Place allspice, cloves and cinnamon sticks in the center of a coffee filter or an 8-inch square of cheesecloth. Gather edges and tie with a small piece of kitchen string. Combine spice bag, pear juice and pear nectar in a 3-quart slow cooker. Cover and cook on low setting for 3 hours. Remove and discard spice bag but be careful because it’s really hot.