Hydrolysis, chemical decomposition of a substance by water. The hydrogen and oxygen atoms of water combine with the atoms or groups of atoms of the hydrolyzed substance to form new compounds. Hydrolysis is speeded by heat and pressure or by mixing an acid or base with the water. Hydrolysis is important in the manufacture of many substances. Corn syrup is produced by acid hydrolysis of corn starch. Soap is made by alkaline hydrolysis of fats. Other substances made by hydrolysis are fatty acids, alcohols, and glucose.