Sort the berries, rinse gently and drain. Mix in a bowl with the lemon juice and about 3 tablespoons of sugar, mash a little and let it steep for a few hours.
Pour the fruit mass into a cheesecloth or juice cloth. Collect the juice from the cloth in a bowl overnight.
The next day, mix the juice obtained with the remaining sugar and cook for about 5 minutes until the sugar has dissolved and the liquid has become thick. Then skim if necessary.
Fill the syrup directly to the brim with the prepared bottles, close and store as dark and cool as possible.