Friday, March 3, 2017

Complete combustion of incomplete combustion: Charcoal making preparation

Winter is the time for charcoal making. At the bottom of Ikebuchi Open Space, where Lovers of Niiharu meet at 9:00 every weekend, there is a hut. It looks like a garage with 2 mini-pickups of the Lovers parked regularly. The structure is actually a charcoal hut for 2 kilns. The idea of Niiharu Citizen Forest is to recreate traditional husbandry of forests in Yokohama. Charcoal cooking was one of the important jobs before the domination of fossil fuels. 20 or so years ago, the current chairman of the Lovers, Mr. Okawa, attended classes organized by the City, and transferred the knowledge, including a blueprint for kiln, of charcoal making to the other members. Since then, several members of Lovers are cooking charcoal in the facility every winter. The kilns have already accumulated the tradition of the Lovers.

Here it is.

There are many designs for modern charcoal kilns in Japan. (Photos can be seen here.) Niiharu’s kilns are different from that of Araizawa, or of Nature Sanctuary. Basically, it is made of a drum of 57cm of diameter and 90cm tall, buried in red clay. As this is for weekend forest volunteers, it’s not for cooking wood charcoal for days, but for one day making with bamboos. Even though, I am impressed with its clever low-tech, and sustainable for volunteers, structure. The bottom of a drum has a hole of 11cm diameter. The bottom wall of the drum also has 4 holes each of which has a welded pipe of 5cm diameter. The top of a drum is a lid with a hole for a Ø3cm pipe. The drum is then put on a U shaped concrete gutter as its Ø11cm hole is over the trough. The drum and gutter are held by red-clay loaded in a space surrounded by 4 150cm*120cm metal walls. The clay holds the drum and 4 pipes by piling up the square tightly to the rim of the drum. So, when we see the kiln from a side, it looks like a metal box situated on a clay mount with 4 pipes sticking out from the top.

Seeing a Niiharu charcoal kiln from the side
A sectional view of Niiharu’s charcoal kiln
It’s a view from the above of the kiln.

The science of charcoal making is, when we add heat on logs slowly but continuously in an almost sealed-up space, they start to heat up themselves and release volatile substances their cells hold. If we keep burning them by firewood, they will eventually become ashes which are the materials, such as metals, that cannot evaporate with the energy created by camp fires. In contrast, if we stop adding external energy, but create tightly sealed environment for the heated logs, they continue to burn themselves slowly with very limited supply of oxygen and discharge instable oils from their body as much as possible. Though, without new fire supplied, the closed structure eventually cools down and the self-combustion of logs inside also stops. The logs burned in this way end up as a chunk of carbon. They are now charcoals which are incompletely combusted logs in a shut room. When a charcoal is very close to pure carbon, they do not contain volatile element much. Unlike firewood, they can burn for a long time without creating flame. That’s why before Japanese valued good quality charcoal as energy source. In other words, a charcoal kiln intends to let the logs free the unstable elements completely during combustion. Niiharu’s kilns are designed to do that just by burning firewood in the concrete gutter.

The difference between completely burned woods and charcoal.
One of my senior Lovers showed me how different they were.
Completely burned woods looked like a charcoal,
but they were very fragile and easily became ashes
just by rubbing them between the fingers.
In contrast, our bamboo charcoal maintained its form
and emitted metallic sound when we gently tapped them.

To prepare charcoal cooking, the Lovers install a stovepipe that fits snuggly to the hole at the bottom of the drum. We then fill the drum tightly with sticks of bamboos. They are not just any trees from bamboo forests. We have to burn them for quite a long time, if not for days. So, if a bamboo is too thin, it would easily turn into ashes. We deliberately choose a large tree with thick enough wall. Moreover, a wet log is not for efficient combustion. We start to harvest bamboo logs in autumn before actual charcoal cooking begins and let them dry in a shed for at least one month. This requirement effectively excludes first-year trees for harvest since they contain lots of moisture. We cut the harvested logs in 53cm, i.e. the same length of the pipe at the center. It is possible to make a bamboo charcoal with the logs cut in this way which is called Hanazumi 花炭, or we split the logs to create sticks. As inside of bamboos are chambers void of tree meat, charcoal making with bamboo logs takes fewer hours, but the volume of product from one operation is smaller. We also have to be careful for burning firewood as bamboo-log will easily turn into ashes. We can stuff the drum with a larger volume of bamboos in the form of sticks, but it takes more time to make charcoal. Niiharu Lovers normally cook bamboo charcoal sticks, and make log charcoals when there is a special order.

