So any biochar you make isn't just burning a fire and picking up the scraps.. it's hard wood to begin with and you cook the wood usually inside of a sealed can with holes at the bottom and you place that can of hard wood inside another can or barrel and place wood around it to burn.. I put a top on the second barrel as well but I duct the smoke up so the heat gets more intense inside the inner can/barrel... flames don't actually come in contact with any of the hard wood inside the inner barrel... basically your cooking wood in a barrel without it all burning into ash. Now you can get bichar from a camp fire or open flame but your losing most of it to combustion wear as when you heat it up sealed in a barrel with only holes at the bottom to vent smoke&gasses that is being heated by an outside flame source then all of the hardwood inside the sealed can (with vent holes at the bottom)will all become bichar without losing most of it to combustion like you would in a typical fire
