[Terrapreta] torrefaction vs. carbonization for fuel

[Gerald Van Koeverden]

This discussion of torrefaction vs. carbonization has generated a  
question in my mind...

Torrefied wood is apparently also called "grey charcoal".  If it  
takes only half of the energy to produce this grey charcoal, why  
don't we hear of villagers producing it?  Is it a technological  
problem (which we should be able to provide) or is there a special  
advantage for cooking in burning "black charcoal", other than the  
charcoal taste,  the higher temperatures that might be achieved by  
charcoal?

Why take the extra step from grey to black charcoal?  Certainly, we  
are not making any overall gain in energy by doing so.

Gerrit