Charcoal is burnt wood. Why does it burn hotter?

The full narration of the video.

It takes five kilos of wood to make one kilo of charcoal, yet charcoal burns far hotter. Skewer stalls and copper hotpots all cook over charcoal. Start with the result: fan charcoal and it passes 1,100 degrees Celsius, hot enough for ancient smiths to smelt iron.

A wood fire? Tall flames, choking smoke, and heat that comes and goes. Same tree, so why is it hotter as charcoal? Let's rewind and see how charcoal is made. To make charcoal, you seal wood in a kiln with barely any air and let it smoulder for days.

Water leaves first. Even dried firewood is about one fifth water by weight. Next come flammable gases. Most of the wood drifts off this way. What's left is a black skeleton made almost entirely of carbon. That's charcoal.

It's a bit like reducing a sauce: the water boils away, a pot shrinks to a bowl, and every spoonful is richer. Charcoal is the same: kilo for kilo, it holds nearly twice the heat of dry wood. But reducing only removes water. The kiln also drives off those flammable gases, which could have made heat too.

Add it up: turning five kilos of wood into one kilo of charcoal spends more than half the heat inside the kiln. This step has a name: carbonization. Reducing stands for carbonization, what boils off is the water and gas, and the rich sauce left is this lump of charcoal.

Snap a lump open and you can still see the growth rings and grain. So why is charcoal hotter? Back to the skewer stall, and watch two fires burn. Lit firewood first spends heat drying out its own water, and that heat flies off as steam.

Then the heated wood gives off gas, and the gas catches fire in the air. That's the flame you see. The flames float above and mix with lots of cool air, so the heat spreads out, and whatever doesn't burn becomes black smoke. Charcoal skips all that. The water and gas were driven off back in the kiln.

Air touches the charcoal's surface directly, carbon and oxygen join right there, and the heat is released on the lump itself. So charcoal barely flames. It glows red all through, with the heat packed into one small spot. That's exactly what skewers need: steady heat, little smoke, rising straight up from below.

In fact, a wood fire gets there on its own in the end. Late at night, when a campfire's flames die and only a red glow remains, it's burning the charcoal it made of itself. Where have you seen a fire end as nothing but a smokeless red glow?