Preheat the oven to 450 degrees. Place the fruit and charcoal on ovenproof trays and bake for 1 1/2 hours. Turn the oven down to 300 degrees and then continue to bake the charcoal for 6 hours. Remove when the charcoal is black and completely hard.
To use, light a small amount of hardwood charcoal. When ashed over and ready to use, add the citrus charcoal and allow it to ash. Grill as you normally would grill.