Charcoal is carbon residue from material burned with limited access to oxygen, which facilitates the process of carbonization. While (in theory) almost anything with carbon content could be made into charcoal, in practice charcoal is most often made from wood, coconut shell, or other materials that start out with a high percentage of carbon, are readily accessible, relatively inexpensive, and burn easily.

The process can be as simple as burying a small amount of burning wood and letting it smolder, or as complex as the highly industrialized production of commercial charcoal briquettes. No matter how it’s done, the process consists of heating the material to first drive off the water. Once that’s done, as the temperature rises the material breaks down and releases tars and gases including hydrogen, carbon monoxide, and carbon dioxide. As carbonization occurs, the available oxygen is used up, which encourages further carbonization.

How far that process is carried determines the quality and yield of the resulting charcoal. Great charcoal consists of as much carbon and as little “other stuff” as possible. Needless to say, as with almost all things in the real world, there is a tradeoff. Low quality gives high yield; high quality results in lower yield, as increasing amounts of the volatile tars and gases are driven off. Making good charcoal is like burning money!

At 300 degrees centigrade, the resulting charcoal is approximately 68% fixed charcoal and 32% volatile materials (numbers rounded). The tars that linger are acidic and thus corrosive (and unlike cigarettes, there are no “filtered” charcoal briquettes!). These residual substances cause the charcoal to burn with a lot of smoke, and the tars are nasty and hazardous to your cooking and perhaps your health. They add off tastes, and create unpredictable cooking conditions, as well as causing sparking and unwanted flames.

At 700 degrees centigrade, about 93% of the resulting product is really charcoal, with only 7% volatile material. At the 300 degree temperature, more than 40% of the dried material you put in comes out as charcoal; at the 700 degree temperature, that drops to around 30%.