Wrap the cloves, star anise and cinnamon in a small square of cheesecloth and secure it with kitchen twine.
Combine the wine, sugar if using, orange zest, orange juice, rosemary and the spice pouch in a slow cooker. Cook on low heat until hot, about 1 hour. Adjust the slow cooker to the "warm" setting. Serve in mugs with a rosemary sprig as garnish.