neutralized and produces clear liquid soaps and transparent bar soap.
Cold processing involves no cooking of the soap base. Yes, the oils are heated and combined with the lye solution, but this does not constitute a hot process. The oil and lye are combined between 80-110ºF and then poured into molds. It is during this time that the cooking method takes place and the soap basically, cooks itself. This photo below represent the gel phase.
It also during this time that many soapmakers (including your truly) will incubate their soap with a towel to increase the chances of getting their soap to the gel stage.
My specialty has always been Cold Process Soapmaking, but I am about to change that. The process between the two methods is very similar and requires similar equipment. I plan to come out on the other end of this weekend with my first batch of Hot Process Soap in the form of liquid soap.