Thoroughly rinse and dry the grapes, removing them from the stems. Using a paring knife, trim away the very end of the grape that was attached to the stem, exposing a bit of flesh inside. Fill a quart jar with the grapes and raw garlic halves.
In a medium saucepan, combine the remaining ingredients. Bring to a boil over medium heat. Cool the brine then pour over grapes (you can pour while still warm, but it will wilt the grapes a little). Chill the brined grapes in their jar in the refrigerator for at least 8 hours or overnight. Serve cold. Divine with a cheese course, sliced atop salads, or diced into chutneys.