I used to make and sell charcoal at the farmers market. I'd seen it made as a kid. This is something anyone can do, very simple. It's not a new process, retorts have been used for hundreds of years. This was a prepping project. I thought this would be a necessary skill to have. I always try to figure a way to earn cash from my projects. People who bought my charcoal were paying me to improve my method and gain experience.
Charcoal, I can cook without flames, filter water, it has medicinal use and it's one of the 3 ingredients of black powder.
There are 3 Main Components
1. The Furnace - I use an "Open Head" 55 gallon steel drum. The lid is held on with a quick lever closure ring or a nut and bolt closure ring. I prefer using the quick lever rings. The removable lid is used to help regulate air flow during the cook.
I cut 3 air vents at the bottom edge of the barrel. They are equally spaced around the circumference. Each vent is about 8 inches long and 2 inches high. I leave the metal connected at one end so they can be partially closed/opened to control air flow during the process.
2. The Retort - I use a 15 gallon steel drum with a crimp type lid. The ones I use are about 24 inches tall and 14 inches in diameter. The lid is used during the process.
The retort must be vented to allow gas to escape from the wood while it is being converted to charcoal. In the bottom I drill 1/4 inch diameter holes, 30 or so is plenty.
Steel Drums - They can be purchased new from and oil distributor or gotten used from trucking companies or large farms etc. I'd get used oil or grease drums then burn out the contents. I wouldn't use a small drum that held unknown chemicals or came from unknown source. It will contain the charcoal used for cooking and water filtration.
3. Fire bricks - I use 3 to raise the retort a couple of inches.
Wood - 2 main types
Hardwood - Any quality hardwood makes great charcoal, various oaks, hickory's, even maple. The properties vary with the type of wood. I experimented quite a bit and settled on red oak. It turns out very pitted with large cracks. It is easy to light and produces a very even burn. It's also great for water filtration. For black powder muscadine or grape vine is recommended.
I cut logs and allow them to dry 9 months or so. I cut discs, 5 inches long, off the end of a log. I quarter and split it into 1.5 inch thick bricks. Using a hand ax I cut the bricks into pieces 1.5 inches X 1.5 inches X 5 inches. If the pieces are larger it just adds unnecessary cooking time and wastes more scrap wood.
Tips on tree selection - Pick a tree that grew at least 100 yards from any open area among older trees. It would have grown tall and fast, with very few knots. Perfect for splitting! A tree at the edge of a field would have grown with lots of limbs, way too many knots for easy splitting.
Scrap wood - You'll need tinder and some hardwood as it produces a steady even heat. I use last year's firewood. I also use small pieces of scrap pine lumber. It produces quick heat helping to regulate the cooking process. Everything is split small enough to go in between the sides of the barrels no longer than 2 feet.
1. Put the fire bricks in the bottom of the furnace to support the retort. This allows space for out gassing and also prevents the ground from wicking heat from the retort.
The hot gases leave the retort before contact with oxygen. After they exit they burn. This burning gas cuts down on the total amount of scrap wood used. When out gassing starts you will really be able to feel the heat coming off the furnace. These are the same gases used to run a wood gas engine.
2. I occasionally shake the retort while loading it. This settles the pieces and insures as much wood as possible is cooked per batch. It also leaves little space for oxygenated air. Put on the lid and clamp it tightly. Don't force it, take out a few pieces if necessary. Set it on the fire bricks. It should weigh about 55lbs.
There will be a brief flash burn in the retort at some point early in the process. It doesn't harm the wood. This burn leaves no oxygen in the retort. As the wood is heated it begins to out gas. These gases don't burn until they exit the bottom of the retort. This is why the retort wood isn't consumed.
3. Next I drop kindling down the outside of the retort and then scrap wood up and over the top. I stuff paper and tinder into the furnace vents and fire it up!!!
Cooking - Moisture is your enemy!
The goal is to hold 700 plus degrees in the retort for at least 1.5 hours. Low moisture content is very important. High moisture content adds more time and scrap wood to the process. This is why I cut logs 9 months in advance.
I use the lid of the furnace to hold heat in but not so much as to kill air flow. I raise the lid just a little with re-bar or wood pieces. I also move the lid around while adding wood and making sure scrap is burning evenly. The scrap wood also took work to produce. I try not to waste it.
As the burn progresses ash and coals begin to drop to the bottom of the furnace. It will start to clog the 3 vents. I push the ash back a little keeping the vents clear. This also helps direct the air flow up and away from the bottom of the retort.
