1. Pull grapes from stems, rinse, and set aside about 2 cups. Put remaining grapes in an 11- to 12-inch nonstick frying pan.
2. Peel shallots and coarsely chop. Add to frying pan.
3. Cover pan and cook over medium-high heat until mixture is juicy, about 10 minutes. Uncover and boil over high heat, stirring often, until grapes begin to collapse and most of the liquid has evaporated, about 5 minutes longer.
4. Push grape mixture to one side and lay sausages in pan. Cover and cook over medium heat until mixture is juicy, about 10 minutes. Uncover, turn heat to high, and stir grape mixture often as it thickens and concentrates. Also turn sausages as needed to brown lightly. When grape mixture is richly browned, in about 10 minutes more, transfer with sausages to a platter and keep warm. Cut sausages in half lengthwise if desired.
5. Pour reserved grapes into pan, return to high heat, and shake pan frequently to rotate grapes; heat until they turn slightly brighter green, about 30 seconds. Pour over sausages. Season to taste with salt and pepper.