Blowing up the merits of charcoal


When I was 12, chemistry didn’t interest me much until I found a battered old book in the school library that gave detailed instructions on the making of gunpowder. I still remember the recipe, which includes 75 percent potassium nitrate, otherwise known as saltpeter, and 10 percent charcoal.

The best charcoal for gunpowder is made from willow. Gunpowder burns very rapidly and if confined will explode. During this process 43 percent of the powder goes gaseous and the rest is mostly smoke.

After some very smoky experiments I finally managed to create some enormous fiery fizzes and a few deeply satisfying loud bangs. I had begun to collect antique flintlock guns, and managed to load and fire a couple of them with my homemade gunpowder. It was enormous fun, and I could have done some serious damage to the local crows, pigeons and rabbits, but the noise was so loud it usually drew the attention of curious adults. I had to give up these experiments for fear of losing my collection of flintlocks.

Otherwise my boyhood interest in chemistry was not much revived until the age of 15, when I learned that fascinating results could be obtained with sugars, water, yeast, a little time and then some fiddling that involved heat, a container for slow boiling, some copper tubing and a cooling system. Some horrendous and hard-to-explain headaches eventually put an end to these nefarious distillations (until I became an adviser for Nikka whisky and could do it legally).

Boys will be boys, after all.

This comes to mind because nowadays we are making charcoal here in Kurohime. No, not for gunpowder! Honestly! We found the ruins of an old stone charcoal kiln in our woods, and Mr. Matsuki, our woodsman, rebuilt it. The kiln had lain dormant for a few years, but as it is time to start trimming out some trees again, he rebuilt it and has been firing it for a couple of weeks now.

From your childhood chemistry lessons you may remember that, when a plant grows, carbon dioxide (CO2) is broken down and combines with oxygen (O2) and water (H2O) to make cellulose (C6H1005). If cellulose is burned with enough air, complete oxidation takes place, forming CO2 and water vapor. If the air is limited and the burning incomplete, charcoal is left. Charcoal is black and porous, and is widely used as fuel, as an adsorbent, as a filter and so on. It can also give some relief from indigestion. We feed charcoal to our pigs everyday after they’ve eaten for this reason. Whether or not it reduces the pigs’ farting I haven’t tried to measure, but it probably does.

The charcoal will produce a little revenue for the woodland trust, for we sell it to local pensions and private individuals for outdoor cooking. We make charcoal out of all kinds of wood, but much of it is made from hardwoods, such as oak and wild cherry. We choose spindly trees and branches that have almost stopped growing and whose presence impedes the growth of more vigorous and healthy neighbors.

After the kiln is stacked and fired, the entranceway is blocked, bar one small hole at the bottom and another one at the top of the stone wall at the back.

For a couple of days, what comes out of the chimney hole is mostly dense, pungent steam. Later you get a thinner smoke and hot, clear gases. We use a long metal chimney and a large can to collect the liquid distillate from the kiln. This is creosote, which is very popular among organic farmers as a natural and effective pesticide. The stuff we get contains water, creosol (an aromatic, oily C8H10O2) and other phenols. It can also be used to preserve wood and as sheep dip.

When Mr. Matsuki knows the time is right, (which he can tell from the look and smell of the smoke), he opens the stone and clay wall blocking the entrance. This is crucial, for as more air goes in, the charcoal gets almost white hot, and has to be raked out and smothered with a kind of earth before it burns itself to ashes. Peeping into the kiln, you can see the vividly glowing stacks of charcoal, the original shape of the wood remains, but reduced to about three-quarters the size and a quarter of the weight. Lovely blue flames, which I believe are caused by burning carbon monoxide, slowly undulate over the red and orange glow of the solids. This method produces a slightly grayish charcoal.

Another method is to totally seal off the little hole and the chimney hole in the final stages, depriving the kiln of all oxygen, then waiting a few days for the charcoal inside to cool off so that it cannot start burning again when exposed to air. This method makes a much blacker, denser, heavier charcoal, which is favored for tea ceremonies. We intend to try making some of this stuff later in the year when it is much colder.

It was largely the controlled and balanced trimming of the woods for charcoal and firewood, and fallen leaves for fertilizer, that kept the traditional woods of Japan so healthy. These local woods were called sato yama (“village mountain”) to differentiate them from the great forests beyond. Careful tending of woodlands not only produces fuel and fertilizer, but also all kinds of mushrooms, wild mountain vegetables and traditional medicines. These woods provided a habitat for wildlife and acted as “green dams” that would hold water to be slowly released in small springs and streams. Without such tending, Japanese woodlands would have soon become a choked, tangled, unproductive mess. I could give many other reasons why controlled trimming and charcoal production improve the habitat, but then the article would be too long and my editor would cut out the gunpowder bit, and I don’t want that.

Recently, it has become quite popular to keep a little charcoal in your room, because its properties of adsorption improve the air, especially if there are smokers in the house.

Our kiln is traditional, the entrance covered with a thatched roof. As it is close to the road a lot of people, especially locals, stop to watch and talk nostalgically of the old days, when charcoal kilns were a far more common sight.