Define hydrolytic rancidity

Lipolysis is a major action occurring during deep fat frying due to large amounts of water introduced from the food and the relatively high temperatures used. Development of high level free fatty acids during frying is usually associated with foaming and a decrease in the smoke point of the oil and reduction in the quality of the fried food. The release of short - chain fatty acids by hydrolysis is  responsible for the development of an undesirable rancid flavour (hydrolytic rancidity) in raw milk. Furthermore, free fatty acids are more susceptible to oxidation than other fatty acids esterified to glycerol. 

Lipolysis, therefore, can cause changes in fats and oils which are best avoidable.  On the other hand, you would be surprised to learn  that certain typical cheese flavours are produced by deliberate action of microbial  and milk lipases. Controlled and selective lipolysis is also used in the manufacture of other food items, such as yogurt and bread.