Lipases are carboxyl-esterases (EC 3.1.1.3.) which, in vivo, catalyze the hydrolysis of triglycerides and isoluble substrates by a heterogeneous process. In vitro, they may also hydrolyze soluble esters, but the presence of a water-lipid interface significantly increases their lipolytic activity. The commercially available crude lipase contains ca. 30% of lactose as 'extender'. In fact, the addition of sugars or polyols stabilizes the biological macromolecules, thereby preventing loss of enzyme activity and increasing resistance to denaturing conditions. By means of differential scanning calorimetry (DSC) and thermogravimetry (TG), it has been possible to evaluate the composition of a commercial lipase and also to demonstrate the addition of a monohydrate alpha-lactose, and the time of addition.