Performance
The efficiency of coal also shows a certain deviation from the type of wood. There is some evidence that the content of lignin in the wood has a positive effect on the performance of coal, a high lignin content gives a high yield of charcoal. A dense wood also tends to give a coal dense and strong, which is also desirable. However, very dense wood sometimes produces coal friable since the wood tends to desmenuzarse during carbonization.

The friability coal increases with rising temperature carbonization and content of carbon fixed increases while the content of volatile substances decreases. A temperature of 450 to 500 ° C provides an optimal balance between the desire to friability and a high content of carbon fixed.

The many possible variables in carbonization yield optimal difficult to specify a procedure generally the best results can be obtained using hardwoods healthy, medium-density to high. The wood should be as dry as possible and usually cracked well, to remove pieces larger than 20 cm thick. Firewood that must be burned in furnaces or graves, and start to dry carbonization of the remnant, may be inferior and lower section. Its sole function is to produce heat to dry and warm the remaining at a temperature of carbonization.

Efforts should be made to reach a final temperature of around 500 ° C in the interior of the entire burden, which the graves becomes difficult, because air circulation and cooling effects are irregular and there are cold spots, obtaining blight or not charred wood. By trying to reach a final overall temperature of 500 ° C in a pit or oven, where air circulation is poor or erratic, it may be that some coal is burned into ashes, leaving other parts of the load only partially carbonized. Hence the importance of using well-designed ovens, made to function properly efficient production of charcoal.