In large bowl, crush berries and sugar with potato masher. Add to lined slow cooker and stir in 1 qt. water, peppercorns, bay leaves and lemon zest. Cover and cook over low heat for 2 1/2 hours. Stir, increase heat to high and cook for 1 1/2 hours. Strain through fine-mesh sieve without pressing on berries. Stir maple syrup into blackberry juice and let cool. Stir in brandy, if using. Refrigerate up to 1 month. Makes 6 cups.