The goal of making biochar is to burn off all the chemicals of the plants so you are left with almost exclusively carbon (charcoal). The goal is different than making charcoal for a barbeque. I don't think they are focussed on removing the other chemicals-they just want to get it to where it will burn well for a long time. Biochar is best when it has nothing left to burn.
Then you typically crush it to increase surface area. I put mine between two panels of plywood and every time I drive, I go over it. I know. Pretty blue collar, huh? Then I put it in 5 gallon buckets and pour nutrition through it. Typically I use a mixture of regular
compost, worm "casting" compost, maybe some old rotten fruit, maybe old rotten wood or mycelium and urea. I took Redhawk's advice to not just soak it. It makes sense because you want to select for aerobic microbes. You are making hotels for them.
John S
PDX OR