Involves partial hydrolysis of the glycerides to mono- and diglycerides while glycerol and free fatty acids are also liberated. The hydrolysis is hastened by the presence of moisture, warmth, and lipases present in fats. As a result of the liberation of volatile butyric acid, hydrolytic rancidity produces a disagreeable odour and taste in fats that contain a high amount of volatile fatty acids, for example, butter. Butter undergoes rancidification more easily in summer.