Smelting

Smelting (or Melting, Baking, Cooking, Burning, Producing) is a method of producing refined goods in Minecraft. It has the same idea as Crafting; one must put in acceptable ingredients, and a corresponding output will be given. However, smelting utilizes Furnace blocks which have a unique interface. When right-clicked, a menu will come up where heating operations can be done. It consists of one field for the object that will be heated, one field for the fuel and one field for the output object.

To smelt something, an input material and fuel must be loaded in the Furnace. It will begin Smelting on its own and will continue to work if the menu is closed and the player leaves. When the Furnace begins heating, it will consume one piece of fuel and the fire gauge will fill up. As the input smelts, the fire gauge will slowly recede until it is gone, and then the next piece of fuel will be used. If there is no more fuel left, the furnace will be interrupted and the current item being smelted will be left un-smelted. However, if fuel is burning and runs out of input, the fire gauge will continue to burn down, wasting the burn time left. Once the fire gauge is out, no more fuel will be used.

As things smelt, an arrow icon represents the cooking process. Each smelting operation takes 9.25 seconds and the progress will be shown on the arrow. If the furnace runs out of fuel before the arrow is filled up, the input won't be smelted and will have to be redone. When the arrow fills up completely, one input item will be put in the output field as a output item.

If the player leaves Furnaces smelting and goes so far that the Chunks unload, the Smelting process will halt until they return. Smelting will also pause if one leaves the dimension the Furnaces are located. If the player sleeps in a bed while a furnace is smelting, the furnace's progress will be the same as if the bed hadn't been used and no additional time had passed. The reason for this is because when you sleep in a bed, no time actually goes by, but instead the game sets the time of day to morning.

Fuel efficiency
Each operation costs 200 units of heat. Sleeping while smelting/cooking items will not speed up the process.

History
Before the furnace appeared, smelting was accomplished by creating a fire and dropping the ore into it. During the Indev versions of Minecraft you started with a bunch of TNT and Flint and Steel which allowed you to smelt any ores before furnace was released. This method was hard and time consuming, and it is much easier to use the furnace to smelt items. Jeb has hinted at the possibility of adding portable fireplaces for use during long (nomadic) treks in which a furnace would not be feasible.

From snapshot 12w18a, wooden tools became able to be used as fuel for furnaces if players ran out of other fuel, didn't want to repair the tools or finish using them.

Trivia

 * It takes 10 minutes and 40 seconds to smelt a stack of 64 items.
 * Burning Wood with Wooden Planks to make Charcoal is over 5 times more efficient than using the wood itself as fuel. It is just over $1 1⁄4$ times more efficient than using planks.
 * Note that when using a bucket of lava for smelting, the bucket vanishes when used completely.
 * Jeb has stated he likes the idea of smelting Gravel to create "Stone Chunks", which could be crafted into Stone Bricks in a 2x2 grid.