Fill 4 double old fashioned glasses with ice and set aside. In a pitcher or quart-sized mason jar, muddle rosemary (if you don’t have a muddler, use the end of a wooden spoon). Add cranberry juice and kombucha, stir gently to combine. Pour into ice-filled glasses, using a strainer if necessary. Garnish with sprigs of rosemary, a few cranberries, and thinly sliced fresh ginger (optional) before serving.