Saponification is the scientific name for the chemical reaction that occurs when a fat (I use olive oil, coconut oil, and beef tallow) combines with an alkali (sodium hydroxide or potassium hydroxide) to produce soap and glycerine.

Fat is made up of triglyceride molecules, which are shaped like a capital E with three fatty acid molecules attached to a fat; the lye breaks down into sodium ions and hydroxide ions. The sodium attaches to the glycerol backbone to form glycerine.