The best source I know on how to make Italian ice cream is Angelo Corvitto. His book ‘The secrets of ice-cream’ (Spanish/English) is out of print but you might find it second hand or for download somewhere. read more
You can tell when the gelato is done, by simply checking the consistency through the opening on the top of the ice cream maker. You will also hear the motor straining, as the gelato freezes. On some units, the directions with the maker tell you to let it work until the motor stalls and stops. read more