In a slow cooker, combine apple cider and cinnamon sticks.

Place whole allspice and cloves in the center of an 8-inch square piece of cheesecloth. Gather the edges of the cheesecloth and tie to secure, then place it in the slow cooker.

Stir in brown sugar.

Cook on High, covered, until the mixture is steaming and the sugar has dissolved.

Reduce heat to Low and keep warm.