Pour cider into crock pot. Stir in brown sugar. In a coffee filter or cheesecloth, place the allspice, cloves, cinnamon and nutmeg. Carefully fold up the coffee filter, making sure none of the spices can fall out. Tie up with butcher’s twine and place into the cider. Slice an orange in half and place sliced side down into the cider. Cover and heat on low for several hours before guests arrive, or can be heated on high for an hour or two until it’s hot enough and then turn the heat down to low. Keep spice bag and orange halves in the cider the entire time.