What Is Cold-Process Soap? Why It Is Called Natural Soap and How It Is Made

Cold-process soap is a traditional soap-making method in which no high heat is applied and the soap is slowly cured over time, allowing it to retain the essential properties of a cleansing agent as faithfully as possible. This method is a time-honored process that has been passed down for generations, and its significance lies in improving quality by leaving the process to time rather than artificially altering the characteristics of the raw materials.

The manufacturing process is relatively simple. Oils or fats are mixed with an alkaline solution in predetermined proportions and thoroughly stirred. Fragrance or additional ingredients are kept to a minimum, after which the mixture is poured into molds and allowed to harden. The soap is then left to cure naturally for several weeks to several months until it is complete. During this curing period, any remaining free alkali completes the saponification reaction and either disappears or dissipates into the air.

Free alkali refers to alkaline substances that remain unreacted after failing to fully participate in the saponification process during soap making. Commercial soaps are required to be tested to ensure that free alkali is absent or remains below regulated limits. However, in handmade soaps, free alkali may remain if the curing period is insufficient. Such free alkali can cause skin irritation and dryness.

The recipes used for cold-process soap are formulations that have been repeated and refined over long periods of time and are therefore well validated. Because this method does not rely on complex processes or new chemical ingredients, it offers a high level of stability and a low likelihood of unnecessary irritation. Made from simple materials—oils or fats derived from natural sources and alkali—cold-process soap is therefore also referred to as natural soap.