About 3 1/2 pounds of mustang grapes (this can vary). Cover the grapes with water, using a large pot. Boil until the skins of the grapes crack. Mash grapes in a colander and save the juice. Puree the grapes for jam; strain for jelly. Mix 1/2 mustang juice and 1/2 Welch's unsweetened grape juice, or you can use all mustang juice. Follow directions in Sure-Jell box.