Saponification
The reaction that turns a fat and a strong base into soap and glycerol.
Saponification is a chemical reaction that turns a fat (triglyceride) and a strong base (lye or potash) into a fatty-acid salt — soap — and glycerol. It is one of the oldest chemical reactions mastered by humans, attested as early as 2500 BCE on Sumerian tablets at Girsu.