Famous for being the main ingredient in grape juice, Concord grapes are medium to large in size, round to oval in shape, and have thick, tannin-rich skin that offers a pleasant chewiness and varies in color from deep blue to purple or almost black. As for their translucent green flesh, it is juicy, almost gelatinous, and contains many large seeds. In addition, Concord grapes are in fact an excellent source of vitamin C and the phytonutrient, resveratrol, which in turn is an important chemical in maintaining heart health.