Smelting

Smelting, also known as melting, baking, cooking, burning, and 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 object that will be output; for example, two saplings could be used to smelt one wood into one charcoal.

To smelt something, an input material and a fuel must be loaded into the furnace. It will begin to smelt on its own and will continue to work if the menu is closed and the player leaves. When the furnace begins to smelt, 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 raw. 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 10 seconds and the progress will be shown on the arrow. If the furnace runs out of fuel before the arrow is filled up, then the input will not be smelted and the process will have to be repeated. When the arrow fills up completely, one input item will be put into the output field as an output item.

If the player leaves a furnace while it is smelting and travels so far that the chunks unload, the smelting process will halt until the player returns. Smelting will also pause if one leaves the dimension the furnace is located in. If the player sleeps in a bed while a furnace is smelting, the furnace's progress will be the same as if the bed had not been used and no additional time had passed. This is because when a player sleeps in a bed, no time actually passes. Instead, the game sets the time of day to morning.

Fuel efficiency
Sleeping while smelting/cooking items will not speed up the process.

Note that after the fuel source has started burning, you cannot stop it from burning, so when burning with fuel sources such as lava, which, at maximum efficiency, can burn more than a stack of items, the items must be refilled. If the player were to enter 64 items and a bucket of lava, the lava would keep on burning long after the items are cooked/smelted. The amount of time that a fuel source will burn is always the same, but the amount of items that it will burn vary, depending on whether it is operated at maximum efficiency or not.

History
Before the furnace appeared, smelting was accomplished by creating a fire and dropping the ore into it. During the Indev versions of Minecraft, the player started with a bunch of TNT and Flint and Steel, which allowed for the player to smelt any ores before furnace was released. This method was difficult 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, did not want to repair the tools or finish using them.

As of 12w22a, the player gains experience orbs from using a furnace.

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.
 * Using a bucket of lava before Snapshot 12w22a would consume the bucket.
 * 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.