Blackberries contain a wide array of important nutrients including potassium, magnesium and calcium, as well as vitamins A, C, E and most of our B vitamins. They are also a rich source of anthocyanins, powerful antioxidants that give blackberries their deep purple colour.Blackberries aren't a quick-drying fruit, because each of the juicy little globes that make up a berry has a thin, waxy coating.Dehydrate the berries until they're uniformly tough and leathery, almost hard.