The leachate of certain plant ash, especially from hardwoods, is used in local soap making because it contains potassium hydroxide (KOH), which is a type of lye. KOH is an alkaline substance that reacts with fats to produce soap through a process called saponification. While sodium hydroxide (NaOH) is also used in soap making, KOH-based soaps are known to be softer and are often used in liquid soap formulations.