Making charcoal is a centuries-old technique that drives water and impurities out of organic plant matter like wood, or animal matter like bone, for a smokeless fuel that burns at a steady high temperature for long periods of time. The process that creates charcoal is called pyrolysis and modern charcoal-making methods haven’t changed significantly over the years.
It involves drying the matter and subjecting it to 450-510 degrees Celsius (840-950 degrees Fahrenheit) in a kiln. The wood etc is then left to cool and, after the oxygen is removed by shutting air vents, the material gradually turns to char.
Modern charcoal briquettes – the kind you can buy for your barbecue – aren’t the pure char that comes out of a kiln. It’s often crushed and mixed with other ingredients like sawdust or coal plus binder additives like corn, before being pressed into blocks and passed through a dryer.