Mash 6 cups raspberries (about 700g); 2 cups sugar; 2 tbsp peeled fresh ginger, grated, and a pinch of salt until mostly smooth. Refrigerate for 1 to 2 days. Strain mixture into a medium bowl. Discard solids. Stir in ¼ cup cider vinegar. Makes about 2 cups. Syrup can be refrigerated for up to 6 months.