The Kishu charcoals, also called "Kishu Binchotan" or "Wakayama Binchotan", are activated coals produced in Wakayama Prefecture, in the southern part of Japan. The term "activated" refers to a specific production process. To make charcoal, one needs to burn wood, of course, but obtaining activated coals is a much more complex operation. It is detailed here below.
The best binchotan are produced is in the Kii Peninsula, south of Kyoto. This mountainous area is covered by a dense forest, and is called "the land of trees". A varied arboriculture developed there, and the area is known throughout Japan for its citrus fruits (mikan) and plums (ume).
On these hills grows an oak tree called "Ubamegashi", a medium-sized tree, extremely hard and dense; it sinks when put into water. Ubamegashi has been exploited for thousands of years by a few foresters who manage the production of the most recognized coals throughout Asia.
Ubamegashi wood is cut into long and thin logs that are made straight by adding shims. The wood is stored for a few weeks to dry. After drying, the logs are inserted vertically into a clay oven lit by fire. Two phases will then succeed.
1. Carbonisation phase: Wood will burn slowly, at a low temperature (about 400°C) for several days. The wood slowly transforms into coals and millions of microscopic pores will apear on its surface. At this time, pores are filled with tar.
2. Activation phase: After few days of carbonisation, the door is suddenly opened, air rushes in it, and triggers intense combustion. The temperature increases significantly to up to 1200°C. Tars who were imprisoned in the pores volatilize as a result of the intense heat.
Tars contained in the pores created during the carbonization stage will volatilize under the effect of intense heat and will thus form a very large exchange surface corresponding to about 1000m² per gram of carbon! This is what gives to the Kishu coals their adsorption capacities, free pores from any substance.
Adsorption (not to be confused with absorption) is the phenomenon in which molecules present in suspension in a liquid (or a gas) bind to the solid surface with which they come into contact.
According to this principle, particles responsible for unpleasant tastes and odors of tap water stick to the surface of coal.
This principle is commonly used in the industry; certain devices using activated carbon to capture chlorine, pesticides and herbicides, benzene, radon, solvents and other chemicals. Activated coals are very often found in powder for clarifying liquids such as beer.