Natural charcoal is the result of heating plant or animal matter until moisture and impurities have burned off, leaving mostly carbon and ash. Many forms of charcoal exist, and commercially available charcoal is usually an admixture of char, ash, and either wood or cornstarch.
Charcoal almost always has some impurities, though sugar can be mixed with sulfuric acid to produce nearly pure carbon. To produce charcoal briquettes or lumps, the original organic matter must be processed. Charcoal lumps are made from sections of hardwood that are heated for several hours in an oxygen-free furnace to prevent combustion as the impurities are cooked off. The material that emerges from the kiln is mostly molecular carbon, with some ash, that is ready for use in a grill.
Briquettes are more complicated to produce than lumps. The manufacture of briquettes begins with charcoal that has been ground into powder. This dust is then mixed with sawdust or cornstarch, as well as adhesives to bind the briquette together. It is then shaped and heated for a few hours to harden. Some charcoal briquettes have additional components, such as fast-lighting briquettes, which have been soaked in volatile fuel that releases easy-to-ignite vapors for a fast burn.