Minecraft wiki entry for Smelting, associated text: To use lava efficiently, keep the remaining load of 36 or 16 items handy, and put it in during the middle third of the burn (after it has done that many, but before it exhausts the original stack). Remember to both refill the un-smelted items, and remove the smelted product. A despawn timer on a note block may help. Note:The numbers shown here is to indicate how many of the items to smelt,item stacks over 64 is not possible without cheats.