Combine the paste ingredients, and then rub the paste all over the pork tenderloins. Allow the pork to stand at room temperature for 15 to 30 minutes before grilling.
Prepare the grill for direct cooking over medium heat (350° to 450°F).
In a medium bowl whisk the marinade ingredients. If the grapes are in one large, dense clump, cut them apart into smaller bunches for more uniform grilling. Add the grapes to the bowl and turn to coat them with the marinade.
Grill the pork over direct medium heat, with the lid closed, until the outsides are evenly seared and an instant-read thermometer inserted into the center reads 145˚F, 15 to 20 minutes, turning two or three times. During the last 8 to 10 minutes of grilling time, lift the grapes from the vinegar mixture, reserving the marinade, and grill them over direct medium heat, until lightly charred and just beginning to burst, turning once. Remove the pork and the grapes from the grill. Let the pork rest for 3 to 5 minutes.
Using kitchen shears, snip the grapes into small clusters for easier serving. Return the grapes to the marinade and gently stir to coat with any residual marinade. Cut the pork crosswise into ½-inch slices and drizzle with any accumulated juices. Serve warm with the grapes, and garnished with rosemary sprigs if desired.
Note: Choose small grapes, as the larger ones take much longer to grill and end up a bit mushy.