I always use 3 l schnapps bottles from the catering trade as a container.
Alternately fill the bottle with the cold washed and drained blackberries and the rock candy in 3 steps.
Cut the vanilla pod lengthways, open it a little and add halfway through the filling. Then pour in the brandy and the wheat grain. Close the jar with a cork (champagne corks fit with 3 l bottles) and turn a few times so that everything mixes a little.
Store in a dark room at approx. 20 degrees for at least 6 weeks and turn a few times every 2-3 days.
At the end of the storage time, pour first through a coarser tea strainer, then through a tea strainer and fill into bottles of the desired size.