Place Mulling Spices in the muslin bag (a large tea ball or cheesecloth also works) and simmer in 1 to 2 cups water for 20 to 30 min. This will reconstitute the spices. Discard the water but keep the spices. Pour the gallon of cider over the spices and warm the mixture. The spices will flavor the cider in about 15 min.
To dress it up, serve with cinnamon sticks and orange slices. You can also use a coffee urn to make mulled cider in larger batches for parties. Place the mulling spices in the top of the urn where the coffee would normally go (using 3 Tbsp. per gallon of juice). Pour the juice in the bottom of the urn and let percolate to mull the cider.