Boil down rock candy and 100 ml water until the mixture has a syrupy consistency. Let the sugar syrup cool down. Sort the blackberries, wash thoroughly and drain well.
Pour it together with the grain, sugar and raspberry syrup into a well-cleaned bottle with a wide neck and close it tightly. Leave in a dark place for about 2 weeks. Shake from time to time. Then pour through a fine hair sieve and fill into bottles.
Tastes great as a drink topped up with sparkling wine or with ice.