Charcoal Making – 炭焼き

Charcoal making experience was… a success!  A little over two weeks ago, I went to Shinkamigoto to make charcoal with Yo’s dad.  I have been interested in learning the process ever since I learned that Yo’s family still made and used charcoal for cooking.  I think that was almost three years ago by now.  Now it seems that Yo and I are nearly ready to start the transition towards cooking with charcoal ourselves, so I really wanted to take part in the making of it.

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Split bamboo lining the bottom

I’ll start from the beginning of the process, and explain what we did along the way.  I was actually there from the unloading of the third batch to the unloading of the fifth, so the photos are of different batches.  I’ll try to put things in an order that makes sense chronologically.

This charcoal “kiln” as I’ll call it, was built more than 20 years ago by Yo’s dad.  It’s been repaired over the years, but is still hard at work churning out several loads of charcoal a year.  The kiln is built into the side of the hill in front of the Utano household, and constructed of rock, earth, and fire-resistant plaster.

In order to prepare the kiln for firing, the first step is to line the floor with split bamboo.  This provides a space for air to flow beneath the wood, and keeps a small trench open for tar to drain away from the rear of the kiln.

You can see in the picture to the left that the chimney for exhaust smoke is located at the base of the rear wall of the kiln.  The chimney pipe is separated from the charcoal chamber and exits vertically through the earthen wall.

After lining the floor with bamboo, the next step is to load the wood into the charcoal chamber.

Loading the kiln, smallest diameter first
Loading the kiln under Utano san’s direction, smallest diameter first

The loading progresses from the rear of the kiln (farthest from the fire-box) with the smallest/thinnest pieces going in first.  Ideally these pieces are long and thin, and placed so that the direction the branch was growing faces downward.  This end of the kiln receives least heat, so the smaller pieces go here.

The kiln is then loaded all the way towards the front where the burn chamber is located. The size of the wood is gradually increased as you get closer to filling it, and the final two feet or so is filled with large, un-split logs.  The reason for the large logs at this end is that the fire-box is located directly on the other side of the wall, with an airway connecting the two chambers at the top.  This location receives the most heat and therefore should have the largest wood.

Care must be taken not to stack the wood to high in this kiln, as the roof is flat.  As he readily admits, a more efficient design would incorporate a domed roof, but the flat metal panels Utano san uses are easy to completely remove, thereby giving easy access for loading/unloading/cleaning the charcoal chamber.

Almost full!
Almost full!

Once the chamber is fully loaded, it is topped off with fresh Japanese cedar (Sugi) boughs.  These branches will ignite the fire in the charcoal chamber after the fire in the fire-box has burned long and hot enough.

Cedar boughs are laid on top of wood.  Edges are lined with clay and steel lids will be laid in place.
Cedar boughs are laid on top of the wood. The edges are lined with clay and steel lids are set in place.

The edges of the kiln are then lined with a row of sticky clay, on top of which the heavy steel panels are laid.  The line of clay helps prevent heat and smoke from escaping out the sides of the kiln.  Once the lids are in place, they are covered in a fairly thick layer of dry ash-like soil which further seals and insulates the chamber.  More ash can be added if smoke is leaking out once the fire is lit.  You can also see that the removable chimney pipe is installed in the photo to the right.  This is also sealed with the sticky clay and ashy soil.

Now comes the fun part, firing the kiln!  First, a thermometer is stuck at the top of the chimney pipe to read the temperature of the gases coming out.  Next, a fire is built in the fire-box and slowly built up until there is a good set of coals going.  When there are good coals and the fire is in no danger of being snuffed out, the fire-box is loaded up and allowed to burn very strongly.  The fire is continuously burned from this point on until the temperature reading on the thermometer starts to reach the upper 60’s celsius.  This usually takes several hours, but varies depending on a number of factors.  The fire is then maintained at this upper 60’s, lower 70’s temperature for a while, until the fire-box fire is allowed to diminish.  When the fire is allowed to reduce, and the temperature reading at the chimney does not drop over time, the charcoal chamber has successfully been ignited.

Beginning to stoke the firebox
Beginning to stoke the firebox

From this point on, the temperature at the chimney is held in check by blocking outflow of gasses at the chimney itself and by blocking air intake at the fire-box opening.

Eventually, many hours later, the temperature will begin to rise and continue to do so regardless of any airflow control.  When this happens, the process is nearing the final stage.

Utano san’s thermometer goes up to 200 degrees celsius, but eventually the temperature exceeds that.  When that happens, it’s time to watch the smoke.  When the charcoal is almost ready, the smoke should turn from white to a steady blue.  Since the temperature of the smoke is beyond what the thermometer can measure, Utano san has an ingenious way of determining when to seal the kiln…  he holds a match over the pipe and times how long it takes to burst into flames.  When the timing gets down to about 6 seconds, it is time to seal up the kiln.

To seal the kiln fully, the chimney pipe is pulled, a metal cap is placed on top, and more clay and earth is piled on top.  At the other end of the kiln, the fire-box entrance is stacked with fire bricks and also sealed with clay and earth.

Removing the ash soil before lifting the steel lids.
Removing the ash soil before lifting the steel lids

The kiln is then left for another day or two in its air-tight state to cool down slowly.  When things are cool enough that the fire is certainly out, and the chamber can be worked in, the ash soil and the steel panel are removed and the charcoal is revealed!

Finished charcoal!
Finished charcoal!

At this point, water needs to be kept on hand, because there can be hot spots in the charcoal which could potentially ignite when exposed to the air.

If all has gone well, there will be a large amount of charcoal remaining in the kiln, and there will be little to no partially burned wood.

The charcoal used at the Utano household is separated into two separate categories, that for the shichirin (cooking), and that for the kotatsu (keeping warm).  The charcoal reserved for the kotatsu is usually harder and denser.  This means it will burn longer and you don’t have to crawl under the table so often to stoke it to keep you warm.

Unloading the kiln
Unloading the kiln

When removing the charcoal, it’s important to wear a mask.  There is dust flying everywhere, and when you bend down into the kiln to pick up chunks of ashy coal, you don’t want to be inhaling that stuff.  This part of the job definitely gets you dirty.

Once all the larger charcoal chunks are removed and boxed, the small remaining pieces on the floor are sifted and the burnt bamboo slats removed.  The ashes are then shoveled out and the kiln is ready to go for another batch!

The firing itself takes 40-55 hours or so, with another 24-48 hours of cooling.  In about a week and a half’s time, I was able to help with unloading one batch, and two complete start-to-finish firings.  It is a really interesting process, and thanks to Utano san I was able to get fully involved in every step both times, so I think I got a good feel for things.  Perhaps we’ll be building one of these kilns on Ojika ourselves one day, but in the meantime we’ve got some to start our transition to a self-sustained life!

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