Rinse the elderberries, drain thoroughly, and remove from the vine. Cover the berries with water, and bring to a boil. Cook until the berries begin to break down, then remove from the heat. Pass the mixture through a fine strainer lined with cheesecloth and drain overnight.
Weigh the juice, then mix with 500 g (approximately 18 ounces) per liter of juice. Simmer the mixture for 15 minutes. Fill the prepared bottles with the juice and seal immediately. Dilute the juice with some water before serving.