In a slow cooker or medium stockpot, combine the grape juice, cinnamon, star anise, allspice, ginger and grapes. Bring to a simmer. Turn off the heat and let steep for at least 20 minutes before ladling into mugs.
Adapted from "The New Midwestern Table" by Amy Thielen (c) Clarkson Potter, 2013. Provided courtesy of Amy Thielen. All rights reserved.