Thursday, December 9, 2021

Charcoal, part 3: Production

Charcoal has only a minor market presence in modern America, where we have abundant electricity and petroleum for our heating and cooking needs, but it is a staple in Africa, Asia, and the Middle East. There are some restaurants that prefer to cook over charcoal due to the even heating and lack of smoke, so there may be a market in your area if you're looking for barter opportunities. When TSHTF, we may find ourselves without access to pipelines and powerlines to keep our families warm and fed, so I feel it's a good idea to look into alternatives. 

Making charcoal isn't hard; you're basically slow-cooking some organic form of carbon, usually wood, to drive off the water and volatile chemicals. Humans have been making charcoal for use as a fuel for 30,000 years, so it predates agriculture by quite a bit. If an uncivilized, nomadic, tribesman can figure it out it shouldn't be too difficult for us.

If you're starting with wood, this is the first step in "wood gasification", a method of producing a flammable gas (mostly carbon monoxide) that is suitable for fueling internal and external combustion engines (people have run cars on wood gas when petroleum was unavailable or too expensive) or burning in lamps. The houses of a century ago had gas lamps on the walls and "manufactured gas" was piped in as a city utility. Manufactured gas, made from coal, wood or oil, was more dangerous than methane as the carbon monoxide content was high enough to cause poisoning if a lamp or valve failed.* The low pressure that the gas was delivered at caused already-lit lamps to dim if another one was turned on; this was the basis for a play and movie that gives us the term "gaslighting" for psychological manipulation of people.
*Now you know why we call the methane extracted from underground and piped to our houses "natural gas". 
Wood that contains a large portion of resin can also produce a variety of useful byproducts like pine tar that are used in other industries. Methanol, sometimes called "wood alcohol", can be distilled out of the vapors and has several chemical uses; in fact, it was one of the first forms of antifreeze used in cars. Capturing the vapors and condensing out the useful compounds is a bit more involved than most of us want to get, but the option is there.

Charcoal production is simple, but very time-consuming and labor intensive. Depending on the size of the operation and techniques used, a batch of charcoal will take between 1 and 20 days to produce. That's a long time to babysit what is essentially a smoldering fire, but it is not a process you can start and walk away from. You'll need a supply of wood or other high-carbon feedstock (corncobs, coal, and bones work well), an air-tight container referred to as a "retort", a way to control the air going into the retort, and a source of heat. If you've ever used a flint and steel to start a fire you may have seen charcloth used to catch the sparks. Charcloth is the result of making charcoal out of cotton cloth, and I'll us that as a demonstration since it can be done on a small scale.
  1. Start with a clean, empty paint can with a lid. 
  2. Loosely place a good pile of pure cotton cloth scraps (any size or shape works because you can cut it easily later) into the can and place the lid on tightly. 
  3. Using a nail or small punch, make a small hole in the lid to let the air and vapors out. 
  4. Place the closed can on or near a small fire, watching the color of the vapors that come out of the hole in the lid. Slow gentle heat is best, as you don't want to create so much pressure inside the can that it pops the lid off. 
  5. The first phase will be drying the feedstock and the vapors will be mostly water vapor (steam) so it should be whitish in color and won't burn. 
  6. Once the water has been driven out, the plume of vapors will change color or lose its color. This is the stage where volatile chemical are being released from the cloth and these vapors will burn if a flame touches them. I've seen people intentionally light the plume of vapors at this stage as a way to tell when the process is done;  the flame will go out once all of the volatiles are driven off. 
  7. When the plume of vapors stops coming out of the hole, the hole in the lid is closed off with a dab of mud or clay and the can is removed from the heat and left to cool. 
  8. Your charcloth is ready to add to your firebox after it cools. Opening the can while it is still hot will let oxygen in and cause a flash fire, reducing your charcloth to ashes and probably making you change your underwear.
Production of charcoal uses the same steps, just on a larger scale. 
  1. Simple kilns are no more than stacked firewood that is covered with straw and mud, leaving an opening at the base for lighting and a chimney to let the vapors out. 
  2. The burning of a portion of the stacked wood provides the heat to convert the rest into charcoal, the mud forms an air-tight enclosure, and the two holes are used to control the airflow through the pile. 
  3. The size of the pile of wood determines how long the process will take; it will be measured in days, and someone will have to keep an eye on it the whole time to adjust airflow, monitor the vapor plume, and repair any cracks in the mud shell that will occur as it heats and dries. Unless you can stay awake for days, plan on having a team to get best results. 
  4. Once the process is complete, both holes are sealed up to quench the fire and the pile is left to cool for a few days. 
  5. After everything has cooled down enough to work with, you'll break away the baked mud shell and harvest the charcoal. Any wood that didn't get completely converted gets set aside for the next batch.
More modern kilns are made of metal or brick and have better methods of controlling the airflow, and loading and unloading is much easier and cleaner. Most commercial operations will have multiple kilns running at different stages to make production more steady, loading one while others are burning, still others are cooling, and one is being unloaded. 

This post turned into the biggest rabbit hole I've encountered in the almost eight years I've been writing for this blog. The amount of information available on charcoal production is mind boggling, from ancient methods and archeological research to modern methods being developed for impoverished areas, efficiency of internal heat versus external heat, yields from various types of wood or other organic matter, then branching off into bio-char production for improving cropland and that leads off into other fields of research.

If you're interested in more detailed information, let me know and I'll cover some of the more readable sources I found.


  1. I'm seriously interested. Could you give us a quick bibliography?

  2. This reminded me of a couple of sources on charcoal for gunpowder. One is a pretty good book, 'Like Fire and Powder', which covers his whole process for making and what woods he's used for his carcoal.

    The other is on Project Gutenberg, 'History of the Confederate Powder Works'. Good piece on their whole process, and how they settled on cottonwood as their preferred wood.


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