Saponification's the hydrolysis of an ester under basic conditions to form an alcohol and the salt of a carboxylic acid (carboxylates). Saponification's commonly used to refer to the reaction of a metallic alkali (base) with a fat or oil to form soap. Saponifiable substances are those that can be converted into soap. Sodium hydroxide (NaOH)'s a caustic base. If NaOH's used a hard soap's formed, whereas when potassium hydroxide (KOH)'s used, a soft soap's formed. Vegetable oils and animal fats a… (More on Saponification)