Minecraft wiki entry for Experience_farming, associated text: Fuel can be provided by the player in quantity, but it is even possible to fuel the farm with an automatic bamboo farm, or with an automatic charcoal smelter, perhaps fed by a tree farm. An automatic charcoal smelter can smelt 7 stacks of material for each stack of wood provided to it; dried kelp blocks are more efficient at 20 input stacks per kelp-block stack (11, if we discount the kelp blocks used to smelt more kelp), but they do require manual crafting to produce. A bamboo farm must be large enough to provide four stacks of bamboo for each stack of material to be smelted.