Water filter charcoal production – a true labour of love
Wood and plants such as bamboo, have a large number of vessels that carry water and nutrients up from the earth when they are alive. The types of charcoal that are suitable for water filtration are made using a slow and careful process, so that these fine vessels remain intact, leaving a highly porous and permeable structure. (You could say charcoal is the carbonised skeleton of wood and plants). The size of the pores varies – anything from 50 nm to less than 1nm. (1nm = 1 billionth metre). So when water roams through those myriad porous cavities, chemical constituents such as chlorine are trapped in the cavities, removing the familiar tap water taste and odour.
If we were able to unfold all the pores and spread them on a flat surface, amazingly 1g of high quality charcoal could cover between one and three tennis courts – depending on the type of wood and processing temperature. Generally bamboo charcoal made at 800-1000 degrees is considered to be the most porous – and it is this kind of charcoal that has a surface area equivalent to up to three tennis courts per gram.
In Japan, people who use charcoal for water filtering at home tend to use either ‘binchotan’ or bamboo charcoal. Binchotan is an oak wood charcoal, which is very tough and heavy. For many centuries it has been an indispensable feature of high-end restaurant grills, as it generates an excellent quality, long-lasting flame that adds a wonderful flavour to meat and fish. It happens to make a rather good water filter too. ‘Kishu binchotan’ made in the Kishu region of south west Japan, is considered the best of its kind.
Bamboo charcoal tends to be made mostly for non-fuel uses. Due to its fantastic ability to absorb pollutants both in air and water, it is widely used as a natural water filter and air purifier. Bamboo grows in most parts of Japan and so bamboo charcoal is made throughout the country.
Whether it’s binchotan or bamboo charcoal, well-made charcoal is the result of real craftsmanship. It is almost always made in traditional clay kilns. Charcoal making is all about heating wood or plants without oxygen (or almost) and experienced charcoal makers have their own kiln design and temperature control techniques. They raise the kiln temperature slowly over several days to ensure thorough and even carbonisation. The process culminates with the ‘nerashi’, in which air is blown into the kiln in order to raise the temperature to 1000 degree or more. In the case of binchotan, after the ‘nerashi’, the charcoal is pulled out of the kiln while it’s still red-hot and extinguished by being covered with ashes. By contrast, bamboo charcoal is usually extinguished inside the kiln by sealing the air passages and it is left for a few days to cool down. In either case, it takes 10-14 days, in a labour of love. Charcoal made in this way is very ‘pure’ with a very high carbon content of, typically, 95% – the remainder is mainly minerals.
Other characteristics of slowly made high temperature charcoal pieces are that they tend to have a silvery sheen and are much harder and heavier than ordinary barbeque charcoal – which can be a bit ‘woody’. They are also beautiful objects. It seems only right that two weeks of hard work create not only a highly versatile charcoal, but also one that is aesthetically attractive and appeals to the human senses.