In a medium saucepan, combine cranberries, orange zest, cinnamon, orange juice and brown sugar. Add enough water to cover, and bring to the boil over high heat. Immediately reduce heat, and simmer for about 1 hour, or until the sauce has thickened. Taste for sweetness, and adjust with additional sugar if necessary. You cannot overcook, so continue cooking until you have a good thick consistency. Let mixture cool, then refrigerate in a covered container.