It is one of the processes of making soap. In the cold process of soap making no external heat source is required to bring out saponification. In this process a Lye solution (potassium hydroxide or sodium hydroxide) and water is well mixed with the proper proportion of melted fats or oils to initiate saponification process. Then the mixture is allowed to cool up till 80-90 degrees Fahrenheit. The Lye solution is poured in the oils and stirred with stick blenders. The stirred solutions turn cloudy and slowly thicken to thin pudding. Just as the mixture starts to solidify, essential oils, fragrance oils, herbs, oatmeal or other additives are added.
Further the soap is put in wooden molds wizened with heavy wax paper and covered with blankets or towels. The Saponification process is further continued for 18-24 hours. During this ongoing process the soap goes through gel phase. Once the insulation period is over the soap is solid, removed from the molds and cut into bars. Now the saponification process is complete and the soap is ready to use.
Successful cold process soap making involves exact amount of Lye solution and the correct saponification values of the oils used for soap making. If the Lye solution is more than the required proportion the unreacted lye will result in burning and irritation of the skin due to very high PH.