Afterwards - When I think a batch is done, I put the lid on the furnace and tighten the band. I close the bottom vents on the furnace and cover them with dirt. This stops all air flow. I don't allow the scrap to burn out. When I decide the charcoal is done I seal the furnace. The burning scrap will use up all remaining oxygen in the furnace and prevent charcoal loss.
I always leave the air tight furnace to cool over night. If exposed to oxygen the hot charcoal will ignite and burn up. The next morning I open the cool furnace and remove the retort. It should weigh about 22 lbs, if it feels a lot heavier the wood did not completely convert to charcoal.
I open the retort and filter the contents with a framed 1/4 inch screen to get rid of tiny pieces and dust. I get about 18 lbs of high quality natural charcoal.
There is an art to this! You have to learn to read the smoke.
The first smoke will be heavy and white. This is moisture from the scrap wood. It will continue for a while then tapper off. A few minutes later white smoke will reappear but not as heavy as before. This is moisture from the red oak in the retort.
Important!!! The amount of white smoke from the retort indicates how long to burn scrap. Only experience can teach you how to judge this! Don't worry too much, at some point you'll find a partially converted batch. You'll have to re-cook the same batch again, an invaluable lesson.
Sometimes there is a small amount of loss to ash, usually just on the surface of a few pieces at the bottom. A lot of ash is caused from not having the lid on the retort tight enough. Do not allow air to flow through the retort!
Though simple this is actually a very efficient process for producing high quality natural charcoal. I run 2 furnaces at the same time and produce about 35 pounds a day.
I can prepare all the oak and scrap for 2 furnaces and cook both batches in about 4 hours. Cooking with 2 furnaces has a big advantage. They will share radiant heat cutting down on the total amount of scrap used. I place them within 3 feet of each other.
When out gassing begins the temperatures are over 1000 degrees. Metal will begin to soften. It's difficult to feed and work the furnaces at these temps. I have to work quickly and be very careful!
I only make charcoal in hot weather, July or August. I pick a day when it's over 90 degrees and sunny. On a cloudy day when the temp was around 70 I used twice the scrap to cook the same batches. A big waste of time and effort.
Also, larger pieces of oak in the retort only added cooking time. It seems like a lot of work and time to prep small pieces and in the beginning it was. After a hundred pounds or so I was amazed how quickly it could be done AND keep all my fingers! This is why straight grained wood is important, it is easy to split.
Warning, use only natural unprocessed wood for charcoal.
I only get about 20 batches out of a set of barrels. Over time they will deteriorate because of the high heat.
One last thing, have plenty of aloe on hand. If you start making charcoal you're going to need some!
Filtering Water with Natural Charcoal
Some friends and I experimented with gravity filter systems. The 25 gallon tub's I buy cattle feed in work great, 5 gallon buckets too.
Local deposits of white quartz sands are plentiful. They are great to layer above and below the charcoal. Coffee filters work fine to keep sand and charcoal from leaving the container.
The goal with charcoal is surface area. I crushed the charcoal in fine pieces exposing more surface area to come into contact with water. This is why I use red oak, it's naturally pitted, naturally has more surface area.
I've read several "authoritative statements" over the years about how long such a filter will last. Basically 20 to 40 pounds of charcoal is needed to purify water for 1 person for a year. This all depends on how polluted the water is to begin with. Charcoal can only absorb so much pollution.
Chlorinated drinking water is a good way to test when a charcoal filter needs to be replaced. Occasionally run a batch of through the filter. When you start tasting the chlorine the charcoal needs to be replaced. It can no longer absorb contaminants.
A few photo's and notes.
Pic 01 - Stacked red oak disc's dried and ready to process. Maple and hickory are in the background. I experimented quite a bit that first year.
Pic 02 & 03 - Shows some knotty hickory that didn't split very well. Loading the retorts is next. The pieces in the retort are a little large for efficient processing.
Pic 04 - Shows some scrap pine I got from a local wood products company. I gave the owner a couple of bags of charcoal and he was more than happy to let me have all I needed. The quick burning pine is helpful in regulating the cooking process but white oak fire wood from last year is the main stay.
Pic 05 - I run 2 cookers at the same time spaced about 3ft apart. They share radiant heat. I produced about 35lbs of charcoal a day.
Pic 06 - Shows one of the vents cut into bottom edge of large barrel.
Pic 07 - Shows vent holes drilled in the bottom of the retort.
Pic 08 - A furnace and retort, 15 gallon drum with crimp on lid inside an open head 55 gallon drum.
Pic 09 - Here is about three pounds of the finished product. I purposely put aloe plants in the background. If you cook charcoal you're going to need some sooner or later.