Inside of a drum.
The center is a hole for stovepipe.
The wall of the drum has 4 holes where pipes are welded to.
Removable stovepipes
It fits to the hole like this.
Drying bamboos.
Not all of them are for charcoals.
We choose suitably-sized logs for preparation.
Cutting the logs to the size
We then split the logs to make sticks.
Bamboos are funny.
They can be cracked easily
when we strike vertically with a machete.
I learned the true meaning of Japanese phrase,
“his/her character just like splitting a bamboo
Dividing a bamboo log is really “with a good grace.”
We made lots of bamboo sticks ...
and stuffed them in the drum ...

The pipes welded at the bottom wall of a drum have important function. To make complete combustion of incomplete combustion, we have to let the volatile substance inside the bamboo free to evaporate. The pipes are for these gasses to escape from the drum. Before stuffing the drum with bamboos my senior Lovers cleaned the pipes carefully to remove clogs. After filling the drum, a lid is put on it and sealed with the red clay mud to establish the flow of heat one-way, from the gutter to 4 pipes, as much as possible. After 17 years of operation, the supply of red clay becoming somehow smaller, the seniors say. Red clay is typical soil in Kanto region especially where the volcanic ashes from Mt Fuji fell when it erupted. I asked if we can just dig up the land wherever allowed in the Niiharu Forest to replenish the stock. “Huh? Of course not. Niiharu is rich forest with lots of fallen leaves and the other organic materials. When we use the soil from here directly, those organic materials will be burned during the charcoal cooking, and the mud cannot seal the kilns tightly.” Oh, I see.

Cleaning the pipes …
and drums.
When we opened the lid at the beginning of the season,
inside of a drum was a home of a cricket.
Cute. 😄
Making red clay mud for sealing.
Shutting the lid tightly, and
Sealing it with clay mud.
The stick over the lid is a pipe for inserting a thermostat
during the operation.
We pile up the mud over the lid further …
until the kiln looks like this.

The volatile compounds vaporized during charcoal making are that problematic smoke the Hikarigaoka Housing Complex complained to the volunteers of Shikinomori Park. It is that much. It cannot be dealt with the tiny 4 pipes poking out from a drum. In addition, when the vapor cools it becomes useful wood vinegar so that we want to catch it while its cooling. The Lovers mount extensions of the pipes. Here is another clever way Niiharu employs for charcoal cooking. We went into bamboo forest and harvested 3 to 5 years old large bamboo logs with 15cm or so diameter. With a long metal pole, my seniors punched the wall of each node that separated sections inside of the harvested bamboo logs. Voilà! Long bamboo trunks turned into long chimney pipes. According to the seniors, a bamboo chimney works well for about 2 seasons. When it’s time to replace, we simply return them to the forest, and they go into mulch over the ground. Meanwhile, the supply of new boles is not the issue thanks to vigorous bamboos. Sustainable, isn’t it?

New chimney pipes
The end of each bamboo pipes
are cut like these …
And set up at the pipes coming from
the bottom of the drum like this.
A shorter log of a bamboo acts like a bucket.
When the fume comes out from the drum,
it cools down rapidly by winter air, and liquefies.
It’s original solution of wood vinegar
that is to be collected with this bamboo bucket.
The bamboo pipes extend out of the hut.

Now, we are ready to start cooking! I tell you my whole day adventure of charcoal making next week. 😊

If you find a problem in Niiharu Forest, please make a contact with

Office for the Park Greeneries in the North 北部公園緑地事務所
Yokohama Municipal Government Creative Environment Policy Bureau 横浜市環境創造局
Phone: 045-311-2016 (I guess in Japanese only)
FAX: 045-316-8420 (I hope there is somebody who can read English …)

Niiharu Administrative Office / Satoyama Exchange Center 新治管理事務所・里山交流センター
Phone: 045-931-4947
Fax: 045-937-0898

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