After some thought and some research, I’ve changed my mind about buying lump charcoal. It really isn’t that hard to make your own but there are some “start-up” costs involved. Humans have been making charcoal for thousands of years and it is likely that the dark soils known as terra preta in the Amazon (and found in many other locations world-wide) are the result of centuries of human habitation in one place. I have read, contrary to what is commonly thought, that the Amazon basin had a substantial indigenous population prior to the arrival of Europeans and their diseases. Epidemics of diseases that the indigenous people had no immunity to wiped out the populations in a matter of decades. Similar events occurred in North America. So the conclusions that the anthropologist Betty Meggers arrived at (that the poor soils of the Amazon rain forests could not support dense concentrations of humans) increasingly appear to be based on faulty interpretation of the data. But I digress – this post is about how to make biochar, not about the demise of indigenous populations.

Charcoal is made by heating wood to break the chemical bonds that make up cellulose and to drive off the resulting gases and tars. The heating is done in an oxygen-deprived environment so that only the carbon in the wood remains. If you would like to view an interesting series of videos showing how charcoal was made up until the 1850s in Pennsylvania, click on these links: Part 1, Part 2, Part 3, and Part 4. This series of videos is from a 31 minute documentary made by Van Wagner and is a “historical re-enactment” of how charcoal was made in the “good old days” which were not all that great! It is an entertaining series of videos to watch but not something that would inspire me to go out and make charcoal that way!

There is a better way – a way that does not pollute the environment as badly as the traditional direct method of making charcoal does. This method is the indirect or “retort” method and involves “cooking” wood in a container with an outside energy source to drive off the gases and create charred wood. A retort is simply a sealed container of some kind that can withstand the heat of the external fire and allow the gases created by that heat to escape. For an overview of what is involved, I recommend looking at Daniel O’Connor’s site. There are improvements that can be made in the way he has created his retort, but they cost money. You will note that Daniel has used concrete blocks to build his enclosure. It has been my experience that concrete blocks don’t last very long when exposed to a wood fire – they crack and disintegrate. You will also notice, in one of the pictures, that the pipe that supports the drums has bent under the weight of the drums and the heat of the fire. A better method of constructing this kiln would be to use refractory brick and a thick steel plate to separate the drums from the fire underneath. But the principles that he is using are sound – the gas that is driven off by the heat of the external fire is carried via the pipe back down into the combustion area, where it is burned instead of escaping into the atmosphere where it would be a pollutant.

I think that a combination of the kiln-building expertise of wood-fired potters, the skills of a welder, and the enthusiasm of gardeners who want to use biochar in their gardens would result in a long-lasting retort that could produce biochar for an entire community.