The reaction used for preparation of soap from fat is :

The reaction used for preparation of soap from fat is not alkaline hydrolysis, but rather saponification. In saponification, a triglyceride (fat or oil) is reacted with a strong base, such as sodium hydroxide (or potassium hydroxide, in the presence of heat to produce soap molecules and glycerol as a byproduct. The reaction involves the hydrolysis of the ester bond in the triglyceride by the base to form carboxylate ions (the soap molecules) and glycerol.