The choice of a lipase for an esterification reaction can be determined from the esterification reaction between butyric acid (0.16 M) and butanol (0.33 M) at 50 degrees C and agitated with 10 mg lipase. The decrease in butyric acid is measured by titration and 1 unit of lipase activity is defined as 1 mu mol butyric acid consumed per min per mg lipase.